xref: /template/mikio/inc/stemmechanics/lesserphp/lessc.inc.php (revision a92686aa569bf19e6b4530af2d5a1a53e4e0f66b)

<?php

/**
 * lessphp v0.7.1
 * http://leafo.net/lessphp
 *
 * LESS CSS compiler, adapted from http://lesscss.org
 *
 * Copyright 2013, Leaf Corcoran <leafot@gmail.com>
 * Copyright 2016, Marcus Schwarz <github@maswaba.de>
 * Copyright 2024, James Collins <james@stemmechanics.com.au>
 * Licensed under MIT or GPLv3, see LICENSE
 */


/**
 * The LESS compiler and parser.
 *
 * Converting LESS to CSS is a three stage process. The incoming file is parsed
 * by `lessc_parser` into a syntax tree, then it is compiled into another tree
 * representing the CSS structure by `lessc`. The CSS tree is fed into a
 * formatter, like `lessc_formatter` which then outputs CSS as a string.
 *
 * During the first compile, all values are *reduced*, which means that their
 * types are brought to the lowest form before being dump as strings. This
 * handles math equations, variable dereferences, and the like.
 *
 * The `parse` function of `lessc` is the entry point.
 *
 * In summary:
 *
 * The `lessc` class creates an instance of the parser, feeds it LESS code,
 * then transforms the resulting tree to a CSS tree. This class also holds the
 * evaluation context, such as all available mixins and variables at any given
 * time.
 *
 * The `lessc_parser` class is only concerned with parsing its input.
 *
 * The `lessc_formatter` takes a CSS tree, and dumps it to a formatted string,
 * handling things like indentation.
 */
class lessc {
    static public $VERSION = "v0.7.1";

    static public $TRUE = array("keyword", "true");
    static public $FALSE = array("keyword", "false");

    protected $libFunctions = array();
    protected $registeredVars = array();
    protected $preserveComments = false;

    public $vPrefix = '@'; // prefix of abstract properties
    public $mPrefix = '$'; // prefix of abstract blocks
    public $parentSelector = '&';

    static public $lengths = array( "px", "m", "cm", "mm", "in", "pt", "pc" );
    static public $times = array( "s", "ms" );
    static public $angles = array( "rad", "deg", "grad", "turn" );

    static public $lengths_to_base = array( 1, 3779.52755906, 37.79527559, 3.77952756, 96, 1.33333333, 16  );
    public $importDisabled = false;
    public $importDir = array();

    protected $numberPrecision = null;

    protected $allParsedFiles = array();

    // set to the parser that generated the current line when compiling
    // so we know how to create error messages
    protected $sourceParser = null;
    protected $sourceLoc = null;

    static protected $nextImportId = 0; // uniquely identify imports

    protected $parser;
    protected $env;
    protected $scope;
    protected $formatter;

    // attempts to find the path of an import url, returns null for css files
    protected function findImport($url) {
        foreach ((array)$this->importDir as $dir) {
            $full = $dir.(substr($dir, -1) != '/' ? '/' : '').$url;
            if ($this->fileExists($file = $full.'.less') || $this->fileExists($file = $full)) {
                return $file;
            }
        }

        return null;
    }

    protected function fileExists($name) {
        return is_file($name);
    }

    static public function compressList($items, $delim) {
        if (!isset($items[1]) && isset($items[0])) return $items[0];
        else return array('list', $delim, $items);
    }

    static public function preg_quote($what) {
        return preg_quote($what, '/');
    }

    protected function tryImport($importPath, $parentBlock, $out) {
        if ($importPath[0] == "function" && $importPath[1] == "url") {
            $importPath = $this->flattenList($importPath[2]);
        }

        $str = $this->coerceString($importPath);
        if ($str === null) return false;

        $url = $this->compileValue($this->lib_e($str));

        // don't import if it ends in css
        if (substr_compare($url, '.css', -4, 4) === 0) return false;

        $realPath = $this->findImport($url);

        if ($realPath === null) return false;

        if ($this->importDisabled) {
            return array(false, "/* import disabled */");
        }

        if (isset($this->allParsedFiles[realpath($realPath)])) {
            return array(false, null);
        }

        $this->addParsedFile($realPath);
        $parser = $this->makeParser($realPath);
        $root = $parser->parse(file_get_contents($realPath));

        // set the parents of all the block props
        foreach ($root->props as $prop) {
            if ($prop[0] == "block") {
                $prop[1]->parent = $parentBlock;
            }
        }

        // copy mixins into scope, set their parents
        // bring blocks from import into current block
        // TODO: need to mark the source parser	these came from this file
        foreach ($root->children as $childName => $child) {
            if (isset($parentBlock->children[$childName])) {
                $parentBlock->children[$childName] = array_merge(
                    $parentBlock->children[$childName],
                    $child);
            } else {
                $parentBlock->children[$childName] = $child;
            }
        }

        $pi = pathinfo($realPath);
        $dir = $pi["dirname"];

        [$top, $bottom] = $this->sortProps($root->props, true);
        $this->compileImportedProps($top, $parentBlock, $out, $parser, $dir);

        return array(true, $bottom, $parser, $dir);
    }

    protected function compileImportedProps($props, $block, $out, $sourceParser, $importDir) {
        $oldSourceParser = $this->sourceParser;

        $oldImport = $this->importDir;

        // TODO: this is because the importDir api is stupid
        $this->importDir = (array)$this->importDir;
        array_unshift($this->importDir, $importDir);

        foreach ($props as $prop) {
            $this->compileProp($prop, $block, $out);
        }

        $this->importDir = $oldImport;
        $this->sourceParser = $oldSourceParser;
    }

    /**
     * Recursively compiles a block.
     *
     * A block is analogous to a CSS block in most cases. A single LESS document
     * is encapsulated in a block when parsed, but it does not have parent tags
     * so all of it's children appear on the root level when compiled.
     *
     * Blocks are made up of props and children.
     *
     * Props are property instructions, array tuples which describe an action
     * to be taken, eg. write a property, set a variable, mixin a block.
     *
     * The children of a block are just all the blocks that are defined within.
     * This is used to look up mixins when performing a mixin.
     *
     * Compiling the block involves pushing a fresh environment on the stack,
     * and iterating through the props, compiling each one.
     *
     * See lessc::compileProp()
     *
     */
    protected function compileBlock($block) {
        switch ($block->type) {
            case "root":
                $this->compileRoot($block);
                break;
            case null:
                $this->compileCSSBlock($block);
                break;
            case "media":
                $this->compileMedia($block);
                break;
            case "directive":
                $name = "@" . $block->name;
                if (!empty($block->value)) {
                    $name .= " " . $this->compileValue($this->reduce($block->value));
                }

                $this->compileNestedBlock($block, array($name));
                break;
            default:
                $block->parser->throwError("unknown block type: $block->type\n", $block->count);
        }
    }

    protected function compileCSSBlock($block) {
        $env = $this->pushEnv();

        $selectors = $this->compileSelectors($block->tags);
        $env->selectors = $this->multiplySelectors($selectors);
        $out = $this->makeOutputBlock(null, $env->selectors);

        $this->scope->children[] = $out;
        $this->compileProps($block, $out);

        $block->scope = $env; // mixins carry scope with them!
        $this->popEnv();
    }

    protected function compileMedia($media) {
        $env = $this->pushEnv($media);
        $parentScope = $this->mediaParent($this->scope);

        $query = $this->compileMediaQuery($this->multiplyMedia($env));

        $this->scope = $this->makeOutputBlock($media->type, array($query));
        $parentScope->children[] = $this->scope;

        $this->compileProps($media, $this->scope);

        if (count($this->scope->lines) > 0) {
            $orphanSelelectors = $this->findClosestSelectors();
            if (!is_null($orphanSelelectors)) {
                $orphan = $this->makeOutputBlock(null, $orphanSelelectors);
                $orphan->lines = $this->scope->lines;
                array_unshift($this->scope->children, $orphan);
                $this->scope->lines = array();
            }
        }

        $this->scope = $this->scope->parent;
        $this->popEnv();
    }

    protected function mediaParent($scope) {
        while (!empty($scope->parent)) {
            if (!empty($scope->type) && $scope->type != "media") {
                break;
            }
            $scope = $scope->parent;
        }

        return $scope;
    }

    protected function compileNestedBlock($block, $selectors) {
        $this->pushEnv($block);
        $this->scope = $this->makeOutputBlock($block->type, $selectors);
        $this->scope->parent->children[] = $this->scope;

        $this->compileProps($block, $this->scope);

        $this->scope = $this->scope->parent;
        $this->popEnv();
    }

    protected function compileRoot($root) {
        $this->pushEnv();
        $this->scope = $this->makeOutputBlock($root->type);
        $this->compileProps($root, $this->scope);
        $this->popEnv();
    }

    protected function compileProps($block, $out) {
        foreach ($this->sortProps($block->props) as $prop) {
            $this->compileProp($prop, $block, $out);
        }
        $out->lines = $this->deduplicate($out->lines);
    }

    /**
     * Deduplicate lines in a block. Comments are not deduplicated. If a
     * duplicate rule is detected, the comments immediately preceding each
     * occurence are consolidated.
     */
    protected function deduplicate($lines) {
        $unique = array();
        $comments = array();

        foreach($lines as $line) {
            if (strpos($line, '/*') === 0) {
                $comments[] = $line;
                continue;
            }
            if (!in_array($line, $unique)) {
                $unique[] = $line;
            }
            array_splice($unique, array_search($line, $unique), 0, $comments);
            $comments = array();
        }
        return array_merge($unique, $comments);
    }

    protected function sortProps($props, $split = false) {
        $vars = array();
        $imports = array();
        $other = array();
        $stack = array();

        foreach ($props as $prop) {
            switch ($prop[0]) {
                case "comment":
                    $stack[] = $prop;
                    break;
                case "assign":
                    $stack[] = $prop;
                    if (isset($prop[1][0]) && $prop[1][0] == $this->vPrefix) {
                        $vars = array_merge($vars, $stack);
                    } else {
                        $other = array_merge($other, $stack);
                    }
                    $stack = array();
                    break;
                case "import":
                    $id = self::$nextImportId++;
                    $prop[] = $id;
                    $stack[] = $prop;
                    $imports = array_merge($imports, $stack);
                    $other[] = array("import_mixin", $id);
                    $stack = array();
                    break;
                default:
                    $stack[] = $prop;
                    $other = array_merge($other, $stack);
                    $stack = array();
                    break;
            }
        }
        $other = array_merge($other, $stack);

        if ($split) {
            return array(array_merge($vars, $imports, $vars), $other);
        } else {
            return array_merge($vars, $imports, $vars, $other);
        }
    }

    protected function compileMediaQuery($queries) {
        $compiledQueries = array();
        foreach ($queries as $query) {
            $parts = array();
            foreach ($query as $q) {
                switch ($q[0]) {
                    case "mediaType":
                        $parts[] = implode(" ", array_slice($q, 1));
                        break;
                    case "mediaExp":
                        if (isset($q[2])) {
                            $parts[] = "($q[1]: " .
                                $this->compileValue($this->reduce($q[2])) . ")";
                        } else {
                            $parts[] = "($q[1])";
                        }
                        break;
                    case "variable":
                        $parts[] = $this->compileValue($this->reduce($q));
                        break;
                }
            }

            if (count($parts) > 0) {
                $compiledQueries[] =  implode(" and ", $parts);
            }
        }

        $out = "@media";
        if (!empty($parts)) {
            $out .= " " .
                implode($this->formatter->selectorSeparator, $compiledQueries);
        }
        return $out;
    }

    protected function multiplyMedia($env, $childQueries = null) {
        if (is_null($env) ||
            !empty($env->block->type) && $env->block->type != "media")
        {
            return $childQueries;
        }

        // plain old block, skip
        if (empty($env->block->type)) {
            return $this->multiplyMedia($env->parent, $childQueries);
        }

        $out = array();
        $queries = $env->block->queries;
        if (is_null($childQueries)) {
            $out = $queries;
        } else {
            foreach ($queries as $parent) {
                foreach ($childQueries as $child) {
                    $out[] = array_merge($parent, $child);
                }
            }
        }

        return $this->multiplyMedia($env->parent, $out);
    }

    protected function expandParentSelectors(&$tag, $replace) {
        $parts = explode("$&$", $tag);
        $count = 0;
        foreach ($parts as &$part) {
            $part = str_replace($this->parentSelector, $replace, $part, $c);
            $count += $c;
        }
        $tag = implode($this->parentSelector, $parts);
        return $count;
    }

    protected function findClosestSelectors() {
        $env = $this->env;
        $selectors = null;
        while ($env !== null) {
            if (isset($env->selectors)) {
                $selectors = $env->selectors;
                break;
            }
            $env = $env->parent;
        }

        return $selectors;
    }


    // multiply $selectors against the nearest selectors in env
    protected function multiplySelectors($selectors) {
        // find parent selectors

        $parentSelectors = $this->findClosestSelectors();
        if (is_null($parentSelectors)) {
            // kill parent reference in top level selector
            foreach ($selectors as &$s) {
                $this->expandParentSelectors($s, "");
            }

            return $selectors;
        }

        $out = array();
        foreach ($parentSelectors as $parent) {
            foreach ($selectors as $child) {
                $count = $this->expandParentSelectors($child, $parent);

                // don't prepend the parent tag if & was used
                if ($count > 0) {
                    $out[] = trim($child);
                } else {
                    $out[] = trim($parent . ' ' . $child);
                }
            }
        }

        return $out;
    }

    // reduces selector expressions
    protected function compileSelectors($selectors) {
        $out = array();

        foreach ($selectors as $s) {
            if (is_array($s)) {
                [, $value] = $s;
                $out[] = trim($this->compileValue($this->reduce($value)));
            } else {
                $out[] = $s;
            }
        }

        return $out;
    }

    protected function eq($left, $right) {
        return $left == $right;
    }

    protected function patternMatch($block, $orderedArgs, $keywordArgs) {
        // match the guards if it has them
        // any one of the groups must have all its guards pass for a match
        if (!empty($block->guards)) {
            $groupPassed = false;
            foreach ($block->guards as $guardGroup) {
                foreach ($guardGroup as $guard) {
                    $this->pushEnv();
                    $this->zipSetArgs($block->args, $orderedArgs, $keywordArgs);

                    $negate = false;
                    if ($guard[0] == "negate") {
                        $guard = $guard[1];
                        $negate = true;
                    }

                    $passed = $this->reduce($guard) == self::$TRUE;
                    if ($negate) $passed = !$passed;

                    $this->popEnv();

                    if ($passed) {
                        $groupPassed = true;
                    } else {
                        $groupPassed = false;
                        break;
                    }
                }

                if ($groupPassed) break;
            }

            if (!$groupPassed) {
                return false;
            }
        }

        if (empty($block->args)) {
            return $block->isVararg || empty($orderedArgs) && empty($keywordArgs);
        }

        $remainingArgs = $block->args;
        if ($keywordArgs) {
            $remainingArgs = array();
            foreach ($block->args as $arg) {
                if ($arg[0] == "arg" && isset($keywordArgs[$arg[1]])) {
                    continue;
                }

                $remainingArgs[] = $arg;
            }
        }

        $i = -1; // no args
        // try to match by arity or by argument literal
        foreach ($remainingArgs as $i => $arg) {
            switch ($arg[0]) {
                case "lit":
                    if (empty($orderedArgs[$i]) || !$this->eq($arg[1], $orderedArgs[$i])) {
                        return false;
                    }
                    break;
                case "arg":
                    // no arg and no default value
                    if (!isset($orderedArgs[$i]) && !isset($arg[2])) {
                        return false;
                    }
                    break;
                case "rest":
                    $i--; // rest can be empty
                    break 2;
            }
        }

        if ($block->isVararg) {
            return true; // not having enough is handled above
        } else {
            $numMatched = $i + 1;
            // greater than because default values always match
            return $numMatched >= count($orderedArgs);
        }
    }

    protected function patternMatchAll($blocks, $orderedArgs, $keywordArgs, $skip=array()) {
        $matches = null;
        foreach ($blocks as $block) {
            // skip seen blocks that don't have arguments
            if (isset($skip[$block->id]) && !isset($block->args)) {
                continue;
            }

            if ($this->patternMatch($block, $orderedArgs, $keywordArgs)) {
                $matches[] = $block;
            }
        }

        return $matches;
    }

    // attempt to find blocks matched by path and args
    protected function findBlocks($searchIn, $path, $orderedArgs, $keywordArgs, $seen=array()) {
        if ($searchIn == null) return null;
        if (isset($seen[$searchIn->id])) return null;
        $seen[$searchIn->id] = true;

        $name = $path[0];

        if (isset($searchIn->children[$name])) {
            $blocks = $searchIn->children[$name];
            if (count($path) == 1) {
                $matches = $this->patternMatchAll($blocks, $orderedArgs, $keywordArgs, $seen);
                if (!empty($matches)) {
                    // This will return all blocks that match in the closest
                    // scope that has any matching block, like lessjs
                    return $matches;
                }
            } else {
                $matches = array();
                foreach ($blocks as $subBlock) {
                    $subMatches = $this->findBlocks($subBlock,
                        array_slice($path, 1), $orderedArgs, $keywordArgs, $seen);

                    if (!is_null($subMatches)) {
                        foreach ($subMatches as $sm) {
                            $matches[] = $sm;
                        }
                    }
                }

                return count($matches) > 0 ? $matches : null;
            }
        }
        if ($searchIn->parent === $searchIn) return null;
        return $this->findBlocks($searchIn->parent, $path, $orderedArgs, $keywordArgs, $seen);
    }

    // sets all argument names in $args to either the default value
    // or the one passed in through $values
    protected function zipSetArgs($args, $orderedValues, $keywordValues) {
        $assignedValues = array();

        $i = 0;
        foreach ($args as  $a) {
            if ($a[0] == "arg") {
                if (isset($keywordValues[$a[1]])) {
                    // has keyword arg
                    $value = $keywordValues[$a[1]];
                } elseif (isset($orderedValues[$i])) {
                    // has ordered arg
                    $value = $orderedValues[$i];
                    $i++;
                } elseif (isset($a[2])) {
                    // has default value
                    $value = $a[2];
                } else {
                    $this->throwError("Failed to assign arg " . $a[1]);
                    $value = null; // :(
                }

                $value = $this->reduce($value);
                $this->set($a[1], $value);
                $assignedValues[] = $value;
            } else {
                // a lit
                $i++;
            }
        }

        // check for a rest
        $last = end($args);
        if ($last !== false && $last[0] === "rest") {
            $rest = array_slice($orderedValues, count($args) - 1);
            $this->set($last[1], $this->reduce(array("list", " ", $rest)));
        }

        // wow is this the only true use of PHP's + operator for arrays?
        $this->env->arguments = $assignedValues + $orderedValues;
    }

    // compile a prop and update $lines or $blocks appropriately
    protected function compileProp($prop, $block, $out) {
        // set error position context
        $this->sourceLoc = isset($prop[-1]) ? $prop[-1] : -1;

        switch ($prop[0]) {
            case 'assign':
                [, $name, $value] = $prop;
                if ($name[0] == $this->vPrefix) {
                    $this->set($name, $value);
                } else {
                    $out->lines[] = $this->formatter->property($name,
                        $this->compileValue($this->reduce($value)));
                }
                break;
            case 'block':
                [, $child] = $prop;
                $this->compileBlock($child);
                break;
            case 'ruleset':
            case 'mixin':
                [, $path, $args, $suffix] = $prop;

                $orderedArgs = array();
                $keywordArgs = array();
                foreach ((array)$args as $arg) {
                    $argval = null;
                    switch ($arg[0]) {
                        case "arg":
                            if (!isset($arg[2])) {
                                $orderedArgs[] = $this->reduce(array("variable", $arg[1]));
                            } else {
                                $keywordArgs[$arg[1]] = $this->reduce($arg[2]);
                            }
                            break;

                        case "lit":
                            $orderedArgs[] = $this->reduce($arg[1]);
                            break;
                        default:
                            $this->throwError("Unknown arg type: " . $arg[0]);
                    }
                }

                $mixins = $this->findBlocks($block, $path, $orderedArgs, $keywordArgs);

                if ($mixins === null) {
                    $block->parser->throwError("{$prop[1][0]} is undefined", $block->count);
                }

                if(strpos($prop[1][0], "$") === 0) {
                    //Use Ruleset Logic - Only last element
                    $mixins = array(array_pop($mixins));
                }

                foreach ($mixins as $mixin) {
                    if ($mixin === $block && !$orderedArgs) {
                        continue;
                    }

                    $haveScope = false;
                    if (isset($mixin->parent->scope)) {
                        $haveScope = true;
                        $mixinParentEnv = $this->pushEnv();
                        $mixinParentEnv->storeParent = $mixin->parent->scope;
                    }

                    $haveArgs = false;
                    if (isset($mixin->args)) {
                        $haveArgs = true;
                        $this->pushEnv();
                        $this->zipSetArgs($mixin->args, $orderedArgs, $keywordArgs);
                    }

                    $oldParent = $mixin->parent;
                    if ($mixin != $block) $mixin->parent = $block;

                    foreach ($this->sortProps($mixin->props) as $subProp) {
                        if ($suffix !== null &&
                            $subProp[0] == "assign" &&
                            is_string($subProp[1]) &&
                            $subProp[1][0] != $this->vPrefix)
                        {
                            $subProp[2] = array(
                                'list', ' ',
                                array($subProp[2], array('keyword', $suffix))
                            );
                        }

                        $this->compileProp($subProp, $mixin, $out);
                    }

                    $mixin->parent = $oldParent;

                    if ($haveArgs) $this->popEnv();
                    if ($haveScope) $this->popEnv();
                }

                break;
            case 'raw':
                $out->lines[] = $prop[1];
                break;
            case "directive":
                [, $name, $value] = $prop;
                $out->lines[] = "@$name " . $this->compileValue($this->reduce($value)).';';
                break;
            case "comment":
                $out->lines[] = $prop[1];
                break;
            case "import";
                [, $importPath, $importId] = $prop;
                $importPath = $this->reduce($importPath);

                if (!isset($this->env->imports)) {
                    $this->env->imports = array();
                }

                $result = $this->tryImport($importPath, $block, $out);

                $this->env->imports[$importId] = $result === false ?
                    array(false, "@import " . $this->compileValue($importPath).";") :
                    $result;

                break;
            case "import_mixin":
                [,$importId] = $prop;
                $import = $this->env->imports[$importId];
                if ($import[0] === false) {
                    if (isset($import[1])) {
                        $out->lines[] = $import[1];
                    }
                } else {
                    [, $bottom, $parser, $importDir] = $import;
                    $this->compileImportedProps($bottom, $block, $out, $parser, $importDir);
                }

                break;
            default:
                $block->parser->throwError("unknown op: {$prop[0]}\n", $block->count);
        }
    }


    /**
     * Compiles a primitive value into a CSS property value.
     *
     * Values in lessphp are typed by being wrapped in arrays, their format is
     * typically:
     *
     *     array(type, contents [, additional_contents]*)
     *
     * The input is expected to be reduced. This function will not work on
     * things like expressions and variables.
     */
    public function compileValue($value) {
        switch ($value[0]) {
            case 'list':
                // [1] - delimiter
                // [2] - array of values
                return implode($value[1], array_map(array($this, 'compileValue'), $value[2]));
            case 'raw_color':
                if (!empty($this->formatter->compressColors)) {
                    return $this->compileValue($this->coerceColor($value));
                }
                return $value[1];
            case 'keyword':
                // [1] - the keyword
                return $value[1];
            case 'number':
                [, $num, $unit] = $value;
                // [1] - the number
                // [2] - the unit
                if ($this->numberPrecision !== null) {
                    $num = round($num, $this->numberPrecision);
                }
                return $num . $unit;
            case 'string':
                // [1] - contents of string (includes quotes)
                [, $delim, $content] = $value;
                foreach ($content as &$part) {
                    if (is_array($part)) {
                        $part = $this->compileValue($part);
                    }
                }
                return $delim . implode($content) . $delim;
            case 'color':
                // [1] - red component (either number or a %)
                // [2] - green component
                // [3] - blue component
                // [4] - optional alpha component
                [, $r, $g, $b] = $value;
                $r = round($r);
                $g = round($g);
                $b = round($b);

                if (count($value) == 5 && $value[4] != 1) { // rgba
                    return 'rgba('.$r.','.$g.','.$b.','.$value[4].')';
                }

                $h = sprintf("#%02x%02x%02x", $r, $g, $b);

                if (!empty($this->formatter->compressColors)) {
                    // Converting hex color to short notation (e.g. #003399 to #039)
                    if ($h[1] === $h[2] && $h[3] === $h[4] && $h[5] === $h[6]) {
                        $h = '#' . $h[1] . $h[3] . $h[5];
                    }
                }

                return $h;

            case 'function':
                [, $name, $args] = $value;
                return $name.'('.$this->compileValue($args).')';
            default: // assumed to be unit
                $this->throwError("unknown value type: $value[0]");
        }
    }

    protected function lib_pow($args) {
        [$base, $exp] = $this->assertArgs($args, 2, "pow");
        return array( "number", pow($this->assertNumber($base), $this->assertNumber($exp)), $args[2][0][2] );
    }

    protected function lib_pi() {
        return pi();
    }

    protected function lib_mod($args) {
        [$a, $b] = $this->assertArgs($args, 2, "mod");
        return array( "number", $this->assertNumber($a) % $this->assertNumber($b), $args[2][0][2] );
    }

    protected function lib_convert($args) {
        [$value, $to] = $this->assertArgs($args, 2, "convert");

        // If it's a keyword, grab the string version instead
        if( is_array( $to ) && $to[0] == "keyword" )
            $to = $to[1];

        return $this->convert( $value, $to );
    }

    protected function lib_abs($num) {
        return array( "number", abs($this->assertNumber($num)), $num[2] );
    }

    protected function lib_min($args) {
        $values = $this->assertMinArgs($args, 1, "min");

        $first_format = $values[0][2];

        $min_index = 0;
        $min_value = $values[0][1];

        for( $a = 0; $a < sizeof( $values ); $a++ )
        {
            $converted = $this->convert( $values[$a], $first_format );

            if( $converted[1] < $min_value )
            {
                $min_index = $a;
                $min_value = $values[$a][1];
            }
        }

        return $values[ $min_index ];
    }

    protected function lib_max($args) {
        $values = $this->assertMinArgs($args, 1, "max");

        $first_format = $values[0][2];

        $max_index = 0;
        $max_value = $values[0][1];

        for( $a = 0; $a < sizeof( $values ); $a++ )
        {
            $converted = $this->convert( $values[$a], $first_format );

            if( $converted[1] > $max_value )
            {
                $max_index = $a;
                $max_value = $values[$a][1];
            }
        }

        return $values[ $max_index ];
    }

    protected function lib_tan($num) {
        return tan($this->assertNumber($num));
    }

    protected function lib_sin($num) {
        return sin($this->assertNumber($num));
    }

    protected function lib_cos($num) {
        return cos($this->assertNumber($num));
    }

    protected function lib_atan($num) {
        $num = atan($this->assertNumber($num));
        return array("number", $num, "rad");
    }

    protected function lib_asin($num) {
        $num = asin($this->assertNumber($num));
        return array("number", $num, "rad");
    }

    protected function lib_acos($num) {
        $num = acos($this->assertNumber($num));
        return array("number", $num, "rad");
    }

    protected function lib_sqrt($num) {
        return sqrt($this->assertNumber($num));
    }

    protected function lib_extract($value) {
        [$list, $idx] = $this->assertArgs($value, 2, "extract");
        $idx = $this->assertNumber($idx);
        // 1 indexed
        if ($list[0] == "list" && isset($list[2][$idx - 1])) {
            return $list[2][$idx - 1];
        }
    }

    protected function lib_isnumber($value) {
        return $this->toBool($value[0] == "number");
    }

    protected function lib_isstring($value) {
        return $this->toBool($value[0] == "string");
    }

    protected function lib_iscolor($value) {
        return $this->toBool($this->coerceColor($value));
    }

    protected function lib_iskeyword($value) {
        return $this->toBool($value[0] == "keyword");
    }

    protected function lib_ispixel($value) {
        return $this->toBool($value[0] == "number" && $value[2] == "px");
    }

    protected function lib_ispercentage($value) {
        return $this->toBool($value[0] == "number" && $value[2] == "%");
    }

    protected function lib_isem($value) {
        return $this->toBool($value[0] == "number" && $value[2] == "em");
    }

    protected function lib_isrem($value) {
        return $this->toBool($value[0] == "number" && $value[2] == "rem");
    }

    protected function lib_rgbahex($color) {
        $color = $this->coerceColor($color);
        if (is_null($color))
            $this->throwError("color expected for rgbahex");

        return sprintf("#%02x%02x%02x%02x",
            isset($color[4]) ? $color[4]*255 : 255,
            $color[1],$color[2], $color[3]);
    }

    protected function lib_argb($color){
        return $this->lib_rgbahex($color);
    }

    /**
     * Given an url, decide whether to output a regular link or the base64-encoded contents of the file
     *
     * @param  array  $value either an argument list (two strings) or a single string
     * @return string        formatted url(), either as a link or base64-encoded
     */
    protected function lib_data_uri($value) {
        $mime = ($value[0] === 'list') ? $value[2][0][2] : null;
        $url = ($value[0] === 'list') ? $value[2][1][2][0] : $value[2][0];

        $fullpath = $this->findImport($url);

        if($fullpath && ($fsize = filesize($fullpath)) !== false) {
            // IE8 can't handle data uris larger than 32KB
            if($fsize/1024 < 32) {
                if(is_null($mime)) {
                    if(class_exists('finfo')) { // php 5.3+
                        $finfo = new finfo(FILEINFO_MIME);
                        $mime = explode('; ', $finfo->file($fullpath));
                        $mime = $mime[0];
                    } elseif(function_exists('mime_content_type')) { // PHP 5.2
                        $mime = mime_content_type($fullpath);
                    }
                }

                if(!is_null($mime)) // fallback if the mime type is still unknown
                    $url = sprintf('data:%s;base64,%s', $mime, base64_encode(file_get_contents($fullpath)));
            }
        }

        return 'url("'.$url.'")';
    }

    // utility func to unquote a string
    protected function lib_e($arg) {
        switch ($arg[0]) {
            case "list":
                $items = $arg[2];
                if (isset($items[0])) {
                    return $this->lib_e($items[0]);
                }
                $this->throwError("unrecognised input");
            case "string":
                $arg[1] = "";
                return $arg;
            case "keyword":
                return $arg;
            default:
                return array("keyword", $this->compileValue($arg));
        }
    }

    protected function lib__sprintf($args) {
        if ($args[0] != "list") return $args;
        $values = $args[2];
        $string = array_shift($values);
        $template = $this->compileValue($this->lib_e($string));

        $i = 0;
        if (preg_match_all('/%[dsa]/', $template, $m)) {
            foreach ($m[0] as $match) {
                $val = isset($values[$i]) ?
                    $this->reduce($values[$i]) : array('keyword', '');

                // lessjs compat, renders fully expanded color, not raw color
                if ($color = $this->coerceColor($val)) {
                    $val = $color;
                }

                $i++;
                $rep = $this->compileValue($this->lib_e($val));
                $template = preg_replace('/'.self::preg_quote($match).'/',
                    $rep, $template, 1);
            }
        }

        $d = $string[0] == "string" ? $string[1] : '"';
        return array("string", $d, array($template));
    }

    protected function lib_floor($arg) {
        $value = $this->assertNumber($arg);
        return array("number", floor($value), $arg[2]);
    }

    protected function lib_ceil($arg) {
        $value = $this->assertNumber($arg);
        return array("number", ceil($value), $arg[2]);
    }

    protected function lib_round($arg) {
        if($arg[0] != "list") {
            $value = $this->assertNumber($arg);
            return array("number", round($value), $arg[2]);
        } else {
            $value = $this->assertNumber($arg[2][0]);
            $precision = $this->assertNumber($arg[2][1]);
            return array("number", round($value, $precision), $arg[2][0][2]);
        }
    }

    protected function lib_unit($arg) {
        if ($arg[0] == "list") {
            [$number, $newUnit] = $arg[2];
            return array("number", $this->assertNumber($number),
                $this->compileValue($this->lib_e($newUnit)));
        } else {
            return array("number", $this->assertNumber($arg), "");
        }
    }

    /**
     * Helper function to get arguments for color manipulation functions.
     * takes a list that contains a color like thing and a percentage
     */
    public function colorArgs($args) {
        if ($args[0] != 'list' || count($args[2]) < 2) {
            return array(array('color', 0, 0, 0), 0);
        }
        [$color, $delta] = $args[2];
        $color = $this->assertColor($color);
        $delta = floatval($delta[1]);

        return array($color, $delta);
    }

    protected function lib_darken($args) {
        [$color, $delta] = $this->colorArgs($args);

        $hsl = $this->toHSL($color);
        $hsl[3] = $this->clamp($hsl[3] - $delta, 100);
        return $this->toRGB($hsl);
    }

    protected function lib_lighten($args) {
        [$color, $delta] = $this->colorArgs($args);

        $hsl = $this->toHSL($color);
        $hsl[3] = $this->clamp($hsl[3] + $delta, 100);
        return $this->toRGB($hsl);
    }

    protected function lib_saturate($args) {
        [$color, $delta] = $this->colorArgs($args);

        $hsl = $this->toHSL($color);
        $hsl[2] = $this->clamp($hsl[2] + $delta, 100);
        return $this->toRGB($hsl);
    }

    protected function lib_desaturate($args) {
        [$color, $delta] = $this->colorArgs($args);

        $hsl = $this->toHSL($color);
        $hsl[2] = $this->clamp($hsl[2] - $delta, 100);
        return $this->toRGB($hsl);
    }

    protected function lib_spin($args) {
        [$color, $delta] = $this->colorArgs($args);

        $hsl = $this->toHSL($color);

        $hsl[1] = $hsl[1] + $delta % 360;
        if ($hsl[1] < 0) $hsl[1] += 360;

        return $this->toRGB($hsl);
    }

    protected function lib_fadeout($args) {
        [$color, $delta] = $this->colorArgs($args);
        $color[4] = $this->clamp((isset($color[4]) ? $color[4] : 1) - $delta/100);
        return $color;
    }

    protected function lib_fadein($args) {
        [$color, $delta] = $this->colorArgs($args);
        $color[4] = $this->clamp((isset($color[4]) ? $color[4] : 1) + $delta/100);
        return $color;
    }

    protected function lib_hue($color) {
        $hsl = $this->toHSL($this->assertColor($color));
        return round($hsl[1]);
    }

    protected function lib_saturation($color) {
        $hsl = $this->toHSL($this->assertColor($color));
        return round($hsl[2]);
    }

    protected function lib_lightness($color) {
        $hsl = $this->toHSL($this->assertColor($color));
        return round($hsl[3]);
    }

    // get the alpha of a color
    // defaults to 1 for non-colors or colors without an alpha
    protected function lib_alpha($value) {
        if (!is_null($color = $this->coerceColor($value))) {
            return isset($color[4]) ? $color[4] : 1;
        }
    }

    // set the alpha of the color
    protected function lib_fade($args) {
        [$color, $alpha] = $this->colorArgs($args);
        $color[4] = $this->clamp($alpha / 100.0);
        return $color;
    }

    protected function lib_percentage($arg) {
        $num = $this->assertNumber($arg);
        return array("number", $num*100, "%");
    }

    // mixes two colors by weight
    // mix(@color1, @color2, [@weight: 50%]);
    // http://sass-lang.com/docs/yardoc/Sass/Script/Functions.html#mix-instance_method
    protected function lib_mix($args) {
        if ($args[0] != "list" || count($args[2]) < 2)
            $this->throwError("mix expects (color1, color2, weight)");

        [$first, $second] = $args[2];
        $first = $this->assertColor($first);
        $second = $this->assertColor($second);

        $first_a = $this->lib_alpha($first);
        $second_a = $this->lib_alpha($second);

        if (isset($args[2][2])) {
            $weight = $args[2][2][1] / 100.0;
        } else {
            $weight = 0.5;
        }

        $w = $weight * 2 - 1;
        $a = $first_a - $second_a;

        $w1 = (($w * $a == -1 ? $w : ($w + $a)/(1 + $w * $a)) + 1) / 2.0;
        $w2 = 1.0 - $w1;

        $new = array('color',
            $w1 * $first[1] + $w2 * $second[1],
            $w1 * $first[2] + $w2 * $second[2],
            $w1 * $first[3] + $w2 * $second[3],
        );

        if ($first_a != 1.0 || $second_a != 1.0) {
            $new[] = $first_a * $weight + $second_a * ($weight - 1);
        }

        return $this->fixColor($new);
    }

    protected function lib_contrast($args) {
        $darkColor  = array('color', 0, 0, 0);
        $lightColor = array('color', 255, 255, 255);
        $threshold  = 0.43;

        if ( $args[0] == 'list' ) {
            $inputColor = ( isset($args[2][0]) ) ? $this->assertColor($args[2][0])  : $lightColor;
            $darkColor  = ( isset($args[2][1]) ) ? $this->assertColor($args[2][1])  : $darkColor;
            $lightColor = ( isset($args[2][2]) ) ? $this->assertColor($args[2][2])  : $lightColor;
            if( isset($args[2][3]) ) {
                if( isset($args[2][3][2]) && $args[2][3][2] == '%' ) {
                    $args[2][3][1] /= 100;
                    unset($args[2][3][2]);
                }
                $threshold = $this->assertNumber($args[2][3]);
            }
        }
        else {
            $inputColor  = $this->assertColor($args);
        }

        $inputColor = $this->coerceColor($inputColor);
        $darkColor  = $this->coerceColor($darkColor);
        $lightColor = $this->coerceColor($lightColor);

        //Figure out which is actually light and dark!
        if ( $this->lib_luma($darkColor) > $this->lib_luma($lightColor) ) {
            $t  = $lightColor;
            $lightColor = $darkColor;
            $darkColor  = $t;
        }

        $inputColor_alpha = $this->lib_alpha($inputColor);
        if ( ( $this->lib_luma($inputColor) * $inputColor_alpha) < $threshold) {
            return $lightColor;
        }
        return $darkColor;
    }

    protected function lib_luma($color) {
        $color = $this->coerceColor($color);
        return (0.2126 * $color[1] / 255) + (0.7152 * $color[2] / 255) + (0.0722 * $color[3] / 255);
    }


    public function assertColor($value, $error = "expected color value") {
        $color = $this->coerceColor($value);
        if (is_null($color)) $this->throwError($error);
        return $color;
    }

    public function assertNumber($value, $error = "expecting number") {
        if ($value[0] == "number") return $value[1];
        $this->throwError($error);
    }

    public function assertArgs($value, $expectedArgs, $name="") {
        if ($expectedArgs == 1) {
            return $value;
        } else {
            if ($value[0] !== "list" || $value[1] != ",") $this->throwError("expecting list");
            $values = $value[2];
            $numValues = count($values);
            if ($expectedArgs != $numValues) {
                if ($name) {
                    $name = $name . ": ";
                }

                $this->throwError("{$name}expecting $expectedArgs arguments, got $numValues");
            }

            return $values;
        }
    }

    public function assertMinArgs($value, $expectedMinArgs, $name="") {
        if ($value[0] !== "list" || $value[1] != ",") $this->throwError("expecting list");
        $values = $value[2];
        $numValues = count($values);
        if ($expectedMinArgs > $numValues) {
            if ($name) {
                $name = $name . ": ";
            }

            $this->throwError("{$name}expecting at least $expectedMinArgs arguments, got $numValues");
        }

        return $values;
    }

    protected function toHSL($color) {
        if ($color[0] == 'hsl') return $color;

        $r = $color[1] / 255;
        $g = $color[2] / 255;
        $b = $color[3] / 255;

        $min = min($r, $g, $b);
        $max = max($r, $g, $b);

        $L = ($min + $max) / 2;
        if ($min == $max) {
            $S = $H = 0;
        } else {
            if ($L < 0.5)
                $S = ($max - $min)/($max + $min);
            else
                $S = ($max - $min)/(2.0 - $max - $min);

            if ($r == $max) $H = ($g - $b)/($max - $min);
            elseif ($g == $max) $H = 2.0 + ($b - $r)/($max - $min);
            elseif ($b == $max) $H = 4.0 + ($r - $g)/($max - $min);

        }

        $out = array('hsl',
            ($H < 0 ? $H + 6 : $H)*60,
            $S*100,
            $L*100,
        );

        if (count($color) > 4) $out[] = $color[4]; // copy alpha
        return $out;
    }

    protected function toRGB_helper($comp, $temp1, $temp2) {
        if ($comp < 0) $comp += 1.0;
        elseif ($comp > 1) $comp -= 1.0;

        if (6 * $comp < 1) return $temp1 + ($temp2 - $temp1) * 6 * $comp;
        if (2 * $comp < 1) return $temp2;
        if (3 * $comp < 2) return $temp1 + ($temp2 - $temp1)*((2/3) - $comp) * 6;

        return $temp1;
    }

    /**
     * Converts a hsl array into a color value in rgb.
     * Expects H to be in range of 0 to 360, S and L in 0 to 100
     */
    protected function toRGB($color) {
        if ($color[0] == 'color') return $color;

        $H = $color[1] / 360;
        $S = $color[2] / 100;
        $L = $color[3] / 100;

        if ($S == 0) {
            $r = $g = $b = $L;
        } else {
            $temp2 = $L < 0.5 ?
                $L*(1.0 + $S) :
                $L + $S - $L * $S;

            $temp1 = 2.0 * $L - $temp2;

            $r = $this->toRGB_helper($H + 1/3, $temp1, $temp2);
            $g = $this->toRGB_helper($H, $temp1, $temp2);
            $b = $this->toRGB_helper($H - 1/3, $temp1, $temp2);
        }

        // $out = array('color', round($r*255), round($g*255), round($b*255));
        $out = array('color', $r*255, $g*255, $b*255);
        if (count($color) > 4) $out[] = $color[4]; // copy alpha
        return $out;
    }

    protected function clamp($v, $max = 1, $min = 0) {
        return min($max, max($min, $v));
    }

    /**
     * Convert the rgb, rgba, hsl color literals of function type
     * as returned by the parser into values of color type.
     */
    protected function funcToColor($func) {
        $fname = $func[1];
        if ($func[2][0] != 'list') return false; // need a list of arguments
        $rawComponents = $func[2][2];

        if ($fname == 'hsl' || $fname == 'hsla') {
            $hsl = array('hsl');
            $i = 0;
            foreach ($rawComponents as $c) {
                $val = $this->reduce($c);
                $val = isset($val[1]) ? floatval($val[1]) : 0;

                if ($i == 0) $clamp = 360;
                elseif ($i < 3) $clamp = 100;
                else $clamp = 1;

                $hsl[] = $this->clamp($val, $clamp);
                $i++;
            }

            while (count($hsl) < 4) $hsl[] = 0;
            return $this->toRGB($hsl);

        } elseif ($fname == 'rgb' || $fname == 'rgba') {
            $components = array();
            $i = 1;
            foreach	($rawComponents as $c) {
                $c = $this->reduce($c);
                if ($i < 4) {
                    if ($c[0] == "number" && $c[2] == "%") {
                        $components[] = 255 * ($c[1] / 100);
                    } else {
                        $components[] = floatval($c[1]);
                    }
                } elseif ($i == 4) {
                    if ($c[0] == "number" && $c[2] == "%") {
                        $components[] = 1.0 * ($c[1] / 100);
                    } else {
                        $components[] = floatval($c[1]);
                    }
                } else break;

                $i++;
            }
            while (count($components) < 3) $components[] = 0;
            array_unshift($components, 'color');
            return $this->fixColor($components);
        }

        return false;
    }

    protected function reduce($value, $forExpression = false) {
        switch ($value[0]) {
            case "interpolate":
                $reduced = $this->reduce($value[1]);
                $var = $this->compileValue($reduced);
                $res = $this->reduce(array("variable", $this->vPrefix . $var));

                if ($res[0] == "raw_color") {
                    $res = $this->coerceColor($res);
                }

                if (empty($value[2])) $res = $this->lib_e($res);

                return $res;
            case "variable":
                $key = $value[1];
                if (is_array($key)) {
                    $key = $this->reduce($key);
                    $key = $this->vPrefix . $this->compileValue($this->lib_e($key));
                }

                $seen =& $this->env->seenNames;

                if (!empty($seen[$key])) {
                    $this->throwError("infinite loop detected: $key");
                }

                $seen[$key] = true;
                $out = $this->reduce($this->get($key));
                $seen[$key] = false;
                return $out;
            case "list":
                foreach ($value[2] as &$item) {
                    $item = $this->reduce($item, $forExpression);
                }
                return $value;
            case "expression":
                return $this->evaluate($value);
            case "string":
                foreach ($value[2] as &$part) {
                    if (is_array($part)) {
                        $strip = $part[0] == "variable";
                        $part = $this->reduce($part);
                        if ($strip) $part = $this->lib_e($part);
                    }
                }
                return $value;
            case "escape":
                [,$inner] = $value;
                return $this->lib_e($this->reduce($inner));
            case "function":
                $color = $this->funcToColor($value);
                if ($color) return $color;

                [, $name, $args] = $value;
                if ($name == "%") $name = "_sprintf";

                $f = isset($this->libFunctions[$name]) ?
                    $this->libFunctions[$name] : array($this, 'lib_'.str_replace('-', '_', $name));

                if (is_callable($f)) {
                    if ($args[0] == 'list')
                        $args = self::compressList($args[2], $args[1]);

                    $ret = call_user_func($f, $this->reduce($args, true), $this);

                    if (is_null($ret)) {
                        return array("string", "", array(
                            $name, "(", $args, ")"
                        ));
                    }

                    // convert to a typed value if the result is a php primitive
                    if (is_numeric($ret)) $ret = array('number', $ret, "");
                    elseif (!is_array($ret)) $ret = array('keyword', $ret);

                    return $ret;
                }

                // plain function, reduce args
                $value[2] = $this->reduce($value[2]);
                return $value;
            case "unary":
                [, $op, $exp] = $value;
                $exp = $this->reduce($exp);

                if ($exp[0] == "number") {
                    switch ($op) {
                        case "+":
                            return $exp;
                        case "-":
                            $exp[1] *= -1;
                            return $exp;
                    }
                }
                return array("string", "", array($op, $exp));
        }

        if ($forExpression) {
            switch ($value[0]) {
                case "keyword":
                    if ($color = $this->coerceColor($value)) {
                        return $color;
                    }
                    break;
                case "raw_color":
                    return $this->coerceColor($value);
            }
        }

        return $value;
    }


    // coerce a value for use in color operation
    protected function coerceColor($value) {
        switch($value[0]) {
            case 'color': return $value;
            case 'raw_color':
                $c = array("color", 0, 0, 0);
                $colorStr = substr($value[1], 1);
                $num = hexdec($colorStr);
                $width = strlen($colorStr) == 3 ? 16 : 256;

                for ($i = 3; $i > 0; $i--) { // 3 2 1
                    $t = $num % $width;
                    $num /= $width;

                    $c[$i] = $t * (256/$width) + $t * floor(16/$width);
                }

                return $c;
            case 'keyword':
                $name = $value[1];
                if (isset(self::$cssColors[$name])) {
                    $rgba = explode(',', self::$cssColors[$name]);

                    if(isset($rgba[3]))
                        return array('color', $rgba[0], $rgba[1], $rgba[2], $rgba[3]);

                    return array('color', $rgba[0], $rgba[1], $rgba[2]);
                }
                return null;
        }
    }

    // make something string like into a string
    protected function coerceString($value) {
        switch ($value[0]) {
            case "string":
                return $value;
            case "keyword":
                return array("string", "", array($value[1]));
        }
        return null;
    }

    // turn list of length 1 into value type
    protected function flattenList($value) {
        if ($value[0] == "list" && count($value[2]) == 1) {
            return $this->flattenList($value[2][0]);
        }
        return $value;
    }

    public function toBool($a) {
        if ($a) return self::$TRUE;
        else return self::$FALSE;
    }

    // evaluate an expression
    protected function evaluate($exp) {
        [, $op, $left, $right, $whiteBefore, $whiteAfter] = $exp;

        $left = $this->reduce($left, true);
        $right = $this->reduce($right, true);

        if ($leftColor = $this->coerceColor($left)) {
            $left = $leftColor;
        }

        if ($rightColor = $this->coerceColor($right)) {
            $right = $rightColor;
        }

        $ltype = $left[0];
        $rtype = $right[0];

        // operators that work on all types
        if ($op == "and") {
            return $this->toBool($left == self::$TRUE && $right == self::$TRUE);
        }

        if ($op == "=") {
            return $this->toBool($this->eq($left, $right) );
        }

        if ($op == "+" && !is_null($str = $this->stringConcatenate($left, $right))) {
            return $str;
        }

        // type based operators
        $fname = "op_{$ltype}_{$rtype}";
        if (is_callable(array($this, $fname))) {
            $out = $this->$fname($op, $left, $right);
            if (!is_null($out)) return $out;
        }

        // make the expression look it did before being parsed
        $paddedOp = $op;
        if ($whiteBefore) $paddedOp = " " . $paddedOp;
        if ($whiteAfter) $paddedOp .= " ";

        return array("string", "", array($left, $paddedOp, $right));
    }

    protected function stringConcatenate($left, $right) {
        if ($strLeft = $this->coerceString($left)) {
            if ($right[0] == "string") {
                $right[1] = "";
            }
            $strLeft[2][] = $right;
            return $strLeft;
        }

        if ($strRight = $this->coerceString($right)) {
            array_unshift($strRight[2], $left);
            return $strRight;
        }
    }

    protected function convert( $number, $to )
    {
        $value = $this->assertNumber( $number );
        $from = $number[2];

        // easy out
        if( $from == $to )
            return $number;

        // check if the from value is a length
        if( ( $from_index = array_search( $from, self::$lengths ) ) !== false ) {
            // make sure to value is too
            if( in_array( $to, self::$lengths ) ) {
                // do the actual conversion
                $to_index = array_search( $to, self::$lengths );
                $px = $value * self::$lengths_to_base[ $from_index ];
                $result = $px * ( 1 / self::$lengths_to_base[ $to_index ] );

                $result = round( $result, 8 );
                return array( "number", $result, $to );
            }
        }

        // do the same check for times
        if( in_array( $from, self::$times ) ) {
            if( in_array( $to, self::$times ) ) {
                // currently only ms and s are valid
                if( $to == "ms" )
                    $result = $value * 1000;
                else
                    $result = $value / 1000;

                $result = round( $result, 8 );
                return array( "number", $result, $to );
            }
        }

        // lastly check for an angle
        if( in_array( $from, self::$angles ) ) {
            // convert whatever angle it is into degrees
            if( $from == "rad" )
                $deg = rad2deg( $value );

            else if( $from == "turn" )
                $deg = $value * 360;

            else if( $from == "grad" )
                $deg = $value / (400 / 360);

            else
                $deg = $value;

            // Then convert it from degrees into desired unit
            if( $to == "deg" )
                $result = $deg;

            if( $to == "rad" )
                $result = deg2rad( $deg );

            if( $to == "turn" )
                $result = $value / 360;

            if( $to == "grad" )
                $result = $value * (400 / 360);

            $result = round( $result, 8 );
            return array( "number", $result, $to );
        }

        // we don't know how to convert these
        $this->throwError( "Cannot convert {$from} to {$to}" );
    }

    // make sure a color's components don't go out of bounds
    protected function fixColor($c) {
        foreach (range(1, 3) as $i) {
            if ($c[$i] < 0) $c[$i] = 0;
            if ($c[$i] > 255) $c[$i] = 255;
        }

        return $c;
    }

    protected function op_number_color($op, $lft, $rgt) {
        if ($op == '+' || $op == '*') {
            return $this->op_color_number($op, $rgt, $lft);
        }
    }

    protected function op_color_number($op, $lft, $rgt) {
        if ($rgt[0] == '%') $rgt[1] /= 100;

        return $this->op_color_color($op, $lft,
            array_fill(1, count($lft) - 1, $rgt[1]));
    }

    protected function op_color_color($op, $left, $right) {
        $out = array('color');
        $max = count($left) > count($right) ? count($left) : count($right);
        foreach (range(1, $max - 1) as $i) {
            $lval = isset($left[$i]) ? $left[$i] : 0;
            $rval = isset($right[$i]) ? $right[$i] : 0;
            switch ($op) {
                case '+':
                    $out[] = $lval + $rval;
                    break;
                case '-':
                    $out[] = $lval - $rval;
                    break;
                case '*':
                    $out[] = $lval * $rval;
                    break;
                case '%':
                    $out[] = $lval % $rval;
                    break;
                case '/':
                    if ($rval == 0) $this->throwError("evaluate error: can't divide by zero");
                    $out[] = $lval / $rval;
                    break;
                default:
                    $this->throwError('evaluate error: color op number failed on op '.$op);
            }
        }
        return $this->fixColor($out);
    }

    function lib_red($color){
        $color = $this->coerceColor($color);
        if (is_null($color)) {
            $this->throwError('color expected for red()');
        }

        return $color[1];
    }

    function lib_green($color){
        $color = $this->coerceColor($color);
        if (is_null($color)) {
            $this->throwError('color expected for green()');
        }

        return $color[2];
    }

    function lib_blue($color){
        $color = $this->coerceColor($color);
        if (is_null($color)) {
            $this->throwError('color expected for blue()');
        }

        return $color[3];
    }


    // operator on two numbers
    protected function op_number_number($op, $left, $right) {
        $unit = empty($left[2]) ? $right[2] : $left[2];

        $value = 0;
        switch ($op) {
            case '+':
                $value = $left[1] + $right[1];
                break;
            case '*':
                $value = $left[1] * $right[1];
                break;
            case '-':
                $value = $left[1] - $right[1];
                break;
            case '%':
                $value = $left[1] % $right[1];
                break;
            case '/':
                if ($right[1] == 0) $this->throwError('parse error: divide by zero');
                $value = $left[1] / $right[1];
                break;
            case '<':
                return $this->toBool($left[1] < $right[1]);
            case '>':
                return $this->toBool($left[1] > $right[1]);
            case '>=':
                return $this->toBool($left[1] >= $right[1]);
            case '=<':
                return $this->toBool($left[1] <= $right[1]);
            default:
                $this->throwError('parse error: unknown number operator: '.$op);
        }

        return array("number", $value, $unit);
    }


    /* environment functions */

    protected function makeOutputBlock($type, $selectors = null) {
        $b = new stdclass;
        $b->lines = array();
        $b->children = array();
        $b->selectors = $selectors;
        $b->type = $type;
        $b->parent = $this->scope;
        return $b;
    }

    // the state of execution
    protected function pushEnv($block = null) {
        $e = new stdclass;
        $e->parent = $this->env;
        $e->store = array();
        $e->block = $block;

        $this->env = $e;
        return $e;
    }

    // pop something off the stack
    protected function popEnv() {
        $old = $this->env;
        $this->env = $this->env->parent;
        return $old;
    }

    // set something in the current env
    protected function set($name, $value) {
        $this->env->store[$name] = $value;
    }


    // get the highest occurrence entry for a name
    protected function get($name) {
        $current = $this->env;

        // track scope to evaluate
        $scope_secondary = array();

        $isArguments = $name == $this->vPrefix . 'arguments';
        while ($current) {
            if ($isArguments && isset($current->arguments)) {
                return array('list', ' ', $current->arguments);
            }

            if (isset($current->store[$name]))
                return $current->store[$name];
            // has secondary scope?
            if (isset($current->storeParent))
                $scope_secondary[] = $current->storeParent;

            if (isset($current->parent))
                $current = $current->parent;
            else
                $current = null;
        }

        while (count($scope_secondary)) {
            // pop one off
            $current = array_shift($scope_secondary);
            while ($current) {
                if ($isArguments && isset($current->arguments)) {
                    return array('list', ' ', $current->arguments);
                }

                if (isset($current->store[$name])) {
                    return $current->store[$name];
                }

                // has secondary scope?
                if (isset($current->storeParent)) {
                    $scope_secondary[] = $current->storeParent;
                }

                if (isset($current->parent)) {
                    $current = $current->parent;
                } else {
                    $current = null;
                }
            }
        }

        $this->throwError("variable $name is undefined");
    }

    // inject array of unparsed strings into environment as variables
    protected function injectVariables($args) {
        $this->pushEnv();
        $parser = new lessc_parser($this, __METHOD__);
        foreach ($args as $name => $strValue) {
            if ($name[0] != '@') $name = '@'.$name;
            $parser->count = 0;
            $parser->buffer = (string)$strValue;
            if (!$parser->propertyValue($value)) {
                throw new \Exception("failed to parse passed in variable $name: $strValue");
            }

            $this->set($name, $value);
        }
    }

    /**
     * Initialize any static state, can initialize parser for a file
     * $opts isn't used yet
     */
    public function __construct($fname = null) {
        if ($fname !== null) {
            // used for deprecated parse method
            $this->_parseFile = $fname;
        }
    }

    public function compile($string, $name = null) {
        $locale = setlocale(LC_NUMERIC, 0);
        setlocale(LC_NUMERIC, "C");

        $this->parser = $this->makeParser($name);
        $root = $this->parser->parse($string);

        $this->env = null;
        $this->scope = null;
        $this->allParsedFiles = array();

        $this->formatter = $this->newFormatter();

        if (!empty($this->registeredVars)) {
            $this->injectVariables($this->registeredVars);
        }

        $this->sourceParser = $this->parser; // used for error messages
        $this->compileBlock($root);

        ob_start();
        $this->formatter->block($this->scope);
        $out = ob_get_clean();
        setlocale(LC_NUMERIC, $locale);
        return $out;
    }

    public function compileFile($fname, $outFname = null) {
        if (!is_readable($fname)) {
            throw new \Exception('load error: failed to find '.$fname);
        }

        $pi = pathinfo($fname);

        $oldImport = $this->importDir;

        $this->importDir = (array)$this->importDir;
        $this->importDir[] = $pi['dirname'].'/';

        $this->addParsedFile($fname);

        $out = $this->compile(file_get_contents($fname), $fname);

        $this->importDir = $oldImport;

        if ($outFname !== null) {
            return file_put_contents($outFname, $out);
        }

        return $out;
    }

    /**
     * Based on explicit input/output files does a full change check on cache before compiling.
     *
     * @param string $in
     * @param string $out
     * @param boolean $force
     * @return string Compiled CSS results
     * @throws Exception
     */
    public function checkedCachedCompile($in, $out, $force = false) {
        if (!is_file($in) || !is_readable($in)) {
            throw new Exception('Invalid or unreadable input file specified.');
        }
        if (is_dir($out) || !is_writable(file_exists($out) ? $out : dirname($out))) {
            throw new Exception('Invalid or unwritable output file specified.');
        }

        $outMeta = $out . '.meta';
        $metadata = null;
        if (!$force && is_file($outMeta)) {
            $metadata = unserialize(file_get_contents($outMeta));
        }

        $output = $this->cachedCompile($metadata ? $metadata : $in);

        if (!$metadata || $metadata['updated'] != $output['updated']) {
            $css = $output['compiled'];
            unset($output['compiled']);
            file_put_contents($out, $css);
            file_put_contents($outMeta, serialize($output));
        } else {
            $css = file_get_contents($out);
        }

        return $css;
    }

    // compile only if changed input has changed or output doesn't exist
    public function checkedCompile($in, $out) {
        if (!is_file($out) || filemtime($in) > filemtime($out)) {
            $this->compileFile($in, $out);
            return true;
        }
        return false;
    }

    /**
     * Execute lessphp on a .less file or a lessphp cache structure
     *
     * The lessphp cache structure contains information about a specific
     * less file having been parsed. It can be used as a hint for future
     * calls to determine whether or not a rebuild is required.
     *
     * The cache structure contains two important keys that may be used
     * externally:
     *
     * compiled: The final compiled CSS
     * updated: The time (in seconds) the CSS was last compiled
     *
     * The cache structure is a plain-ol' PHP associative array and can
     * be serialized and unserialized without a hitch.
     *
     * @param mixed $in Input
     * @param bool $force Force rebuild?
     * @return array lessphp cache structure
     */
    public function cachedCompile($in, $force = false) {
        // assume no root
        $root = null;

        if (is_string($in)) {
            $root = $in;
        } elseif (is_array($in) and isset($in['root'])) {
            if ($force or ! isset($in['files'])) {
                // If we are forcing a recompile or if for some reason the
                // structure does not contain any file information we should
                // specify the root to trigger a rebuild.
                $root = $in['root'];
            } elseif (isset($in['files']) and is_array($in['files'])) {
                foreach ($in['files'] as $fname => $ftime ) {
                    if (!file_exists($fname) or filemtime($fname) > $ftime) {
                        // One of the files we knew about previously has changed
                        // so we should look at our incoming root again.
                        $root = $in['root'];
                        break;
                    }
                }
            }
        } else {
            // TODO: Throw an exception? We got neither a string nor something
            // that looks like a compatible lessphp cache structure.
            return null;
        }

        if ($root !== null) {
            // If we have a root value which means we should rebuild.
            $out = array();
            $out['root'] = $root;
            $out['compiled'] = $this->compileFile($root);
            $out['files'] = $this->allParsedFiles();
            $out['updated'] = time();
            return $out;
        } else {
            // No changes, pass back the structure
            // we were given initially.
            return $in;
        }

    }

    // parse and compile buffer
    // This is deprecated
    public function parse($str = null, $initialVariables = null) {
        if (is_array($str)) {
            $initialVariables = $str;
            $str = null;
        }

        $oldVars = $this->registeredVars;
        if ($initialVariables !== null) {
            $this->setVariables($initialVariables);
        }

        if ($str == null) {
            if (empty($this->_parseFile)) {
                throw new \Exception("nothing to parse");
            }

            $out = $this->compileFile($this->_parseFile);
        } else {
            $out = $this->compile($str);
        }

        $this->registeredVars = $oldVars;
        return $out;
    }

    protected function makeParser($name) {
        $parser = new lessc_parser($this, $name);
        $parser->writeComments = $this->preserveComments;

        return $parser;
    }

    public function setFormatter($name) {
        $this->formatterName = $name;
    }

    protected function newFormatter() {
        $className = "lessc_formatter_lessjs";
        if (!empty($this->formatterName)) {
            if (!is_string($this->formatterName))
                return $this->formatterName;
            $className = "lessc_formatter_$this->formatterName";
        }

        return new $className;
    }

    public function setPreserveComments($preserve) {
        $this->preserveComments = $preserve;
    }

    public function registerFunction($name, $func) {
        $this->libFunctions[$name] = $func;
    }

    public function unregisterFunction($name) {
        unset($this->libFunctions[$name]);
    }

    public function setVariables($variables) {
        $this->registeredVars = array_merge($this->registeredVars, $variables);
    }

    public function unsetVariable($name) {
        unset($this->registeredVars[$name]);
    }

    public function setImportDir($dirs) {
        $this->importDir = (array)$dirs;
    }

    public function addImportDir($dir) {
        $this->importDir = (array)$this->importDir;
        $this->importDir[] = $dir;
    }

    public function allParsedFiles() {
        return $this->allParsedFiles;
    }

    public function addParsedFile($file) {
        $this->allParsedFiles[realpath($file)] = filemtime($file);
    }

    /**
     * Uses the current value of $this->count to show line and line number
     */
    public function throwError($msg = null) {
        if ($this->sourceLoc >= 0) {
            $this->sourceParser->throwError($msg, $this->sourceLoc);
        }
        throw new \Exception($msg);
    }

    // compile file $in to file $out if $in is newer than $out
    // returns true when it compiles, false otherwise
    public static function ccompile($in, $out, $less = null) {
        if ($less === null) {
            $less = new self;
        }
        return $less->checkedCompile($in, $out);
    }

    public static function cexecute($in, $force = false, $less = null) {
        if ($less === null) {
            $less = new self;
        }
        return $less->cachedCompile($in, $force);
    }

    static protected $cssColors = array(
        'aliceblue' => '240,248,255',
        'antiquewhite' => '250,235,215',
        'aqua' => '0,255,255',
        'aquamarine' => '127,255,212',
        'azure' => '240,255,255',
        'beige' => '245,245,220',
        'bisque' => '255,228,196',
        'black' => '0,0,0',
        'blanchedalmond' => '255,235,205',
        'blue' => '0,0,255',
        'blueviolet' => '138,43,226',
        'brown' => '165,42,42',
        'burlywood' => '222,184,135',
        'cadetblue' => '95,158,160',
        'chartreuse' => '127,255,0',
        'chocolate' => '210,105,30',
        'coral' => '255,127,80',
        'cornflowerblue' => '100,149,237',
        'cornsilk' => '255,248,220',
        'crimson' => '220,20,60',
        'cyan' => '0,255,255',
        'darkblue' => '0,0,139',
        'darkcyan' => '0,139,139',
        'darkgoldenrod' => '184,134,11',
        'darkgray' => '169,169,169',
        'darkgreen' => '0,100,0',
        'darkgrey' => '169,169,169',
        'darkkhaki' => '189,183,107',
        'darkmagenta' => '139,0,139',
        'darkolivegreen' => '85,107,47',
        'darkorange' => '255,140,0',
        'darkorchid' => '153,50,204',
        'darkred' => '139,0,0',
        'darksalmon' => '233,150,122',
        'darkseagreen' => '143,188,143',
        'darkslateblue' => '72,61,139',
        'darkslategray' => '47,79,79',
        'darkslategrey' => '47,79,79',
        'darkturquoise' => '0,206,209',
        'darkviolet' => '148,0,211',
        'deeppink' => '255,20,147',
        'deepskyblue' => '0,191,255',
        'dimgray' => '105,105,105',
        'dimgrey' => '105,105,105',
        'dodgerblue' => '30,144,255',
        'firebrick' => '178,34,34',
        'floralwhite' => '255,250,240',
        'forestgreen' => '34,139,34',
        'fuchsia' => '255,0,255',
        'gainsboro' => '220,220,220',
        'ghostwhite' => '248,248,255',
        'gold' => '255,215,0',
        'goldenrod' => '218,165,32',
        'gray' => '128,128,128',
        'green' => '0,128,0',
        'greenyellow' => '173,255,47',
        'grey' => '128,128,128',
        'honeydew' => '240,255,240',
        'hotpink' => '255,105,180',
        'indianred' => '205,92,92',
        'indigo' => '75,0,130',
        'ivory' => '255,255,240',
        'khaki' => '240,230,140',
        'lavender' => '230,230,250',
        'lavenderblush' => '255,240,245',
        'lawngreen' => '124,252,0',
        'lemonchiffon' => '255,250,205',
        'lightblue' => '173,216,230',
        'lightcoral' => '240,128,128',
        'lightcyan' => '224,255,255',
        'lightgoldenrodyellow' => '250,250,210',
        'lightgray' => '211,211,211',
        'lightgreen' => '144,238,144',
        'lightgrey' => '211,211,211',
        'lightpink' => '255,182,193',
        'lightsalmon' => '255,160,122',
        'lightseagreen' => '32,178,170',
        'lightskyblue' => '135,206,250',
        'lightslategray' => '119,136,153',
        'lightslategrey' => '119,136,153',
        'lightsteelblue' => '176,196,222',
        'lightyellow' => '255,255,224',
        'lime' => '0,255,0',
        'limegreen' => '50,205,50',
        'linen' => '250,240,230',
        'magenta' => '255,0,255',
        'maroon' => '128,0,0',
        'mediumaquamarine' => '102,205,170',
        'mediumblue' => '0,0,205',
        'mediumorchid' => '186,85,211',
        'mediumpurple' => '147,112,219',
        'mediumseagreen' => '60,179,113',
        'mediumslateblue' => '123,104,238',
        'mediumspringgreen' => '0,250,154',
        'mediumturquoise' => '72,209,204',
        'mediumvioletred' => '199,21,133',
        'midnightblue' => '25,25,112',
        'mintcream' => '245,255,250',
        'mistyrose' => '255,228,225',
        'moccasin' => '255,228,181',
        'navajowhite' => '255,222,173',
        'navy' => '0,0,128',
        'oldlace' => '253,245,230',
        'olive' => '128,128,0',
        'olivedrab' => '107,142,35',
        'orange' => '255,165,0',
        'orangered' => '255,69,0',
        'orchid' => '218,112,214',
        'palegoldenrod' => '238,232,170',
        'palegreen' => '152,251,152',
        'paleturquoise' => '175,238,238',
        'palevioletred' => '219,112,147',
        'papayawhip' => '255,239,213',
        'peachpuff' => '255,218,185',
        'peru' => '205,133,63',
        'pink' => '255,192,203',
        'plum' => '221,160,221',
        'powderblue' => '176,224,230',
        'purple' => '128,0,128',
        'red' => '255,0,0',
        'rosybrown' => '188,143,143',
        'royalblue' => '65,105,225',
        'saddlebrown' => '139,69,19',
        'salmon' => '250,128,114',
        'sandybrown' => '244,164,96',
        'seagreen' => '46,139,87',
        'seashell' => '255,245,238',
        'sienna' => '160,82,45',
        'silver' => '192,192,192',
        'skyblue' => '135,206,235',
        'slateblue' => '106,90,205',
        'slategray' => '112,128,144',
        'slategrey' => '112,128,144',
        'snow' => '255,250,250',
        'springgreen' => '0,255,127',
        'steelblue' => '70,130,180',
        'tan' => '210,180,140',
        'teal' => '0,128,128',
        'thistle' => '216,191,216',
        'tomato' => '255,99,71',
        'transparent' => '0,0,0,0',
        'turquoise' => '64,224,208',
        'violet' => '238,130,238',
        'wheat' => '245,222,179',
        'white' => '255,255,255',
        'whitesmoke' => '245,245,245',
        'yellow' => '255,255,0',
        'yellowgreen' => '154,205,50'
    );
}

// responsible for taking a string of LESS code and converting it into a
// syntax tree
class lessc_parser {
    static protected $nextBlockId = 0; // used to uniquely identify blocks

    static protected $precedence = array(
        '=<' => 0,
        '>=' => 0,
        '=' => 0,
        '<' => 0,
        '>' => 0,

        '+' => 1,
        '-' => 1,
        '*' => 2,
        '/' => 2,
        '%' => 2,
    );

    static protected $whitePattern;
    static protected $commentMulti;

    static protected $commentSingle = "//";
    static protected $commentMultiLeft = "/*";
    static protected $commentMultiRight = "*/";

    // regex string to match any of the operators
    static protected $operatorString;

    // these properties will supress division unless it's inside parenthases
    static protected $supressDivisionProps =
        array('/border-radius$/i', '/^font$/i');

    protected $blockDirectives = array("font-face", "keyframes", "page", "-moz-document", "viewport", "-moz-viewport", "-o-viewport", "-ms-viewport");
    protected $lineDirectives = array("charset");

    /**
     * if we are in parens we can be more liberal with whitespace around
     * operators because it must evaluate to a single value and thus is less
     * ambiguous.
     *
     * Consider:
     *     property1: 10 -5; // is two numbers, 10 and -5
     *     property2: (10 -5); // should evaluate to 5
     */
    protected $inParens = false;

    // caches preg escaped literals
    static protected $literalCache = array();

    protected $eatWhiteDefault;
    protected $lessc;
    protected $sourceName;
    public $writeComments;
    public $count;
    protected $line;
    protected $env;
    public $buffer;
    protected $seenComments;
    protected $inExp;


    public function __construct($lessc, $sourceName = null) {
        $this->eatWhiteDefault = true;
        // reference to less needed for vPrefix, mPrefix, and parentSelector
        $this->lessc = $lessc;

        $this->sourceName = $sourceName; // name used for error messages

        $this->writeComments = false;

        if (!self::$operatorString) {
            self::$operatorString =
                '('.implode('|', array_map(array('lessc', 'preg_quote'),
                    array_keys(self::$precedence))).')';

            $commentSingle = lessc::preg_quote(self::$commentSingle);
            $commentMultiLeft = lessc::preg_quote(self::$commentMultiLeft);
            $commentMultiRight = lessc::preg_quote(self::$commentMultiRight);

            self::$commentMulti = $commentMultiLeft.'.*?'.$commentMultiRight;
            self::$whitePattern = '/'.$commentSingle.'[^\n]*\s*|('.self::$commentMulti.')\s*|\s+/Ais';
        }
    }

    public function parse($buffer) {
        $this->count = 0;
        $this->line = 1;

        $this->env = null; // block stack
        $this->buffer = $this->writeComments ? $buffer : $this->removeComments($buffer);
        $this->pushSpecialBlock("root");
        $this->eatWhiteDefault = true;
        $this->seenComments = array();

        // trim whitespace on head
        // if (preg_match('/^\s+/', $this->buffer, $m)) {
        // 	$this->line += substr_count($m[0], "\n");
        // 	$this->buffer = ltrim($this->buffer);
        // }
        $this->whitespace();

        // parse the entire file
        while (false !== $this->parseChunk());

        if ($this->count != strlen($this->buffer))
            $this->throwError();

        // TODO report where the block was opened
        if ( !property_exists($this->env, 'parent') || !is_null($this->env->parent) )
            throw new \Exception('parse error: unclosed block');

        return $this->env;
    }

    /**
     * Parse a single chunk off the head of the buffer and append it to the
     * current parse environment.
     * Returns false when the buffer is empty, or when there is an error.
     *
     * This function is called repeatedly until the entire document is
     * parsed.
     *
     * This parser is most similar to a recursive descent parser. Single
     * functions represent discrete grammatical rules for the language, and
     * they are able to capture the text that represents those rules.
     *
     * Consider the function lessc::keyword(). (all parse functions are
     * structured the same)
     *
     * The function takes a single reference argument. When calling the
     * function it will attempt to match a keyword on the head of the buffer.
     * If it is successful, it will place the keyword in the referenced
     * argument, advance the position in the buffer, and return true. If it
     * fails then it won't advance the buffer and it will return false.
     *
     * All of these parse functions are powered by lessc::match(), which behaves
     * the same way, but takes a literal regular expression. Sometimes it is
     * more convenient to use match instead of creating a new function.
     *
     * Because of the format of the functions, to parse an entire string of
     * grammatical rules, you can chain them together using &&.
     *
     * But, if some of the rules in the chain succeed before one fails, then
     * the buffer position will be left at an invalid state. In order to
     * avoid this, lessc::seek() is used to remember and set buffer positions.
     *
     * Before parsing a chain, use $s = $this->seek() to remember the current
     * position into $s. Then if a chain fails, use $this->seek($s) to
     * go back where we started.
     */
    protected function parseChunk() {
        if (empty($this->buffer)) return false;
        $s = $this->seek();

        if ($this->whitespace()) {
            return true;
        }

        // setting a property
        if ($this->keyword($key) && $this->assign() &&
            $this->propertyValue($value, $key) && $this->end())
        {
            $this->append(array('assign', $key, $value), $s);
            return true;
        } else {
            $this->seek($s);
        }


        // look for special css blocks
        if ($this->literal('@', false)) {
            $this->count--;

            // media
            if ($this->literal('@media')) {
                if (($this->mediaQueryList($mediaQueries) || true)
                    && $this->literal('{'))
                {
                    $media = $this->pushSpecialBlock("media");
                    $media->queries = is_null($mediaQueries) ? array() : $mediaQueries;
                    return true;
                } else {
                    $this->seek($s);
                    return false;
                }
            }

            if ($this->literal("@", false) && $this->keyword($dirName)) {
                if ($this->isDirective($dirName, $this->blockDirectives)) {
                    if (($this->openString("{", $dirValue, null, array(";")) || true) &&
                        $this->literal("{"))
                    {
                        $dir = $this->pushSpecialBlock("directive");
                        $dir->name = $dirName;
                        if (isset($dirValue)) $dir->value = $dirValue;
                        return true;
                    }
                } elseif ($this->isDirective($dirName, $this->lineDirectives)) {
                    if ($this->propertyValue($dirValue) && $this->end()) {
                        $this->append(array("directive", $dirName, $dirValue));
                        return true;
                    }
                } elseif ($this->literal(":", true)) {
                    //Ruleset Definition
                    if (($this->openString("{", $dirValue, null, array(";")) || true) &&
                        $this->literal("{"))
                    {
                        $dir = $this->pushBlock($this->fixTags(array("@".$dirName)));
                        $dir->name = $dirName;
                        if (isset($dirValue)) $dir->value = $dirValue;
                        return true;
                    }
                }
            }

            $this->seek($s);
        }

        // setting a variable
        if ($this->variable($var) && $this->assign() &&
            $this->propertyValue($value) && $this->end())
        {
            $this->append(array('assign', $var, $value), $s);
            return true;
        } else {
            $this->seek($s);
        }

        if ($this->import($importValue)) {
            $this->append($importValue, $s);
            return true;
        }

        // opening parametric mixin
        if ($this->tag($tag, true) && $this->argumentDef($args, $isVararg) &&
            ($this->guards($guards) || true) &&
            $this->literal('{'))
        {
            $block = $this->pushBlock($this->fixTags(array($tag)));
            $block->args = $args;
            $block->isVararg = $isVararg;
            if (!empty($guards)) $block->guards = $guards;
            return true;
        } else {
            $this->seek($s);
        }

        // opening a simple block
        if ($this->tags($tags) && $this->literal('{', false)) {
            $tags = $this->fixTags($tags);
            $this->pushBlock($tags);
            return true;
        } else {
            $this->seek($s);
        }

        // closing a block
        if ($this->literal('}', false)) {
            try {
                $block = $this->pop();
            } catch (\Exception $e) {
                $this->seek($s);
                $this->throwError($e->getMessage());
            }

            $hidden = false;
            if (is_null($block->type)) {
                $hidden = true;
                if (!isset($block->args)) {
                    foreach ($block->tags as $tag) {
                        if (!is_string($tag) || $tag[0] != $this->lessc->mPrefix) {
                            $hidden = false;
                            break;
                        }
                    }
                }

                foreach ($block->tags as $tag) {
                    if (is_string($tag)) {
                        $this->env->children[$tag][] = $block;
                    }
                }
            }

            if (!$hidden) {
                $this->append(array('block', $block), $s);
            }

            // this is done here so comments aren't bundled into he block that
            // was just closed
            $this->whitespace();
            return true;
        }

        // mixin
        if ($this->mixinTags($tags) &&
            ($this->argumentDef($argv, $isVararg) || true) &&
            ($this->keyword($suffix) || true) && $this->end())
        {
            $tags = $this->fixTags($tags);
            $this->append(array('mixin', $tags, $argv, $suffix), $s);
            return true;
        } else {
            $this->seek($s);
        }

        // spare ;
        if ($this->literal(';')) return true;

        return false; // got nothing, throw error
    }

    protected function isDirective($dirname, $directives) {
        // TODO: cache pattern in parser
        $pattern = implode("|",
            array_map(array("lessc", "preg_quote"), $directives));
        $pattern = '/^(-[a-z-]+-)?(' . $pattern . ')$/i';

        return preg_match($pattern, $dirname);
    }

    protected function fixTags($tags) {
        // move @ tags out of variable namespace
        foreach ($tags as &$tag) {
            if ($tag[0] == $this->lessc->vPrefix)
                $tag[0] = $this->lessc->mPrefix;
        }
        return $tags;
    }

    // a list of expressions
    protected function expressionList(&$exps) {
        $values = array();

        while ($this->expression($exp)) {
            $values[] = $exp;
        }

        if (count($values) == 0) return false;

        $exps = lessc::compressList($values, ' ');
        return true;
    }

    /**
     * Attempt to consume an expression.
     * @link http://en.wikipedia.org/wiki/Operator-precedence_parser#Pseudo-code
     */
    protected function expression(&$out) {
        if ($this->value($lhs)) {
            $out = $this->expHelper($lhs, 0);

            // look for / shorthand
            if (!empty($this->env->supressedDivision)) {
                unset($this->env->supressedDivision);
                $s = $this->seek();
                if ($this->literal("/") && $this->value($rhs)) {
                    $out = array("list", "",
                        array($out, array("keyword", "/"), $rhs));
                } else {
                    $this->seek($s);
                }
            }

            return true;
        }
        return false;
    }

    /**
     * recursively parse infix equation with $lhs at precedence $minP
     */
    protected function expHelper($lhs, $minP) {
        $this->inExp = true;
        $ss = $this->seek();

        while (true) {
            $whiteBefore = isset($this->buffer[$this->count - 1]) &&
                ctype_space($this->buffer[$this->count - 1]);

            // If there is whitespace before the operator, then we require
            // whitespace after the operator for it to be an expression
            $needWhite = $whiteBefore && !$this->inParens;

            if ($this->match(self::$operatorString.($needWhite ? '\s' : ''), $m) && self::$precedence[$m[1]] >= $minP) {
                if (!$this->inParens && isset($this->env->currentProperty) && $m[1] == "/" && empty($this->env->supressedDivision)) {
                    foreach (self::$supressDivisionProps as $pattern) {
                        if (preg_match($pattern, $this->env->currentProperty)) {
                            $this->env->supressedDivision = true;
                            break 2;
                        }
                    }
                }


                $whiteAfter = isset($this->buffer[$this->count - 1]) &&
                    ctype_space($this->buffer[$this->count - 1]);

                if (!$this->value($rhs)) break;

                // peek for next operator to see what to do with rhs
                if ($this->peek(self::$operatorString, $next) && self::$precedence[$next[1]] > self::$precedence[$m[1]]) {
                    $rhs = $this->expHelper($rhs, self::$precedence[$next[1]]);
                }

                $lhs = array('expression', $m[1], $lhs, $rhs, $whiteBefore, $whiteAfter);
                $ss = $this->seek();

                continue;
            }

            break;
        }

        $this->seek($ss);

        return $lhs;
    }

    // consume a list of values for a property
    public function propertyValue(&$value, $keyName = null) {
        $values = array();

        if ($keyName !== null) $this->env->currentProperty = $keyName;

        $s = null;
        while ($this->expressionList($v)) {
            $values[] = $v;
            $s = $this->seek();
            if (!$this->literal(',')) break;
        }

        if ($s) $this->seek($s);

        if ($keyName !== null) unset($this->env->currentProperty);

        if (count($values) == 0) return false;

        $value = lessc::compressList($values, ', ');
        return true;
    }

    protected function parenValue(&$out) {
        $s = $this->seek();

        // speed shortcut
        if (isset($this->buffer[$this->count]) && $this->buffer[$this->count] != "(") {
            return false;
        }

        $inParens = $this->inParens;
        if ($this->literal("(") &&
            ($this->inParens = true) && $this->expression($exp) &&
            $this->literal(")"))
        {
            $out = $exp;
            $this->inParens = $inParens;
            return true;
        } else {
            $this->inParens = $inParens;
            $this->seek($s);
        }

        return false;
    }

    // a single value
    protected function value(&$value) {
        $s = $this->seek();

        // speed shortcut
        if (isset($this->buffer[$this->count]) && $this->buffer[$this->count] == "-") {
            // negation
            if ($this->literal("-", false) &&
                (($this->variable($inner) && $inner = array("variable", $inner)) ||
                    $this->unit($inner) ||
                    $this->parenValue($inner)))
            {
                $value = array("unary", "-", $inner);
                return true;
            } else {
                $this->seek($s);
            }
        }

        if ($this->parenValue($value)) return true;
        if ($this->unit($value)) return true;
        if ($this->color($value)) return true;
        if ($this->func($value)) return true;
        if ($this->stringValue($value)) return true;

        if ($this->keyword($word)) {
            $value = array('keyword', $word);
            return true;
        }

        // try a variable
        if ($this->variable($var)) {
            $value = array('variable', $var);
            return true;
        }

        // unquote string (should this work on any type?
        if ($this->literal("~") && $this->stringValue($str)) {
            $value = array("escape", $str);
            return true;
        } else {
            $this->seek($s);
        }

        // css hack: \0
        if ($this->literal('\\') && $this->match('([0-9]+)', $m)) {
            $value = array('keyword', '\\'.$m[1]);
            return true;
        } else {
            $this->seek($s);
        }

        return false;
    }

    // an import statement
    protected function import(&$out) {
        if (!$this->literal('@import')) return false;

        // @import "something.css" media;
        // @import url("something.css") media;
        // @import url(something.css) media;

        if ($this->propertyValue($value)) {
            $out = array("import", $value);
            return true;
        }
    }

    protected function mediaQueryList(&$out) {
        if ($this->genericList($list, "mediaQuery", ",", false)) {
            $out = $list[2];
            return true;
        }
        return false;
    }

    protected function mediaQuery(&$out) {
        $s = $this->seek();

        $expressions = null;
        $parts = array();

        if (($this->literal("only") && ($only = true) || $this->literal("not") && ($not = true) || true) && $this->keyword($mediaType)) {
            $prop = array("mediaType");
            if (isset($only)) $prop[] = "only";
            if (isset($not)) $prop[] = "not";
            $prop[] = $mediaType;
            $parts[] = $prop;
        } else {
            $this->seek($s);
        }


        if (!empty($mediaType) && !$this->literal("and")) {
            // ~
        } else {
            $this->genericList($expressions, "mediaExpression", "and", false);
            if (is_array($expressions)) $parts = array_merge($parts, $expressions[2]);
        }

        if (count($parts) == 0) {
            $this->seek($s);
            return false;
        }

        $out = $parts;
        return true;
    }

    protected function mediaExpression(&$out) {
        $s = $this->seek();
        $value = null;
        if ($this->literal("(") &&
            $this->keyword($feature) &&
            ($this->literal(":") && $this->expression($value) || true) &&
            $this->literal(")"))
        {
            $out = array("mediaExp", $feature);
            if ($value) $out[] = $value;
            return true;
        } elseif ($this->variable($variable)) {
            $out = array('variable', $variable);
            return true;
        }

        $this->seek($s);
        return false;
    }

    // an unbounded string stopped by $end
    protected function openString($end, &$out, $nestingOpen=null, $rejectStrs = null) {
        $oldWhite = $this->eatWhiteDefault;
        $this->eatWhiteDefault = false;

        $stop = array("'", '"', "@{", $end);
        $stop = array_map(array("lessc", "preg_quote"), $stop);
        // $stop[] = self::$commentMulti;

        if (!is_null($rejectStrs)) {
            $stop = array_merge($stop, $rejectStrs);
        }

        $patt = '(.*?)('.implode("|", $stop).')';

        $nestingLevel = 0;

        $content = array();
        while ($this->match($patt, $m, false)) {
            if (!empty($m[1])) {
                $content[] = $m[1];
                if ($nestingOpen) {
                    $nestingLevel += substr_count($m[1], $nestingOpen);
                }
            }

            $tok = $m[2];

            $this->count-= strlen($tok);
            if ($tok == $end) {
                if ($nestingLevel == 0) {
                    break;
                } else {
                    $nestingLevel--;
                }
            }

            if (($tok == "'" || $tok == '"') && $this->stringValue($str)) {
                $content[] = $str;
                continue;
            }

            if ($tok == "@{" && $this->interpolation($inter)) {
                $content[] = $inter;
                continue;
            }

            if (!empty($rejectStrs) && in_array($tok, $rejectStrs)) {
                break;
            }

            $content[] = $tok;
            $this->count+= strlen($tok);
        }

        $this->eatWhiteDefault = $oldWhite;

        if (count($content) == 0) return false;

        // trim the end
        if (is_string(end($content))) {
            $content[count($content) - 1] = rtrim(end($content));
        }

        $out = array("string", "", $content);
        return true;
    }

    protected function stringValue(&$out) {
        $s = $this->seek();
        if ($this->literal('"', false)) {
            $delim = '"';
        } elseif ($this->literal("'", false)) {
            $delim = "'";
        } else {
            return false;
        }

        $content = array();

        // look for either ending delim , escape, or string interpolation
        $patt = '([^\n]*?)(@\{|\\\\|' .
            lessc::preg_quote($delim).')';

        $oldWhite = $this->eatWhiteDefault;
        $this->eatWhiteDefault = false;

        while ($this->match($patt, $m, false)) {
            $content[] = $m[1];
            if ($m[2] == "@{") {
                $this->count -= strlen($m[2]);
                if ($this->interpolation($inter, false)) {
                    $content[] = $inter;
                } else {
                    $this->count += strlen($m[2]);
                    $content[] = "@{"; // ignore it
                }
            } elseif ($m[2] == '\\') {
                $content[] = $m[2];
                if ($this->literal($delim, false)) {
                    $content[] = $delim;
                }
            } else {
                $this->count -= strlen($delim);
                break; // delim
            }
        }

        $this->eatWhiteDefault = $oldWhite;

        if ($this->literal($delim)) {
            $out = array("string", $delim, $content);
            return true;
        }

        $this->seek($s);
        return false;
    }

    protected function interpolation(&$out) {
        $oldWhite = $this->eatWhiteDefault;
        $this->eatWhiteDefault = true;

        $s = $this->seek();
        if ($this->literal("@{") &&
            $this->openString("}", $interp, null, array("'", '"', ";")) &&
            $this->literal("}", false))
        {
            $out = array("interpolate", $interp);
            $this->eatWhiteDefault = $oldWhite;
            if ($this->eatWhiteDefault) $this->whitespace();
            return true;
        }

        $this->eatWhiteDefault = $oldWhite;
        $this->seek($s);
        return false;
    }

    protected function unit(&$unit) {
        // speed shortcut
        if (isset($this->buffer[$this->count])) {
            $char = $this->buffer[$this->count];
            if (!ctype_digit($char) && $char != ".") return false;
        }

        if ($this->match('([0-9]+(?:\.[0-9]*)?|\.[0-9]+)([%a-zA-Z]+)?', $m)) {
            $unit = array("number", $m[1], empty($m[2]) ? "" : $m[2]);
            return true;
        }
        return false;
    }

    // a # color
    protected function color(&$out) {
        if ($this->match('(#(?:[0-9a-f]{8}|[0-9a-f]{6}|[0-9a-f]{3}))', $m)) {
            if (strlen($m[1]) > 7) {
                $out = array("string", "", array($m[1]));
            } else {
                $out = array("raw_color", $m[1]);
            }
            return true;
        }

        return false;
    }

    // consume an argument definition list surrounded by ()
    // each argument is a variable name with optional value
    // or at the end a ... or a variable named followed by ...
    // arguments are separated by , unless a ; is in the list, then ; is the
    // delimiter.
    protected function argumentDef(&$args, &$isVararg) {
        $s = $this->seek();
        if (!$this->literal('(')) return false;

        $values = array();
        $delim = ",";
        $method = "expressionList";

        $isVararg = false;
        while (true) {
            if ($this->literal("...")) {
                $isVararg = true;
                break;
            }

            if ($this->$method($value)) {
                if ($value[0] == "variable") {
                    $arg = array("arg", $value[1]);
                    $ss = $this->seek();

                    if ($this->assign() && $this->$method($rhs)) {
                        $arg[] = $rhs;
                    } else {
                        $this->seek($ss);
                        if ($this->literal("...")) {
                            $arg[0] = "rest";
                            $isVararg = true;
                        }
                    }

                    $values[] = $arg;
                    if ($isVararg) break;
                    continue;
                } else {
                    $values[] = array("lit", $value);
                }
            }


            if (!$this->literal($delim)) {
                if ($delim == "," && $this->literal(";")) {
                    // found new delim, convert existing args
                    $delim = ";";
                    $method = "propertyValue";

                    // transform arg list
                    if (isset($values[1])) { // 2 items
                        $newList = array();
                        foreach ($values as $i => $arg) {
                            switch($arg[0]) {
                                case "arg":
                                    if ($i) {
                                        $this->throwError("Cannot mix ; and , as delimiter types");
                                    }
                                    $newList[] = $arg[2];
                                    break;
                                case "lit":
                                    $newList[] = $arg[1];
                                    break;
                                case "rest":
                                    $this->throwError("Unexpected rest before semicolon");
                            }
                        }

                        $newList = array("list", ", ", $newList);

                        switch ($values[0][0]) {
                            case "arg":
                                $newArg = array("arg", $values[0][1], $newList);
                                break;
                            case "lit":
                                $newArg = array("lit", $newList);
                                break;
                        }

                    } elseif ($values) { // 1 item
                        $newArg = $values[0];
                    }

                    if ($newArg) {
                        $values = array($newArg);
                    }
                } else {
                    break;
                }
            }
        }

        if (!$this->literal(')')) {
            $this->seek($s);
            return false;
        }

        $args = $values;

        return true;
    }

    // consume a list of tags
    // this accepts a hanging delimiter
    protected function tags(&$tags, $simple = false, $delim = ',') {
        $tags = array();
        while ($this->tag($tt, $simple)) {
            $tags[] = $tt;
            if (!$this->literal($delim)) break;
        }
        if (count($tags) == 0) return false;

        return true;
    }

    // list of tags of specifying mixin path
    // optionally separated by > (lazy, accepts extra >)
    protected function mixinTags(&$tags) {
        $tags = array();
        while ($this->tag($tt, true)) {
            $tags[] = $tt;
            $this->literal(">");
        }

        if (count($tags) == 0) return false;

        return true;
    }

    // a bracketed value (contained within in a tag definition)
    protected function tagBracket(&$parts, &$hasExpression) {
        // speed shortcut
        if (isset($this->buffer[$this->count]) && $this->buffer[$this->count] != "[") {
            return false;
        }

        $s = $this->seek();

        $hasInterpolation = false;

        if ($this->literal("[", false)) {
            $attrParts = array("[");
            // keyword, string, operator
            while (true) {
                if ($this->literal("]", false)) {
                    $this->count--;
                    break; // get out early
                }

                if ($this->match('\s+', $m)) {
                    $attrParts[] = " ";
                    continue;
                }
                if ($this->stringValue($str)) {
                    // escape parent selector, (yuck)
                    foreach ($str[2] as &$chunk) {
                        if (is_string($chunk)) {
                            $chunk = str_replace($this->lessc->parentSelector, "$&$", $chunk);
                        }
                    }

                    $attrParts[] = $str;
                    $hasInterpolation = true;
                    continue;
                }

                if ($this->keyword($word)) {
                    $attrParts[] = $word;
                    continue;
                }

                if ($this->interpolation($inter, false)) {
                    $attrParts[] = $inter;
                    $hasInterpolation = true;
                    continue;
                }

                // operator, handles attr namespace too
                if ($this->match('[|-~\$\*\^=]+', $m)) {
                    $attrParts[] = $m[0];
                    continue;
                }

                break;
            }

            if ($this->literal("]", false)) {
                $attrParts[] = "]";
                foreach ($attrParts as $part) {
                    $parts[] = $part;
                }
                $hasExpression = $hasExpression || $hasInterpolation;
                return true;
            }
            $this->seek($s);
        }

        $this->seek($s);
        return false;
    }

    // a space separated list of selectors
    protected function tag(&$tag, $simple = false) {
        if ($simple)
            $chars = '^@,:;{}\][>\(\) "\'';
        else
            $chars = '^@,;{}["\'';

        $s = $this->seek();

        $hasExpression = false;
        $parts = array();
        while ($this->tagBracket($parts, $hasExpression));

        $oldWhite = $this->eatWhiteDefault;
        $this->eatWhiteDefault = false;

        while (true) {
            if ($this->match('(['.$chars.'0-9]['.$chars.']*)', $m)) {
                $parts[] = $m[1];
                if ($simple) break;

                while ($this->tagBracket($parts, $hasExpression));
                continue;
            }

            if (isset($this->buffer[$this->count]) && $this->buffer[$this->count] == "@") {
                if ($this->interpolation($interp)) {
                    $hasExpression = true;
                    $interp[2] = true; // don't unescape
                    $parts[] = $interp;
                    continue;
                }

                if ($this->literal("@")) {
                    $parts[] = "@";
                    continue;
                }
            }

            if ($this->unit($unit)) { // for keyframes
                $parts[] = $unit[1];
                $parts[] = $unit[2];
                continue;
            }

            break;
        }

        $this->eatWhiteDefault = $oldWhite;
        if (!$parts) {
            $this->seek($s);
            return false;
        }

        if ($hasExpression) {
            $tag = array("exp", array("string", "", $parts));
        } else {
            $tag = trim(implode($parts));
        }

        $this->whitespace();
        return true;
    }

    // a css function
    protected function func(&$func) {
        $s = $this->seek();

        if ($this->match('(%|[\w\-_][\w\-_:\.]+|[\w_])', $m) && $this->literal('(')) {
            $fname = $m[1];

            $sPreArgs = $this->seek();

            $args = array();
            while (true) {
                $ss = $this->seek();
                // this ugly nonsense is for ie filter properties
                if ($this->keyword($name) && $this->literal('=') && $this->expressionList($value)) {
                    $args[] = array("string", "", array($name, "=", $value));
                } else {
                    $this->seek($ss);
                    if ($this->expressionList($value)) {
                        $args[] = $value;
                    }
                }

                if (!$this->literal(',')) break;
            }
            $args = array('list', ',', $args);

            if ($this->literal(')')) {
                $func = array('function', $fname, $args);
                return true;
            } elseif ($fname == 'url') {
                // couldn't parse and in url? treat as string
                $this->seek($sPreArgs);
                if ($this->openString(")", $string) && $this->literal(")")) {
                    $func = array('function', $fname, $string);
                    return true;
                }
            }
        }

        $this->seek($s);
        return false;
    }

    // consume a less variable
    protected function variable(&$name) {
        $s = $this->seek();
        if ($this->literal($this->lessc->vPrefix, false) &&
            ($this->variable($sub) || $this->keyword($name)))
        {
            if (!empty($sub)) {
                $name = array('variable', $sub);
            } else {
                $name = $this->lessc->vPrefix.$name;
            }
            return true;
        }

        $name = null;
        $this->seek($s);
        return false;
    }

    /**
     * Consume an assignment operator
     * Can optionally take a name that will be set to the current property name
     */
    protected function assign($name = null) {
        if ($name) $this->currentProperty = $name;
        return $this->literal(':') || $this->literal('=');
    }

    // consume a keyword
    protected function keyword(&$word) {
        if ($this->match('([\w_\-\*!"][\w\-_"]*)', $m)) {
            $word = $m[1];
            return true;
        }
        return false;
    }

    // consume an end of statement delimiter
    protected function end() {
        if ($this->literal(';', false)) {
            return true;
        } elseif ($this->count == strlen($this->buffer) || $this->buffer[$this->count] == '}') {
            // if there is end of file or a closing block next then we don't need a ;
            return true;
        }
        return false;
    }

    protected function guards(&$guards) {
        $s = $this->seek();

        if (!$this->literal("when")) {
            $this->seek($s);
            return false;
        }

        $guards = array();

        while ($this->guardGroup($g)) {
            $guards[] = $g;
            if (!$this->literal(",")) break;
        }

        if (count($guards) == 0) {
            $guards = null;
            $this->seek($s);
            return false;
        }

        return true;
    }

    // a bunch of guards that are and'd together
    // TODO rename to guardGroup
    protected function guardGroup(&$guardGroup) {
        $s = $this->seek();
        $guardGroup = array();
        while ($this->guard($guard)) {
            $guardGroup[] = $guard;
            if (!$this->literal("and")) break;
        }

        if (count($guardGroup) == 0) {
            $guardGroup = null;
            $this->seek($s);
            return false;
        }

        return true;
    }

    protected function guard(&$guard) {
        $s = $this->seek();
        $negate = $this->literal("not");

        if ($this->literal("(") && $this->expression($exp) && $this->literal(")")) {
            $guard = $exp;
            if ($negate) $guard = array("negate", $guard);
            return true;
        }

        $this->seek($s);
        return false;
    }

    /* raw parsing functions */

    protected function literal($what, $eatWhitespace = null) {
        if ($eatWhitespace === null) $eatWhitespace = $this->eatWhiteDefault;

        // shortcut on single letter
        if (!isset($what[1]) && isset($this->buffer[$this->count])) {
            if ($this->buffer[$this->count] == $what) {
                if (!$eatWhitespace) {
                    $this->count++;
                    return true;
                }
                // goes below...
            } else {
                return false;
            }
        }

        if (!isset(self::$literalCache[$what])) {
            self::$literalCache[$what] = lessc::preg_quote($what);
        }

        return $this->match(self::$literalCache[$what], $m, $eatWhitespace);
    }

    protected function genericList(&$out, $parseItem, $delim="", $flatten=true) {
        $s = $this->seek();
        $items = array();
        while ($this->$parseItem($value)) {
            $items[] = $value;
            if ($delim) {
                if (!$this->literal($delim)) break;
            }
        }

        if (count($items) == 0) {
            $this->seek($s);
            return false;
        }

        if ($flatten && count($items) == 1) {
            $out = $items[0];
        } else {
            $out = array("list", $delim, $items);
        }

        return true;
    }


    // advance counter to next occurrence of $what
    // $until - don't include $what in advance
    // $allowNewline, if string, will be used as valid char set
    protected function to($what, &$out, $until = false, $allowNewline = false) {
        if (is_string($allowNewline)) {
            $validChars = $allowNewline;
        } else {
            $validChars = $allowNewline ? "." : "[^\n]";
        }
        if (!$this->match('('.$validChars.'*?)'.lessc::preg_quote($what), $m, !$until)) return false;
        if ($until) $this->count -= strlen($what); // give back $what
        $out = $m[1];
        return true;
    }

    // try to match something on head of buffer
    protected function match($regex, &$out, $eatWhitespace = null) {
        if ($eatWhitespace === null) $eatWhitespace = $this->eatWhiteDefault;

        $r = '/'.$regex.($eatWhitespace && !$this->writeComments ? '\s*' : '').'/Ais';
        if (preg_match($r, $this->buffer, $out, 0, $this->count)) {
            $this->count += strlen($out[0]);
            if ($eatWhitespace && $this->writeComments) $this->whitespace();
            return true;
        }
        return false;
    }

    // match some whitespace
    protected function whitespace() {
        if ($this->writeComments) {
            $gotWhite = false;
            while (preg_match(self::$whitePattern, $this->buffer, $m, 0, $this->count)) {
                if (isset($m[1]) && empty($this->seenComments[$this->count])) {
                    $this->append(array("comment", $m[1]));
                    $this->seenComments[$this->count] = true;
                }
                $this->count += strlen($m[0]);
                $gotWhite = true;
            }
            return $gotWhite;
        } else {
            $this->match("", $m);
            return strlen($m[0]) > 0;
        }
    }

    // match something without consuming it
    protected function peek($regex, &$out = null, $from=null) {
        if (is_null($from)) $from = $this->count;
        $r = '/'.$regex.'/Ais';
        $result = preg_match($r, $this->buffer, $out, 0, $from);

        return $result;
    }

    // seek to a spot in the buffer or return where we are on no argument
    protected function seek($where = null) {
        if ($where === null) return $this->count;
        else $this->count = $where;
        return true;
    }

    /* misc functions */

    public function throwError($msg = "parse error", $count = null) {
        $count = is_null($count) ? $this->count : $count;

        $line = $this->line +
            substr_count(substr($this->buffer, 0, $count), "\n");

        if (!empty($this->sourceName)) {
            $loc = "$this->sourceName on line $line";
        } else {
            $loc = "line: $line";
        }

        // TODO this depends on $this->count
        if ($this->peek("(.*?)(\n|$)", $m, $count)) {
            throw new \Exception("$msg: failed at `$m[1]` $loc");
        } else {
            throw new \Exception("$msg: $loc");
        }
    }

    protected function pushBlock($selectors=null, $type=null) {
        $b = new \stdClass();
        $b->parent = $this->env;

        $b->type = $type;
        $b->id = self::$nextBlockId++;

        $b->isVararg = false; // TODO: kill me from here
        $b->tags = $selectors;

        $b->props = array();
        $b->children = array();

        // add a reference to the parser so
        // we can access the parser to throw errors
        // or retrieve the sourceName of this block.
        $b->parser = $this;

        // so we know the position of this block
        $b->count = $this->count;

        $this->env = $b;
        return $b;
    }

    // push a block that doesn't multiply tags
    protected function pushSpecialBlock($type) {
        return $this->pushBlock(null, $type);
    }

    // append a property to the current block
    protected function append($prop, $pos = null) {
        if ($pos !== null) $prop[-1] = $pos;
        $this->env->props[] = $prop;
    }

    // pop something off the stack
    protected function pop() {
        $old = $this->env;
        $this->env = $this->env->parent;
        return $old;
    }

    // remove comments from $text
    // todo: make it work for all functions, not just url
    protected function removeComments($text) {
        $look = array(
            'url(', '//', '/*', '"', "'"
        );

        $out = '';
        $min = null;
        while (true) {
            // find the next item
            foreach ($look as $token) {
                $pos = strpos($text, $token);
                if ($pos !== false) {
                    if (!isset($min) || $pos < $min[1]) $min = array($token, $pos);
                }
            }

            if (is_null($min)) break;

            $count = $min[1];
            $skip = 0;
            $newlines = 0;
            switch ($min[0]) {
                case 'url(':
                    if (preg_match('/url\(.*?\)/', $text, $m, 0, $count))
                        $count += strlen($m[0]) - strlen($min[0]);
                    break;
                case '"':
                case "'":
                    if (preg_match('/'.$min[0].'.*?(?<!\\\\)'.$min[0].'/', $text, $m, 0, $count))
                        $count += strlen($m[0]) - 1;
                    break;
                case '//':
                    $skip = strpos($text, "\n", $count);
                    if ($skip === false) $skip = strlen($text) - $count;
                    else $skip -= $count;
                    break;
                case '/*':
                    if (preg_match('/\/\*.*?\*\//s', $text, $m, 0, $count)) {
                        $skip = strlen($m[0]);
                        $newlines = substr_count($m[0], "\n");
                    }
                    break;
            }

            if ($skip == 0) $count += strlen($min[0]);

            $out .= substr($text, 0, $count).str_repeat("\n", $newlines);
            $text = substr($text, $count + $skip);

            $min = null;
        }

        return $out.$text;
    }

}

class lessc_formatter_classic {
    public $indentChar = "  ";

    public $break = "\n";
    public $open = " {";
    public $close = "}";
    public $selectorSeparator = ", ";
    public $assignSeparator = ":";

    public $openSingle = " { ";
    public $closeSingle = " }";

    public $disableSingle = false;
    public $breakSelectors = false;

    public $compressColors = false;

    public function __construct() {
        $this->indentLevel = 0;
    }

    public function indentStr($n = 0) {
        return str_repeat($this->indentChar, max($this->indentLevel + $n, 0));
    }

    public function property($name, $value) {
        return $name . $this->assignSeparator . $value . ";";
    }

    protected function isEmpty($block) {
        if (empty($block->lines)) {
            foreach ($block->children as $child) {
                if (!$this->isEmpty($child)) return false;
            }

            return true;
        }
        return false;
    }

    public function block($block) {
        if ($this->isEmpty($block)) return;

        $inner = $pre = $this->indentStr();

        $isSingle = !$this->disableSingle &&
            is_null($block->type) && count($block->lines) == 1;

        if (!empty($block->selectors)) {
            $this->indentLevel++;

            if ($this->breakSelectors) {
                $selectorSeparator = $this->selectorSeparator . $this->break . $pre;
            } else {
                $selectorSeparator = $this->selectorSeparator;
            }

            echo $pre .
                implode($selectorSeparator, $block->selectors);
            if ($isSingle) {
                echo $this->openSingle;
                $inner = "";
            } else {
                echo $this->open . $this->break;
                $inner = $this->indentStr();
            }

        }

        if (!empty($block->lines)) {
            $glue = $this->break.$inner;
            echo $inner . implode($glue, $block->lines);
            if (!$isSingle && !empty($block->children)) {
                echo $this->break;
            }
        }

        foreach ($block->children as $child) {
            $this->block($child);
        }

        if (!empty($block->selectors)) {
            if (!$isSingle && empty($block->children)) echo $this->break;

            if ($isSingle) {
                echo $this->closeSingle . $this->break;
            } else {
                echo $pre . $this->close . $this->break;
            }

            $this->indentLevel--;
        }
    }
}

class lessc_formatter_compressed extends lessc_formatter_classic {
    public $disableSingle = true;
    public $open = "{";
    public $selectorSeparator = ",";
    public $assignSeparator = ":";
    public $break = "";
    public $compressColors = true;

    public function indentStr($n = 0) {
        return "";
    }
}

class lessc_formatter_lessjs extends lessc_formatter_classic {
    public $disableSingle = true;
    public $breakSelectors = true;
    public $assignSeparator = ": ";
    public $selectorSeparator = ",";
    public $indentLevel;
}