<?php
/**
* Scans a string and creates list of tokens.
*
* @license http://www.opensource.org/licenses/mit-license.php The MIT License
* @copyright Copyright 2010-2014 PhpCss Team
*/
namespace PhpCss {

  use UnexpectedValueException;

  /**
  * Scans a string and creates list of tokens.
  *
  * The actual result depends on the status, the status
  * class does the actual token matching and generation, the scanner handles, to loops and
  * delegations.
  */
  class Scanner {

    /**
    * Scanner status object
    * @var Scanner\Status
    */
    private $_status;
    /**
    * string to parse
    * @var string
    */
    private $_buffer = '';
    /**
    * current offset
    * @var integer
    */
    private $_offset = 0;

    /**
    * Constructor, set status object
    *
    * @param Scanner\Status $status
    */
    public function __construct(Scanner\Status $status) {
      $this->_status = $status;
    }

    /**
     * Scan a string for tokens
     *
     * @param array &$target token target
     * @param string $string content string
     * @param integer $offset start offset
     * @throws UnexpectedValueException
     * @return integer new offset
     */
    public function scan(array &$target, string $string, int $offset = 0): int {
      $this->_buffer = $string;
      $this->_offset = $offset;
      while ($token = $this->_next()) {
        $target[] = $token;
        // switch back to previous scanner
        if ($this->_status->isEndToken($token)) {
          return $this->_offset;
        }
        // check for status switch
        if ($newStatus = $this->_status->getNewStatus($token)) {
          // delegate to subscanner
          $this->_offset = $this->_delegate($target, $newStatus);
        }
      }
      if ($this->_offset < strlen($this->_buffer)) {
        /**
        * @todo a some substring logic for large strings
        */
        throw new Exception\InvalidCharacterException(
          $this->_buffer,
          $this->_offset,
          $this->_status
        );
      }
      return $this->_offset;
    }

    /**
    * Get next token
    *
    * @return Scanner\Token|NULL
    */
    private function _next(): ?Scanner\Token {
      if (($token = $this->_status->getToken($this->_buffer, $this->_offset)) &&
          $token->length > 0) {
        $this->_offset += $token->length;
        return $token;
      }
      return NULL;
    }

    /**
    * Got new status, delegate to subscanner.
    *
    * If the status returns a new status object, a new scanner is created to handle it.
    *
    * @param Scanner\Token[] $target
    * @param Scanner\Status $status
    * @return int
    */
    private function _delegate(array &$target, Scanner\Status $status): int {
      $scanner = new self($status);
      return $scanner->scan($target, $this->_buffer, $this->_offset);
    }

    public function getStatus(): Scanner\Status {
      return $this->_status;
    }
  }
}