<?php
/* SVN FILE: $Id$ */
/**
 * SassScriptLexer class file.
 * @author      Chris Yates <chris.l.yates@gmail.com>
 * @copyright   Copyright (c) 2010 PBM Web Development
 * @license      http://phamlp.googlecode.com/files/license.txt
 * @package      PHamlP
 * @subpackage  Sass.script
 */

require_once('literals/SassBoolean.php');
require_once('literals/SassColour.php');
require_once('literals/SassNumber.php');
require_once('literals/SassString.php');
require_once('literals/SassList.php');
require_once('SassScriptFunction.php');
require_once('SassScriptOperation.php');
require_once('SassScriptVariable.php');

/**
 * SassScriptLexer class.
 * Lexes SassSCript into tokens for the parser.
 *
 * Implements a {@link http://en.wikipedia.org/wiki/Shunting-yard_algorithm Shunting-yard algorithm} to provide {@link http://en.wikipedia.org/wiki/Reverse_Polish_notation Reverse Polish notation} output.
 * @package      PHamlP
 * @subpackage  Sass.script
 */
class SassScriptLexer {
  const MATCH_WHITESPACE = '/^\s+/';

  /**
   * Static holder for last instance of SassScriptLexer
   */
  static public $instance;

  /**
   * @var SassScriptParser the parser object
   */
  public $parser;

  /**
  * SassScriptLexer constructor.
  * @return SassScriptLexer
  */
  public function __construct($parser) {
    $this->parser = $parser;
    self::$instance = $this;
  }

  /**
   * Lex an expression into SassScript tokens.
   * @param string expression to lex
   * @param SassContext the context in which the expression is lexed
   * @return array tokens
   */
  public function lex($string, $context) {
    // if it's already lexed, just return it as-is
    if (is_object($string)) {
      return array($string);
    }
    if (is_array($string)) {
      return $string;
    }
    // whilst the string is not empty, split it into it's tokens.
    while ($string !== false) {
      if (($match = $this->isWhitespace($string)) !== false) {
        $tokens[] = null;
      }
      elseif (($match = SassScriptFunction::isa($string)) !== false) {
        preg_match(SassScriptFunction::MATCH_FUNC, $match, $matches);
        $args = array();
        foreach (SassScriptFunction::extractArgs($matches[SassScriptFunction::ARGS], false, $context) as $key => $expression) {
          $args[$key] = $this->parser->evaluate($expression, $context);
        }
        $tokens[] = new SassScriptFunction($matches[SassScriptFunction::NAME], $args);
      }
      elseif (($match = SassBoolean::isa($string)) !== false) {
        $tokens[] = new SassBoolean($match);
      }
      elseif (($match = SassColour::isa($string)) !== false) {
        $tokens[] = new SassColour($match);
      }
      elseif (($match = SassNumber::isa($string)) !== false) {
        $tokens[] = new SassNumber($match);
      }
      elseif (($match = SassString::isa($string)) !== false) {
        $stringed = new SassString($match);
        if (strlen($stringed->quote) == 0 && SassList::isa($string) !== false) {
          $tokens[] = new SassList($string);
        } else {
          $tokens[] = $stringed;
        }
      }
      elseif (($match = SassScriptOperation::isa($string)) !== false) {
        $tokens[] = new SassScriptOperation($match);
      }
      elseif (($match = SassScriptVariable::isa($string)) !== false) {
        $tokens[] = new SassScriptVariable($match);
      }
      else {
        $_string = $string;
        $match = '';
        while (strlen($_string) && !$this->isWhitespace($_string)) {
          foreach (SassScriptOperation::$inStrOperators as $operator) {
            if (substr($_string, 0, strlen($operator)) == $operator) {
              break 2;
            }
          }
          $match .= $_string[0];
          $_string = substr($_string, 1);
        }
        $tokens[] = new SassString($match);
      }
      $string = substr($string, strlen($match));
    }
    return $tokens;
  }

  /**
   * Returns a value indicating if a token of this type can be matched at
   * the start of the subject string.
   * @param string the subject string
   * @return mixed match at the start of the string or false if no match
   */
  public function isWhitespace($subject) {
    return (preg_match(self::MATCH_WHITESPACE, $subject, $matches) ? $matches[0] : false);
  }
}
