<?php
/* SVN FILE: $Id$ */
/**
 * SassScriptParser 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 'SassScriptLexer.php';
require_once 'SassScriptParserExceptions.php';

/**
 * SassScriptParser class.
 * Parses SassScript. SassScript is lexed into {@link http://en.wikipedia.org/wiki/Reverse_Polish_notation Reverse Polish notation} by the SassScriptLexer and
 *  the calculated result returned.
 * @package      PHamlP
 * @subpackage  Sass.script
 */
class SassScriptParser
{
  const MATCH_INTERPOLATION = '/(?<!\\\\)#\{(.*?)\}/';
  const DEFAULT_ENV = 0;
  const CSS_RULE = 1;
  const CSS_PROPERTY = 2;

  /**
   * @var SassContext Used for error reporting
   */
  public static $context;

  /**
   * @var SassScriptLexer the lexer object
   */
  public $lexer;

  /**
   * Hold a copy of a parser available to the general public.
   */
  public static $instance;

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

  /**
   * Replace interpolated SassScript contained in '#{}' with the parsed value.
   * @param string $string the text to interpolate
   * @param SassContext $context the context in which the string is interpolated
   * @return string the interpolated text
   */
  public function interpolate($string, $context)
  {
    for ($i = 0, $n = preg_match_all(self::MATCH_INTERPOLATION, $string, $matches); $i < $n; $i++) {
      $var = $this->evaluate($matches[1][$i], $context);

      if ($var instanceOf SassString) {
        $var = $var->value;
      } else {
        $var = $var->toString();
      }

      if (preg_match('/^unquote\((["\'])(.*)\1\)$/', $var, $match)) {
          $val = $match[2];
      } elseif ($var == '""') {
          $val = "";
      } elseif (preg_match('/^(["\'])(.*)\1$/', $var, $match)) {
          $val = $match[2];
      } else {
          $val = $var;
      }
      $matches[1][$i] = $val;
    }

    return str_replace($matches[0], $matches[1], $string);
  }

  /**
   * Evaluate a SassScript.
   * @param string $expression expression to parse
   * @param SassContext $context the context in which the expression is evaluated
   * @param  integer $environment the environment in which the expression is evaluated
   * @return SassLiteral parsed value
   */
  public function evaluate($expression, $context, $environment = self::DEFAULT_ENV)
  {
    self::$context = $context;
    $operands = array();

    $tokens = $this->parse($expression, $context, $environment);

    while (count($tokens)) {
      $token = array_shift($tokens);
      if ($token instanceof SassScriptFunction) {
        $perform = $token->perform();
        array_push($operands, $perform);
      } elseif ($token instanceof SassLiteral) {
        if ($token instanceof SassString) {
          $token = new SassString($this->interpolate($token->toString(), self::$context));
        }
        array_push($operands, $token);
      } else {
        $args = array();
        for ($i = 0, $c = $token->operandCount; $i < $c; $i++) {
          $args[] = array_pop($operands);
        }
        array_push($operands, $token->perform($args));
      }
    }

    return self::makeSingular($operands);
  }

  /**
   * Parse SassScript to a set of tokens in RPN
   * using the Shunting Yard Algorithm.
   * @param string $expression expression to parse
   * @param SassContext $context the context in which the expression is parsed
   * @param  integer $environment the environment in which the expression is parsed
   * @return array tokens in RPN
   */
  public function parse($expression, $context, $environment=self::DEFAULT_ENV)
  {
    $outputQueue = array();
    $operatorStack = array();
    $parenthesis = 0;

    $tokens = $this->lexer->lex($expression, $context);

    foreach ($tokens as $i=>$token) {
      // If two literals/expessions are seperated by whitespace use the concat operator
      if (empty($token)) {
        if (isset($tokens[$i+1])) {
          if ($i > 0 && (!$tokens[$i-1] instanceof SassScriptOperation || $tokens[$i-1]->operator === SassScriptOperation::$operators[')'][0]) &&
              (!$tokens[$i+1] instanceof SassScriptOperation || $tokens[$i+1]->operator === SassScriptOperation::$operators['('][0])) {
            $token = new SassScriptOperation(SassScriptOperation::$defaultOperator, $context);
          } else {
            continue;
          }
        }
      } elseif ($token instanceof SassScriptVariable) {
        $token = $token->evaluate($context);
        $environment = self::DEFAULT_ENV;
      }

      // If the token is a number or function add it to the output queue.
       if ($token instanceof SassLiteral || $token instanceof SassScriptFunction) {
         if ($environment === self::CSS_PROPERTY && $token instanceof SassNumber && !$parenthesis) {
          $token->inExpression = false;
         }
        array_push($outputQueue, $token);
      }
      // If the token is an operation
      elseif ($token instanceof SassScriptOperation) {
        // If the token is a left parenthesis push it onto the stack.
        if ($token->operator == SassScriptOperation::$operators['('][0]) {
          array_push($operatorStack, $token);
          $parenthesis++;
        }
        // If the token is a right parenthesis:
        elseif ($token->operator == SassScriptOperation::$operators[')'][0]) {
          $parenthesis--;
          while ($c = count($operatorStack)) {
            // If the token at the top of the stack is a left parenthesis
            if ($operatorStack[$c - 1]->operator == SassScriptOperation::$operators['('][0]) {
              // Pop the left parenthesis from the stack, but not onto the output queue.
              array_pop($operatorStack);
              break;
            }
            // else pop the operator off the stack onto the output queue.
            array_push($outputQueue, array_pop($operatorStack));
          }
          // If the stack runs out without finding a left parenthesis
          // there are mismatched parentheses.
          if ($c <= 0) {
            array_push($outputQueue, new SassString(')'));
            break;
          }
        }
        // the token is an operator, o1, so:
        else {
          // while there is an operator, o2, at the top of the stack
          while ($c = count($operatorStack)) {
            $operation = $operatorStack[$c - 1];
            // if o2 is left parenthesis, or
            // the o1 has left associativty and greater precedence than o2, or
            // the o1 has right associativity and lower or equal precedence than o2
            if (($operation->operator == SassScriptOperation::$operators['('][0]) ||
              ($token->associativity == 'l' && $token->precedence > $operation->precedence) ||
              ($token->associativity == 'r' && $token->precedence <= $operation->precedence)) {
              break; // stop checking operators
            }
            //pop o2 off the stack and onto the output queue
            array_push($outputQueue, array_pop($operatorStack));
          }
          // push o1 onto the stack
          array_push($operatorStack, $token);
        }
      }
    }

    // When there are no more tokens
    while ($c = count($operatorStack)) { // While there are operators on the stack:
      if ($operatorStack[$c - 1]->operator !== SassScriptOperation::$operators['('][0]) {
        array_push($outputQueue, array_pop($operatorStack));
      } else {
        throw new SassScriptParserException('Unmatched parentheses', $context->node);
      }
    }

    return $outputQueue;
  }

  /**
   * Reduces a set down to a singular form
   */
  public static function makeSingular($operands)
  {
    if (count($operands) == 1) {
      return $operands[0];
    }

    $result = null;
    foreach ($operands as $i => $operand) {
      if (is_object($operand)) {
        if (!$result) {
          $result = $operand;
          continue;
        }
        if ($result instanceOf SassString) {
          $result = $result->op_concat($operand);
        } else {
          $result = $result->op_plus($operand);
        }
      } else {
        $string = new SassString(' ');
        if (!$result) {
          $result = $string;
        } else {
          $result = $result->op_plus($string);
        }
      }
    }

    return $result ? $result : array_shift($operands);
  }
}
