<?php
/* SVN FILE: $Id: SassScriptOperation.php 118 2010-09-21 09:45:11Z chris.l.yates@gmail.com $ */
/**
 * SassScriptOperation 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
 */

/**
 * SassScriptOperation class.
 * The operation to perform.
 * @package			PHamlP
 * @subpackage	Sass.script
 */
class SassScriptOperation {
  const MATCH = '/^(\(|\)|\+|-|\*|\/|%|<=|>=|<|>|==|!=|=|#{|}|,|and\b|or\b|xor\b|not\b)/';

	/**
	 * @var array map symbols to tokens.
	 * A token is function, associativity, precedence, number of operands
	 */
	public static $operators = array(
		'*'		=> array('times',		'l', 8, 2),
		'/'		=> array('div',			'l', 8, 2),
		'%'		=> array('modulo',	'l', 8, 2),
		'+'		=> array('plus',		'l', 7, 2),
		'-'		=> array('minus',		'l', 7, 2),
		'<<'	=> array('shiftl',	'l', 6, 2),
		'>>'	=> array('shiftr',	'l', 6, 2),
		'<='	=> array('lte',			'l', 5, 2),
		'>='	=> array('gte',			'l', 5, 2),
		'<'		=> array('lt',			'l', 5, 2),
		'>'		=> array('gt',			'l', 5, 2),
		'=='	=> array('eq',			'l', 4, 2),
		'!='	=> array('neq',			'l', 4, 2),
		'and'	=> array('and',			'l', 3, 2),
		'or'	=> array('or',			'l', 3, 2),
		'xor'	=> array('xor',			'l', 3, 2),
		'not'	=> array('not',			'l', 3, 1),
		'='		=> array('assign',	'l', 2, 2),
		')'		=> array('rparen',	'l', 1),
		'('		=> array('lparen',	'l', 0),
		','		=> array('comma',		'l', 0, 2),
		'#{'	=> array('begin_interpolation'),
		'}'		=> array('end_interpolation'),
	);
	
	/**
	 * @var array operators with meaning in uquoted strings;
	 * selectors, property names and values
	 */
	public static $inStrOperators = array(',', '#{');
 
	/**
	 * @var array default operator token.
	 */
	public static $defaultOperator = array('concat', 'l', 0, 2);

	/**
	 * @var string operator for this operation
	 */
	private $operator;
	/**
	 * @var string associativity of the operator; left or right
	 */
	private $associativity;
	/**
	 * @var integer precedence of the operator
	 */
	private $precedence;
	/**
	 * @var integer number of operands required by the operator
	 */
	private $operandCount;

	/**
	 * SassScriptOperation constructor
	 *
	 * @param mixed string: operator symbol; array: operator token
	 * @return SassScriptOperation
	 */
	public function __construct($operation) {
		if (is_string($operation)) {
			$operation = self::$operators[$operation];
		}
		$this->operator			 = $operation[0];
		if (isset($operation[1])) {
			$this->associativity = $operation[1];
			$this->precedence		 = $operation[2];
			$this->operandCount	 = (isset($operation[3]) ?
					$operation[3] : null);
		}
	}

	/**
	 * Getter function for properties
	 * @param string name of property
	 * @return mixed value of the property
	 * @throws SassScriptOperationException if the property does not exist
	 */
	public function __get($name) {
		if (property_exists($this, $name)) {
			return $this->$name;
		}
	  else {
			throw new SassScriptOperationException('Unknown property: {name}', array('{name}'=>$name), SassScriptParser::$context->node);
	  }
	}

	/**
	 * Performs this operation.
	 * @param array operands for the operation. The operands are SassLiterals
	 * @return SassLiteral the result of the operation
	 * @throws SassScriptOperationException if the oprand count is incorrect or
	 * the operation is undefined
	 */
	public function perform($operands) {
		if (count($operands) !== $this->operandCount) {
			throw new SassScriptOperationException('Incorrect operand count for {operation}; expected {expected}, received {received}', array('{operation}'=>get_class($operands[0]), '{expected}'=>$this->operandCount, '{received}'=>count($operands)), SassScriptParser::$context->node);
		}
		
		if (count($operands) > 1 && is_null($operands[1])) {
			$operation = 'op_unary_' . $this->operator;
		}
		else {
			$operation = 'op_' . $this->operator;
			if ($this->associativity == 'l') {
				$operands = array_reverse($operands);
			}
		}
		
		if (method_exists($operands[0], $operation)) {
			return $operands[0]->$operation(!empty($operands[1]) ? $operands[1] : null);
		}

		throw new SassScriptOperationException('Undefined operation "{operation}" for {what}',  array('{operation}'=>$operation, '{what}'=>get_class($operands[0])), SassScriptParser::$context->node);
	}

	/**
	 * 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 static function isa($subject) {
		return (preg_match(self::MATCH, $subject, $matches) ? trim($matches[0]) : false);
	}
}