<?php

/**
 * Builtin functions
 *
 * @package Less
 * @subpackage function
 * @see http://lesscss.org/functions/
 */
class Less_Functions{

	public $env;
	public $currentFileInfo;

	function __construct($env, $currentFileInfo = null ){
		$this->env = $env;
		$this->currentFileInfo = $currentFileInfo;
	}


	/**
	 * @param string $op
	 */
    public static function operate( $op, $a, $b ){
		switch ($op) {
			case '+': return $a + $b;
			case '-': return $a - $b;
			case '*': return $a * $b;
			case '/': return $a / $b;
		}
	}

	public static function clamp($val, $max = 1){
		return min( max($val, 0), $max);
	}

	public static function fround( $value ){

		if( $value === 0 ){
			return $value;
		}

		if( Less_Parser::$options['numPrecision'] ){
			$p = pow(10, Less_Parser::$options['numPrecision']);
			return round( $value * $p) / $p;
		}
		return $value;
	}

    public static function number($n){

		if ($n instanceof Less_Tree_Dimension) {
			return floatval( $n->unit->is('%') ? $n->value / 100 : $n->value);
		} else if (is_numeric($n)) {
			return $n;
		} else {
			throw new Less_Exception_Compiler("color functions take numbers as parameters");
		}
	}

    public static function scaled($n, $size = 255 ){
		if( $n instanceof Less_Tree_Dimension && $n->unit->is('%') ){
			return (float)$n->value * $size / 100;
		} else {
			return Less_Functions::number($n);
		}
	}

	public function rgb ($r, $g, $b){
		return $this->rgba($r, $g, $b, 1.0);
	}

	public function rgba($r, $g, $b, $a){
		$rgb = array($r, $g, $b);
		$rgb = array_map(array('Less_Functions','scaled'),$rgb);

		$a = self::number($a);
		return new Less_Tree_Color($rgb, $a);
	}

	public function hsl($h, $s, $l){
		return $this->hsla($h, $s, $l, 1.0);
	}

	public function hsla($h, $s, $l, $a){

		$h = fmod(self::number($h), 360) / 360; // Classic % operator will change float to int
		$s = self::clamp(self::number($s));
		$l = self::clamp(self::number($l));
		$a = self::clamp(self::number($a));

		$m2 = $l <= 0.5 ? $l * ($s + 1) : $l + $s - $l * $s;

		$m1 = $l * 2 - $m2;

		return $this->rgba( self::hsla_hue($h + 1/3, $m1, $m2) * 255,
							self::hsla_hue($h, $m1, $m2) * 255,
							self::hsla_hue($h - 1/3, $m1, $m2) * 255,
							$a);
	}

	/**
	 * @param double $h
	 */
	public function hsla_hue($h, $m1, $m2){
		$h = $h < 0 ? $h + 1 : ($h > 1 ? $h - 1 : $h);
		if	  ($h * 6 < 1) return $m1 + ($m2 - $m1) * $h * 6;
		else if ($h * 2 < 1) return $m2;
		else if ($h * 3 < 2) return $m1 + ($m2 - $m1) * (2/3 - $h) * 6;
		else				 return $m1;
	}

	public function hsv($h, $s, $v) {
		return $this->hsva($h, $s, $v, 1.0);
	}

	/**
	 * @param double $a
	 */
	public function hsva($h, $s, $v, $a) {
		$h = ((Less_Functions::number($h) % 360) / 360 ) * 360;
		$s = Less_Functions::number($s);
		$v = Less_Functions::number($v);
		$a = Less_Functions::number($a);

		$i = floor(($h / 60) % 6);
		$f = ($h / 60) - $i;

		$vs = array( $v,
				  $v * (1 - $s),
				  $v * (1 - $f * $s),
				  $v * (1 - (1 - $f) * $s));

		$perm = array(array(0, 3, 1),
					array(2, 0, 1),
					array(1, 0, 3),
					array(1, 2, 0),
					array(3, 1, 0),
					array(0, 1, 2));

		return $this->rgba($vs[$perm[$i][0]] * 255,
						 $vs[$perm[$i][1]] * 255,
						 $vs[$perm[$i][2]] * 255,
						 $a);
	}

	public function hue($color){
		$c = $color->toHSL();
		return new Less_Tree_Dimension(Less_Parser::round($c['h']));
	}

	public function saturation($color){
		$c = $color->toHSL();
		return new Less_Tree_Dimension(Less_Parser::round($c['s'] * 100), '%');
	}

	public function lightness($color){
		$c = $color->toHSL();
		return new Less_Tree_Dimension(Less_Parser::round($c['l'] * 100), '%');
	}

	public function hsvhue( $color ){
		$hsv = $color->toHSV();
		return new Less_Tree_Dimension( Less_Parser::round($hsv['h']) );
	}


	public function hsvsaturation( $color ){
		$hsv = $color->toHSV();
		return new Less_Tree_Dimension( Less_Parser::round($hsv['s'] * 100), '%' );
	}

	public function hsvvalue( $color ){
		$hsv = $color->toHSV();
		return new Less_Tree_Dimension( Less_Parser::round($hsv['v'] * 100), '%' );
	}

	public function red($color) {
		return new Less_Tree_Dimension( $color->rgb[0] );
	}

	public function green($color) {
		return new Less_Tree_Dimension( $color->rgb[1] );
	}

	public function blue($color) {
		return new Less_Tree_Dimension( $color->rgb[2] );
	}

	public function alpha($color){
		$c = $color->toHSL();
		return new Less_Tree_Dimension($c['a']);
	}

	public function luma ($color) {
		return new Less_Tree_Dimension(Less_Parser::round( $color->luma() * $color->alpha * 100), '%');
	}

	public function luminance( $color ){
		$luminance =
			(0.2126 * $color->rgb[0] / 255)
		  + (0.7152 * $color->rgb[1] / 255)
		  + (0.0722 * $color->rgb[2] / 255);

		return new Less_Tree_Dimension(Less_Parser::round( $luminance * $color->alpha * 100), '%');
	}

	public function saturate($color, $amount = null){
		// filter: saturate(3.2);
		// should be kept as is, so check for color
		if( !property_exists($color,'rgb') ){
			return null;
		}
		$hsl = $color->toHSL();

		$hsl['s'] += $amount->value / 100;
		$hsl['s'] = self::clamp($hsl['s']);

		return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
	}

	/**
	 * @param Less_Tree_Dimension $amount
	 */
	public function desaturate($color, $amount){
		$hsl = $color->toHSL();

		$hsl['s'] -= $amount->value / 100;
		$hsl['s'] = self::clamp($hsl['s']);

		return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
	}



	public function lighten($color, $amount){
		$hsl = $color->toHSL();

		$hsl['l'] += $amount->value / 100;
		$hsl['l'] = self::clamp($hsl['l']);

		return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
	}

	public function darken($color, $amount){

		if( $color instanceof Less_Tree_Color ){
			$hsl = $color->toHSL();
			$hsl['l'] -= $amount->value / 100;
			$hsl['l'] = self::clamp($hsl['l']);

			return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
		}

		Less_Functions::Expected('color',$color);
	}

	public function fadein($color, $amount){
		$hsl = $color->toHSL();
		$hsl['a'] += $amount->value / 100;
		$hsl['a'] = self::clamp($hsl['a']);
		return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
	}

	public function fadeout($color, $amount){
		$hsl = $color->toHSL();
		$hsl['a'] -= $amount->value / 100;
		$hsl['a'] = self::clamp($hsl['a']);
		return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
	}

	public function fade($color, $amount){
		$hsl = $color->toHSL();

		$hsl['a'] = $amount->value / 100;
		$hsl['a'] = self::clamp($hsl['a']);
		return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
	}



	public function spin($color, $amount){
		$hsl = $color->toHSL();
		$hue = fmod($hsl['h'] + $amount->value, 360);

		$hsl['h'] = $hue < 0 ? 360 + $hue : $hue;

		return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
	}

	//
	// Copyright (c) 2006-2009 Hampton Catlin, Nathan Weizenbaum, and Chris Eppstein
	// http://sass-lang.com
	//

	/**
	 * @param Less_Tree_Color $color1
	 */
	public function mix($color1, $color2, $weight = null){
		if (!$weight) {
			$weight = new Less_Tree_Dimension('50', '%');
		}

		$p = $weight->value / 100.0;
		$w = $p * 2 - 1;
		$hsl1 = $color1->toHSL();
		$hsl2 = $color2->toHSL();
		$a = $hsl1['a'] - $hsl2['a'];

		$w1 = (((($w * $a) == -1) ? $w : ($w + $a) / (1 + $w * $a)) + 1) / 2;
		$w2 = 1 - $w1;

		$rgb = array($color1->rgb[0] * $w1 + $color2->rgb[0] * $w2,
					 $color1->rgb[1] * $w1 + $color2->rgb[1] * $w2,
					 $color1->rgb[2] * $w1 + $color2->rgb[2] * $w2);

		$alpha = $color1->alpha * $p + $color2->alpha * (1 - $p);

		return new Less_Tree_Color($rgb, $alpha);
	}

	public function greyscale($color){
		return $this->desaturate($color, new Less_Tree_Dimension(100));
	}


	public function contrast( $color, $dark = null, $light = null, $threshold = null){
		// filter: contrast(3.2);
		// should be kept as is, so check for color
		if( !property_exists($color,'rgb') ){
			return null;
		}
		if( !$light ){
			$light = $this->rgba(255, 255, 255, 1.0);
		}
		if( !$dark ){
			$dark = $this->rgba(0, 0, 0, 1.0);
		}
		//Figure out which is actually light and dark!
		if( $dark->luma() > $light->luma() ){
			$t = $light;
			$light = $dark;
			$dark = $t;
		}
		if( !$threshold ){
			$threshold = 0.43;
		} else {
			$threshold = Less_Functions::number($threshold);
		}

		if( $color->luma() < $threshold ){
			return $light;
		} else {
			return $dark;
		}
	}

	public function e ($str){
		if( is_string($str) ){
			return new Less_Tree_Anonymous($str);
		}
		return new Less_Tree_Anonymous($str instanceof Less_Tree_JavaScript ? $str->expression : $str->value);
	}

	public function escape ($str){

		$revert = array('%21'=>'!', '%2A'=>'*', '%27'=>"'",'%3F'=>'?','%26'=>'&','%2C'=>',','%2F'=>'/','%40'=>'@','%2B'=>'+','%24'=>'$');

		return new Less_Tree_Anonymous(strtr(rawurlencode($str->value), $revert));
	}


	/**
	 * todo: This function will need some additional work to make it work the same as less.js
	 *
	 */
	public function replace( $string, $pattern, $replacement, $flags = null ){
		$result = $string->value;

		$expr = '/'.str_replace('/','\\/',$pattern->value).'/';
		if( $flags && $flags->value){
			$expr .= self::replace_flags($flags->value);
		}

		$result = preg_replace($expr,$replacement->value,$result);


		if( property_exists($string,'quote') ){
			return new Less_Tree_Quoted( $string->quote, $result, $string->escaped);
		}
		return new Less_Tree_Quoted( '', $result );
	}

	public static function replace_flags($flags){
		$flags = str_split($flags,1);
		$new_flags = '';

		foreach($flags as $flag){
			switch($flag){
				case 'e':
				case 'g':
				break;

				default:
				$new_flags .= $flag;
				break;
			}
		}

		return $new_flags;
	}

	public function _percent(){
		$string = func_get_arg(0);

		$args = func_get_args();
		array_shift($args);
		$result = $string->value;

		foreach($args as $arg){
			if( preg_match('/%[sda]/i',$result, $token) ){
				$token = $token[0];
				$value = stristr($token, 's') ? $arg->value : $arg->toCSS();
				$value = preg_match('/[A-Z]$/', $token) ? urlencode($value) : $value;
				$result = preg_replace('/%[sda]/i',$value, $result, 1);
			}
		}
		$result = str_replace('%%', '%', $result);

		return new Less_Tree_Quoted( $string->quote , $result, $string->escaped);
	}

    public function unit( $val, $unit = null) {
		if( !($val instanceof Less_Tree_Dimension) ){
			throw new Less_Exception_Compiler('The first argument to unit must be a number' . ($val instanceof Less_Tree_Operation ? '. Have you forgotten parenthesis?' : '.') );
		}

		if( $unit ){
			if( $unit instanceof Less_Tree_Keyword ){
				$unit = $unit->value;
			} else {
				$unit = $unit->toCSS();
			}
		} else {
			$unit = "";
		}
		return new Less_Tree_Dimension($val->value, $unit );
    }

	public function convert($val, $unit){
		return $val->convertTo($unit->value);
	}

	public function round($n, $f = false) {

		$fraction = 0;
		if( $f !== false ){
			$fraction = $f->value;
		}

		return $this->_math('Less_Parser::round',null, $n, $fraction);
	}

	public function pi(){
		return new Less_Tree_Dimension(M_PI);
	}

	public function mod($a, $b) {
		return new Less_Tree_Dimension( $a->value % $b->value, $a->unit);
	}



	public function pow($x, $y) {
		if( is_numeric($x) && is_numeric($y) ){
			$x = new Less_Tree_Dimension($x);
			$y = new Less_Tree_Dimension($y);
		}elseif( !($x instanceof Less_Tree_Dimension) || !($y instanceof Less_Tree_Dimension) ){
			throw new Less_Exception_Compiler('Arguments must be numbers');
		}

		return new Less_Tree_Dimension( pow($x->value, $y->value), $x->unit );
	}

	// var mathFunctions = [{name:"ce ...
	public function ceil( $n ){		return $this->_math('ceil', null, $n); }
	public function floor( $n ){	return $this->_math('floor', null, $n); }
	public function sqrt( $n ){		return $this->_math('sqrt', null, $n); }
	public function abs( $n ){		return $this->_math('abs', null, $n); }

	public function tan( $n ){		return $this->_math('tan', '', $n);	}
	public function sin( $n ){		return $this->_math('sin', '', $n);	}
	public function cos( $n ){		return $this->_math('cos', '', $n);	}

	public function atan( $n ){		return $this->_math('atan', 'rad', $n);	}
	public function asin( $n ){		return $this->_math('asin', 'rad', $n);	}
	public function acos( $n ){		return $this->_math('acos', 'rad', $n);	}

	private function _math() {
		$args = func_get_args();
		$fn = array_shift($args);
		$unit = array_shift($args);

		if ($args[0] instanceof Less_Tree_Dimension) {

			if( $unit === null ){
				$unit = $args[0]->unit;
			}else{
				$args[0] = $args[0]->unify();
			}
			$args[0] = (float)$args[0]->value;
			return new Less_Tree_Dimension( call_user_func_array($fn, $args), $unit);
		} else if (is_numeric($args[0])) {
			return call_user_func_array($fn,$args);
		} else {
			throw new Less_Exception_Compiler("math functions take numbers as parameters");
		}
	}

	/**
	 * @param boolean $isMin
	 */
	private function _minmax( $isMin, $args ){

		$arg_count = count($args);

		if( $arg_count < 1 ){
			throw new Less_Exception_Compiler( 'one or more arguments required');
		}

		$j = null;
		$unitClone = null;
		$unitStatic = null;


		$order = array();	// elems only contains original argument values.
		$values = array();	// key is the unit.toString() for unified tree.Dimension values,
							// value is the index into the order array.


		for( $i = 0; $i < $arg_count; $i++ ){
			$current = $args[$i];
			if( !($current instanceof Less_Tree_Dimension) ){
				if( is_array($args[$i]->value) ){
					$args[] = $args[$i]->value;
				}
				continue;
			}

			if( $current->unit->toString() === '' && !$unitClone ){
				$temp = new Less_Tree_Dimension($current->value, $unitClone);
				$currentUnified = $temp->unify();
			}else{
				$currentUnified = $current->unify();
			}

			if( $currentUnified->unit->toString() === "" && !$unitStatic ){
				$unit = $unitStatic;
			}else{
				$unit = $currentUnified->unit->toString();
			}

			if( $unit !== '' && !$unitStatic || $unit !== '' && $order[0]->unify()->unit->toString() === "" ){
				$unitStatic = $unit;
			}

			if( $unit != '' && !$unitClone ){
				$unitClone = $current->unit->toString();
			}

			if( isset($values['']) && $unit !== '' && $unit === $unitStatic ){
				$j = $values[''];
			}elseif( isset($values[$unit]) ){
				$j = $values[$unit];
			}else{

				if( $unitStatic && $unit !== $unitStatic ){
					throw new Less_Exception_Compiler( 'incompatible types');
				}
				$values[$unit] = count($order);
				$order[] = $current;
				continue;
			}


			if( $order[$j]->unit->toString() === "" && $unitClone ){
				$temp = new Less_Tree_Dimension( $order[$j]->value, $unitClone);
				$referenceUnified = $temp->unifiy();
			}else{
				$referenceUnified = $order[$j]->unify();
			}
			if( ($isMin && $currentUnified->value < $referenceUnified->value) || (!$isMin && $currentUnified->value > $referenceUnified->value) ){
				$order[$j] = $current;
			}
		}

		if( count($order) == 1 ){
			return $order[0];
		}
		$args = array();
		foreach($order as $a){
			$args[] = $a->toCSS($this->env);
		}
		return new Less_Tree_Anonymous( ($isMin?'min(':'max(') . implode(Less_Environment::$_outputMap[','],$args).')');
	}

	public function min(){
		$args = func_get_args();
		return $this->_minmax( true, $args );
	}

	public function max(){
		$args = func_get_args();
		return $this->_minmax( false, $args );
	}

	public function getunit($n){
		return new Less_Tree_Anonymous($n->unit);
	}

	public function argb($color) {
		return new Less_Tree_Anonymous($color->toARGB());
	}

	public function percentage($n) {
		return new Less_Tree_Dimension($n->value * 100, '%');
	}

	public function color($n) {

		if( $n instanceof Less_Tree_Quoted ){
			$colorCandidate = $n->value;
			$returnColor = Less_Tree_Color::fromKeyword($colorCandidate);
			if( $returnColor ){
				return $returnColor;
			}
			if( preg_match('/^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})/',$colorCandidate) ){
				return new Less_Tree_Color(substr($colorCandidate, 1));
			}
			throw new Less_Exception_Compiler("argument must be a color keyword or 3/6 digit hex e.g. #FFF");
		} else {
			throw new Less_Exception_Compiler("argument must be a string");
		}
	}


	public function iscolor($n) {
		return $this->_isa($n, 'Less_Tree_Color');
	}

	public function isnumber($n) {
		return $this->_isa($n, 'Less_Tree_Dimension');
	}

	public function isstring($n) {
		return $this->_isa($n, 'Less_Tree_Quoted');
	}

	public function iskeyword($n) {
		return $this->_isa($n, 'Less_Tree_Keyword');
	}

	public function isurl($n) {
		return $this->_isa($n, 'Less_Tree_Url');
	}

	public function ispixel($n) {
		return $this->isunit($n, 'px');
	}

	public function ispercentage($n) {
		return $this->isunit($n, '%');
	}

	public function isem($n) {
		return $this->isunit($n, 'em');
	}

	/**
	 * @param string $unit
	 */
	public function isunit( $n, $unit ){
		return ($n instanceof Less_Tree_Dimension) && $n->unit->is( ( property_exists($unit,'value') ? $unit->value : $unit) ) ? new Less_Tree_Keyword('true') : new Less_Tree_Keyword('false');
	}

	/**
	 * @param string $type
	 */
	private function _isa($n, $type) {
		return is_a($n, $type) ? new Less_Tree_Keyword('true') : new Less_Tree_Keyword('false');
	}

	public function tint($color, $amount) {
		return $this->mix( $this->rgb(255,255,255), $color, $amount);
	}

	public function shade($color, $amount) {
		return $this->mix($this->rgb(0, 0, 0), $color, $amount);
	}

	public function extract($values, $index ){
		$index = (int)$index->value - 1; // (1-based index)
		// handle non-array values as an array of length 1
		// return 'undefined' if index is invalid
		if( property_exists($values,'value') && is_array($values->value) ){
			if( isset($values->value[$index]) ){
				return $values->value[$index];
			}
			return null;

		}elseif( (int)$index === 0 ){
			return $values;
		}

		return null;
	}

	public function length($values){
		$n = (property_exists($values,'value') && is_array($values->value)) ? count($values->value) : 1;
		return new Less_Tree_Dimension($n);
	}

	public function datauri($mimetypeNode, $filePathNode = null ) {

		$filePath = ( $filePathNode ? $filePathNode->value : null );
		$mimetype = $mimetypeNode->value;

		$args = 2;
		if( !$filePath ){
			$filePath = $mimetype;
			$args = 1;
		}

		$filePath = str_replace('\\','/',$filePath);
		if( Less_Environment::isPathRelative($filePath) ){

			if( Less_Parser::$options['relativeUrls'] ){
				$temp = $this->currentFileInfo['currentDirectory'];
			} else {
				$temp = $this->currentFileInfo['entryPath'];
			}

			if( !empty($temp) ){
				$filePath = Less_Environment::normalizePath(rtrim($temp,'/').'/'.$filePath);
			}

		}


		// detect the mimetype if not given
		if( $args < 2 ){

			/* incomplete
			$mime = require('mime');
			mimetype = mime.lookup(path);

			// use base 64 unless it's an ASCII or UTF-8 format
			var charset = mime.charsets.lookup(mimetype);
			useBase64 = ['US-ASCII', 'UTF-8'].indexOf(charset) < 0;
			if (useBase64) mimetype += ';base64';
			*/

			$mimetype = Less_Mime::lookup($filePath);

			$charset = Less_Mime::charsets_lookup($mimetype);
			$useBase64 = !in_array($charset,array('US-ASCII', 'UTF-8'));
			if( $useBase64 ){ $mimetype .= ';base64'; }

		}else{
			$useBase64 = preg_match('/;base64$/',$mimetype);
		}


		if( file_exists($filePath) ){
			$buf = @file_get_contents($filePath);
		}else{
			$buf = false;
		}


		// IE8 cannot handle a data-uri larger than 32KB. If this is exceeded
		// and the --ieCompat flag is enabled, return a normal url() instead.
		$DATA_URI_MAX_KB = 32;
		$fileSizeInKB = round( strlen($buf) / 1024 );
		if( $fileSizeInKB >= $DATA_URI_MAX_KB ){
			$url = new Less_Tree_Url( ($filePathNode ? $filePathNode : $mimetypeNode), $this->currentFileInfo);
			return $url->compile($this);
		}

		if( $buf ){
			$buf = $useBase64 ? base64_encode($buf) : rawurlencode($buf);
			$filePath = '"data:' . $mimetype . ',' . $buf . '"';
		}

		return new Less_Tree_Url( new Less_Tree_Anonymous($filePath) );
	}

	//svg-gradient
	public function svggradient( $direction ){

		$throw_message = 'svg-gradient expects direction, start_color [start_position], [color position,]..., end_color [end_position]';
		$arguments = func_get_args();

		if( count($arguments) < 3 ){
			throw new Less_Exception_Compiler( $throw_message );
		}

		$stops = array_slice($arguments,1);
		$gradientType = 'linear';
		$rectangleDimension = 'x="0" y="0" width="1" height="1"';
		$useBase64 = true;
		$directionValue = $direction->toCSS();


		switch( $directionValue ){
			case "to bottom":
				$gradientDirectionSvg = 'x1="0%" y1="0%" x2="0%" y2="100%"';
				break;
			case "to right":
				$gradientDirectionSvg = 'x1="0%" y1="0%" x2="100%" y2="0%"';
				break;
			case "to bottom right":
				$gradientDirectionSvg = 'x1="0%" y1="0%" x2="100%" y2="100%"';
				break;
			case "to top right":
				$gradientDirectionSvg = 'x1="0%" y1="100%" x2="100%" y2="0%"';
				break;
			case "ellipse":
			case "ellipse at center":
				$gradientType = "radial";
				$gradientDirectionSvg = 'cx="50%" cy="50%" r="75%"';
				$rectangleDimension = 'x="-50" y="-50" width="101" height="101"';
				break;
			default:
				throw new Less_Exception_Compiler( "svg-gradient direction must be 'to bottom', 'to right', 'to bottom right', 'to top right' or 'ellipse at center'" );
		}

		$returner = '<?xml version="1.0" ?>' .
			'<svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="100%" height="100%" viewBox="0 0 1 1" preserveAspectRatio="none">' .
			'<' . $gradientType . 'Gradient id="gradient" gradientUnits="userSpaceOnUse" ' . $gradientDirectionSvg . '>';

		for( $i = 0; $i < count($stops); $i++ ){
			if( is_object($stops[$i]) && property_exists($stops[$i],'value') ){
				$color = $stops[$i]->value[0];
				$position = $stops[$i]->value[1];
			}else{
				$color = $stops[$i];
				$position = null;
			}

			if( !($color instanceof Less_Tree_Color) || (!(($i === 0 || $i+1 === count($stops)) && $position === null) && !($position instanceof Less_Tree_Dimension)) ){
				throw new Less_Exception_Compiler( $throw_message );
			}
			if( $position ){
				$positionValue = $position->toCSS();
			}elseif( $i === 0 ){
				$positionValue = '0%';
			}else{
				$positionValue = '100%';
			}
			$alpha = $color->alpha;
			$returner .= '<stop offset="' . $positionValue . '" stop-color="' . $color->toRGB() . '"' . ($alpha < 1 ? ' stop-opacity="' . $alpha . '"' : '') . '/>';
		}

		$returner .= '</' . $gradientType . 'Gradient><rect ' . $rectangleDimension . ' fill="url(#gradient)" /></svg>';


		if( $useBase64 ){
			$returner = "'data:image/svg+xml;base64,".base64_encode($returner)."'";
		}else{
			$returner = "'data:image/svg+xml,".$returner."'";
		}

		return new Less_Tree_URL( new Less_Tree_Anonymous( $returner ) );
	}


	/**
	 * @param string $type
	 */
	private static function Expected( $type, $arg ){

		$debug = debug_backtrace();
		array_shift($debug);
		$last = array_shift($debug);
		$last = array_intersect_key($last,array('function'=>'','class'=>'','line'=>''));

		$message = 'Object of type '.get_class($arg).' passed to darken function. Expecting `'.$type.'`. '.$arg->toCSS().'. '.print_r($last,true);
		throw new Less_Exception_Compiler($message);

	}

	/**
	 * Php version of javascript's `encodeURIComponent` function
	 *
	 * @param string $string The string to encode
	 * @return string The encoded string
	 */
	public static function encodeURIComponent($string){
		$revert = array('%21' => '!', '%2A' => '*', '%27' => "'", '%28' => '(', '%29' => ')');
		return strtr(rawurlencode($string), $revert);
	}


	// Color Blending
	// ref: http://www.w3.org/TR/compositing-1

	public function colorBlend( $mode, $color1, $color2 ){
		$ab = $color1->alpha;	// backdrop
		$as = $color2->alpha;	// source
		$r = array();			// result

		$ar = $as + $ab * (1 - $as);
		for( $i = 0; $i < 3; $i++ ){
			$cb = $color1->rgb[$i] / 255;
			$cs = $color2->rgb[$i] / 255;
			$cr = call_user_func( $mode, $cb, $cs );
			if( $ar ){
				$cr = ($as * $cs + $ab * ($cb - $as * ($cb + $cs - $cr))) / $ar;
			}
			$r[$i] = $cr * 255;
		}

		return new Less_Tree_Color($r, $ar);
	}

	public function multiply($color1, $color2 ){
		return $this->colorBlend( array($this,'colorBlendMultiply'),  $color1, $color2 );
	}

	private function colorBlendMultiply($cb, $cs){
		return $cb * $cs;
	}

	public function screen($color1, $color2 ){
		return $this->colorBlend( array($this,'colorBlendScreen'),  $color1, $color2 );
	}

	private function colorBlendScreen( $cb, $cs){
		return $cb + $cs - $cb * $cs;
	}

	public function overlay($color1, $color2){
		return $this->colorBlend( array($this,'colorBlendOverlay'),  $color1, $color2 );
	}

	private function colorBlendOverlay($cb, $cs ){
		$cb *= 2;
		return ($cb <= 1)
			? $this->colorBlendMultiply($cb, $cs)
			: $this->colorBlendScreen($cb - 1, $cs);
	}

	public function softlight($color1, $color2){
		return $this->colorBlend( array($this,'colorBlendSoftlight'),  $color1, $color2 );
	}

	private function colorBlendSoftlight($cb, $cs ){
		$d = 1;
		$e = $cb;
		if( $cs > 0.5 ){
			$e = 1;
			$d = ($cb > 0.25) ? sqrt($cb)
				: ((16 * $cb - 12) * $cb + 4) * $cb;
		}
		return $cb - (1 - 2 * $cs) * $e * ($d - $cb);
	}

	public function hardlight($color1, $color2){
		return $this->colorBlend( array($this,'colorBlendHardlight'),  $color1, $color2 );
	}

	private function colorBlendHardlight( $cb, $cs ){
		return $this->colorBlendOverlay($cs, $cb);
	}

	public function difference($color1, $color2) {
		return $this->colorBlend( array($this,'colorBlendDifference'),  $color1, $color2 );
	}

	private function colorBlendDifference( $cb, $cs ){
		return abs($cb - $cs);
	}

	public function exclusion( $color1, $color2 ){
		return $this->colorBlend( array($this,'colorBlendExclusion'),  $color1, $color2 );
	}

	private function colorBlendExclusion( $cb, $cs ){
		return $cb + $cs - 2 * $cb * $cs;
	}

	public function average($color1, $color2){
		return $this->colorBlend( array($this,'colorBlendAverage'),  $color1, $color2 );
	}

	// non-w3c functions:
	public function colorBlendAverage($cb, $cs ){
		return ($cb + $cs) / 2;
	}

	public function negation($color1, $color2 ){
		return $this->colorBlend( array($this,'colorBlendNegation'),  $color1, $color2 );
	}

	public function colorBlendNegation($cb, $cs){
		return 1 - abs($cb + $cs - 1);
	}

	// ~ End of Color Blending

}
