<?php

/*
 * W3C says:
 * [ // adjective and number must be in correct order, even if
 * // you could switch them without introducing ambiguity.
 * // some browsers support that syntax
 * [
 * <percentage> | <length> | left | center | right
 * ]
 * [
 * <percentage> | <length> | top | center | bottom
 * ]?
 * ] |
 * [ // this signifies that the vertical and horizontal adjectives
 * // can be arbitrarily ordered, however, there can only be two,
 * // one of each, or none at all
 * [
 * left | center | right
 * ] ||
 * [
 * top | center | bottom
 * ]
 * ]
 * top, left = 0%
 * center, (none) = 50%
 * bottom, right = 100%
 */

/*
 * QuirksMode says:
 * keyword + length/percentage must be ordered correctly, as per W3C
 *
 * Internet Explorer and Opera, however, support arbitrary ordering. We
 * should fix it up.
 *
 * Minor issue though, not strictly necessary.
 */

// control freaks may appreciate the ability to convert these to
// percentages or something, but it's not necessary

/**
 * Validates the value of background-position.
 */
class HTMLPurifier_AttrDef_CSS_BackgroundPosition extends HTMLPurifier_AttrDef {
	
	/**
	 * @type HTMLPurifier_AttrDef_CSS_Length
	 */
	protected $length;
	
	/**
	 * @type HTMLPurifier_AttrDef_CSS_Percentage
	 */
	protected $percentage;
	public function __construct() {
		$this->length = new HTMLPurifier_AttrDef_CSS_Length ();
		$this->percentage = new HTMLPurifier_AttrDef_CSS_Percentage ();
	}
	
	/**
	 *
	 * @param string $string        	
	 * @param HTMLPurifier_Config $config        	
	 * @param HTMLPurifier_Context $context        	
	 * @return bool|string
	 */
	public function validate($string, $config, $context) {
		$string = $this->parseCDATA ( $string );
		$bits = explode ( ' ', $string );
		
		$keywords = array ();
		$keywords ['h'] = false; // left, right
		$keywords ['v'] = false; // top, bottom
		$keywords ['ch'] = false; // center (first word)
		$keywords ['cv'] = false; // center (second word)
		$measures = array ();
		
		$i = 0;
		
		$lookup = array (
				'top' => 'v',
				'bottom' => 'v',
				'left' => 'h',
				'right' => 'h',
				'center' => 'c' 
		);
		
		foreach ( $bits as $bit ) {
			if ($bit === '') {
				continue;
			}
			
			// test for keyword
			$lbit = ctype_lower ( $bit ) ? $bit : strtolower ( $bit );
			if (isset ( $lookup [$lbit] )) {
				$status = $lookup [$lbit];
				if ($status == 'c') {
					if ($i == 0) {
						$status = 'ch';
					} else {
						$status = 'cv';
					}
				}
				$keywords [$status] = $lbit;
				$i ++;
			}
			
			// test for length
			$r = $this->length->validate ( $bit, $config, $context );
			if ($r !== false) {
				$measures [] = $r;
				$i ++;
			}
			
			// test for percentage
			$r = $this->percentage->validate ( $bit, $config, $context );
			if ($r !== false) {
				$measures [] = $r;
				$i ++;
			}
		}
		
		if (! $i) {
			return false;
		} // no valid values were caught
		
		$ret = array ();
		
		// first keyword
		if ($keywords ['h']) {
			$ret [] = $keywords ['h'];
		} elseif ($keywords ['ch']) {
			$ret [] = $keywords ['ch'];
			$keywords ['cv'] = false; // prevent re-use: center = center center
		} elseif (count ( $measures )) {
			$ret [] = array_shift ( $measures );
		}
		
		if ($keywords ['v']) {
			$ret [] = $keywords ['v'];
		} elseif ($keywords ['cv']) {
			$ret [] = $keywords ['cv'];
		} elseif (count ( $measures )) {
			$ret [] = array_shift ( $measures );
		}
		
		if (empty ( $ret )) {
			return false;
		}
		return implode ( ' ', $ret );
	}
}

// vim: et sw=4 sts=4