library/HTMLPurifier/AttrDef/CSS/BackgroundPosition.php

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<?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

class HTMLPurifier_AttrDef_CSS_BackgroundPosition extends HTMLPurifier_AttrDef
{
    
    protected $length;
    protected $percentage;
    
    public function __construct() {
        $this->length     = new HTMLPurifier_AttrDef_CSS_Length();
        $this->percentage = new HTMLPurifier_AttrDef_CSS_Percentage();
    }
    
    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['c'] = false; // center
        $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];
                $keywords[$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[] = $keywords['h'];
        elseif (count($measures))   $ret[] = array_shift($measures);
        elseif ($keywords['c']) {
            $ret[] = $keywords['c'];
            $keywords['c'] = false; // prevent re-use: center = center center
        }
        
        if     ($keywords['v'])     $ret[] = $keywords['v'];
        elseif (count($measures))   $ret[] = array_shift($measures);
        elseif ($keywords['c'])     $ret[] = $keywords['c'];
        
        if (empty($ret)) return false;
        return implode(' ', $ret);
        
    }
    
}

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