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<?php
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// The background-position value is an array containing two array for X and Y position correspondingly
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// each coordinate-position array, in its turn containes two values:
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// first, the numeric value of percentage or units
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// second, flag indication that this value is a percentage (true) or plain unit value (false)
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define('LENGTH_REGEXP',"(?:-?\d*\.?\d+(?:em|ex|px|in|cm|mm|pt|pc)\b|-?\d+(?:em|ex|px|in|cm|mm|pt|pc)\b)");
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define('PERCENTAGE_REGEXP',"\b\d+%");
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define('TEXT_REGEXP',"\b(?:top|bottom|left|right|center)\b");
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define('BG_POSITION_SUBVALUE_TYPE_HORZ',1);
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define('BG_POSITION_SUBVALUE_TYPE_VERT',2);
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class CSSBackgroundPosition extends CSSSubFieldProperty {
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  function get_property_code() {
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    return CSS_BACKGROUND_POSITION;
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  }
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  function get_property_name() {
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    return 'background-position';
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  }
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  function default_value() {
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    return new BackgroundPosition(0,true,
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                                  0,true);
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  }
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  function build_subvalue($value) {
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    if ($value === "left" ||
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        $value === "top") {
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      return array(0, true);
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    };
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    if ($value === "right" ||
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        $value === "bottom") {
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      return array(100, true);
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    };
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    if ($value === "center") {
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      return array(50, true);
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    };
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    if (substr($value, strlen($value)-1,1) === "%") {
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      return array((int)$value, true);
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    } else {
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      return array($value, false);
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    };
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  }
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  function build_value($x, $y) {
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    return array(CSSBackgroundPosition::build_subvalue($x),
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                 CSSBackgroundPosition::build_subvalue($y));
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  }
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  function detect_type($value) {
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    if ($value === "left" || $value === "right") { return BG_POSITION_SUBVALUE_TYPE_HORZ; };
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    if ($value === "top" || $value === "bottom") { return BG_POSITION_SUBVALUE_TYPE_VERT; };
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    return null;
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  }
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  // See CSS 2.1 'background-position' for description of possible values
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  //
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  function parse_in($value) {
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    if (preg_match("/(".LENGTH_REGEXP."|".PERCENTAGE_REGEXP."|".TEXT_REGEXP."|\b0\b)\s+(".LENGTH_REGEXP."|".PERCENTAGE_REGEXP."|".TEXT_REGEXP."|\b0\b)/", $value, $matches)) {
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      $x = $matches[1];
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      $y = $matches[2];
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      $type_x = CSSBackgroundPosition::detect_type($x);
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      $type_y = CSSBackgroundPosition::detect_type($y);
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      if (is_null($type_x) && is_null($type_y)) {
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        return CSSBackgroundPosition::build_value($x,$y);
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      };
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      if ($type_x == BG_POSITION_SUBVALUE_TYPE_HORZ ||
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          $type_y == BG_POSITION_SUBVALUE_TYPE_VERT) {
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        return CSSBackgroundPosition::build_value($x,$y);
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      };
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      return CSSBackgroundPosition::build_value($y,$x);
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    };
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    // These values should be processed separately at lastt
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    if (preg_match("/\b(top)\b/",$value))    { return array(array(50, true),  array(0, true)); };
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    if (preg_match("/\b(center)\b/",$value)) { return array(array(50, true),  array(50, true)); };
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    if (preg_match("/\b(bottom)\b/",$value)) { return array(array(50, true),  array(100, true)); };
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    if (preg_match("/\b(left)\b/",$value))   { return array(array(0, true),   array(50, true)); };
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    if (preg_match("/\b(right)\b/",$value))  { return array(array(100, true), array(50, true)); };
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    if (preg_match("/".LENGTH_REGEXP."|".PERCENTAGE_REGEXP."/", $value, $matches)) {
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      $x = $matches[0];
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      return CSSBackgroundPosition::build_value($x,"50%");
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    };
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    return null;
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  }
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  function parse($value) {
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    if ($value === 'inherit') {
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      return CSS_PROPERTY_INHERIT;
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    };
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    $value = CSSBackgroundPosition::parse_in($value);
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    return new BackgroundPosition($value[0][0], $value[0][1],
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                                  $value[1][0], $value[1][1]);
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  }
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}
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?>