CSS minifier: additional functions to shorten some propertie's value

minify_css_same_values.php

// https://github.com/matthiasmullie/minify

/**
 * Merge same values to a shorter formula:
 * 		4 to 3, e.g.: "padding: 1px 2px 3px 2px"	->	"padding: 1px 2px 3px"
 * 		3 to 2, e.g.: "padding: 1px 2px 1px"		->	"padding: 1px 2px"
 * 		2 to 1, e.g.: "padding: 1px 1px"			->	"padding: 1px"
 * (if all the 4 values are the same, it will be shorten to 3, then to 2, then to 1. )
 * Care about calc values too.
 * Can only be applied to these properties: margin, padding, border-width and border-radius.
 * (Note: other properties can't be shorten (as far as I know): e.g.: 'background-position:50px' is NOT equal to 'background-position:50px 50px', but equal to 'background-position:50px center'!)
 * The border-radius property can be a bit more complex, the $before and $after params are to customize for this (see the shortenBorderRadius function).
 *
 * @param $css string		the css code to minify
 * @param $before string (optional)	the pattern what precedes the values to be shorten
 * @param $after string (optional)	the pattern what follow the values to be shorten
 *
 * @return string	the minified css code
 *
 */
private function mergeValues($css, $before = 'margin\s*\:|padding\s*\:|border\-width\s*\:|border\-radius\s*\:', $after = '[;}]')
{
  $value = '[^\s]+|calc\([^\)]+\)';
  // 4 to 3:
  $css = preg_replace('/('.$before.')\s*('.$value.')\s+('.$value.')\s+('.$value.')\s+\\3\s*(?='.$after.')/s', '\\1\\2 \\3 \\4', $css);
  // 3 to 2:
  $css = preg_replace('/('.$before.')\s*('.$value.')\s+('.$value.')\s+\\2\s*(?='.$after.')/s', '\\1\\2 \\3', $css);
  // 2 to 1:
  $css = preg_replace('/('.$before.')\s*('.$value.')\s+\\2\s*(?='.$after.')/s', '\\1\\2', $css);

  return $css;
}

/**
 * Handle border-radius special cases, cause by the '/'.
 * Try to shorten the values before and after the '/' separately.
 * Remove space from around the '/'.
 * Merge the two side of the '/' if equals.
 * e.g.: 'border-radius: 1px 2px 1px / 1px 2px 1px 2px'
 *    -> 'border-radius: 1px 2px'
 *
 * @param $css string	the css code to minify
 *
 * @return string	the minified css code
 *
 */
private function shortenBorderRadius($css)
{
  $css = $this->mergeValues($css, 'border\-radius\s*\:', '\/');	// merge before the '/'
  $css = $this->mergeValues($css, 'border\-radius\s*\:[^;}\/]+\/', '[;}]');	// merge after the '/'

  // remove space from around the '/'
  $css = preg_replace('~
    # find the target property
    (border\-radius\s*\:)\s*

      # values before the /
      ([^;}\/]+?)

      # the /
      \s*\/\s*

      # values after the /
      ([^;}]+?)\s*

      # end of property values
      (?=[;}])
      ~sx',
    '\\1\\2/\\3',$css);

  // merge the two side of the '/', if equals
  $css = preg_replace('~
    # find the target property
    (border\-radius\s*\:)

      # values before the /
      ([^;}\/]+?)

      # the /
      \/

      # values after the /, only match if equals what before that
      \\2

      # end of property values
      (?=[;}])
      ~sx',
    '\\1\\2',$css);

  return $css;
}

/* minify first with the library */
$minified = $this->mergeValues($minified);
$minified = $this->shortenBorderRadius($minified);