',
'',
'',
' replace]
*/
protected $dictionary;
/**
* @var string Prefix used for dictionary keys
*/
protected $keyPrefix = '$';
/**
* @var integer Number of bytes each global substitution must save to be considered
*/
public $minSaving = 10;
/**
* @var array Associative array of [string => saving]
*/
protected $savings;
/**
* @var string
*/
protected $xsl;
/**
* Encode given stylesheet into a compact JavaScript representation
*
* @param string $xsl Original stylesheet
* @return string JavaScript representation of the compressed stylesheet
*/
public function encode($xsl)
{
$this->xsl = $xsl;
$this->estimateSavings();
$this->filterSavings();
$this->buildDictionary();
$str = $this->getCompressedStylesheet();
// Split the stylesheet's string into 2000 chars chunks to appease Google Closure Compiler
preg_match_all('(.{1,2000})su', $str, $matches);
$js = implode("+\n", array_map('json_encode', $matches[0]));
if (!empty($this->dictionary))
{
$js = '(' . $js . ').replace(' . $this->getReplacementRegexp() . ',function(k){return' . json_encode($this->dictionary) . '[k];})';
}
return $js;
}
/**
* Build a dictionary of all cost-effective string replacements
*
* @return void
*/
protected function buildDictionary()
{
$keys = $this->getAvailableKeys();
rsort($keys);
$this->dictionary = [];
arsort($this->savings);
foreach (array_keys($this->savings) as $str)
{
$key = array_pop($keys);
if (!$key)
{
break;
}
$this->dictionary[$key] = $str;
}
}
/**
* Estimate the savings of every possible string replacement
*
* @return void
*/
protected function estimateSavings()
{
$this->savings = [];
foreach ($this->getStringsFrequency() as $str => $cnt)
{
$len = strlen($str);
$originalCost = $cnt * $len;
$replacementCost = $cnt * 2;
$overhead = $len + 6;
$this->savings[$str] = $originalCost - ($replacementCost + $overhead);
}
}
/**
* Filter the savings according to the minSaving property
*
* @return void
*/
protected function filterSavings()
{
$this->savings = array_filter(
$this->savings,
function ($saving)
{
return ($saving >= $this->minSaving);
}
);
}
/**
* Return all the possible dictionary keys that are not present in the original stylesheet
*
* @return string[]
*/
protected function getAvailableKeys()
{
return array_diff($this->getPossibleKeys(), $this->getUnavailableKeys());
}
/**
* Return the stylesheet after dictionary replacements
*
* @return string
*/
protected function getCompressedStylesheet()
{
return strtr($this->xsl, array_flip($this->dictionary));
}
/**
* Return a list of possible dictionary keys
*
* @return string[]
*/
protected function getPossibleKeys()
{
$keys = [];
foreach (range('a', 'z') as $char)
{
$keys[] = $this->keyPrefix . $char;
}
return $keys;
}
/**
* Return a regexp that matches all used dictionary keys
*
* @return string
*/
protected function getReplacementRegexp()
{
return '/' . RegexpBuilder::fromList(array_keys($this->dictionary)) . '/g';
}
/**
* Return the frequency of all deduplicatable strings
*
* @return array Array of [string => frequency]
*/
protected function getStringsFrequency()
{
$regexp = '(' . implode('|', $this->deduplicateTargets) . ')S';
preg_match_all($regexp, $this->xsl, $matches);
return array_count_values($matches[0]);
}
/**
* Return the list of possible dictionary keys that appear in the original stylesheet
*
* @return string[]
*/
protected function getUnavailableKeys()
{
preg_match_all('(' . preg_quote($this->keyPrefix) . '.)', $this->xsl, $matches);
return array_unique($matches[0]);
}
}