Active compiled style files are being pruned away

.svnignore

@@ -1,3 +1,3 @@
 *.idea
-*.git
 .git*
+lib/vendor/lessphp/.git

lib/Configuration.class.php

@@ -109,4 +109,17 @@ public function getTtl()
 	{
 		return $this->ttl;
 	}
+
+    /**
+     * Sets the TTL fo a compiled CSS file
+     *
+     * @api
+     * @param $ttl
+     * @since 1.5.1
+     */
+    public function setTtl($ttl)
+    {
+        $this->ttl = (int)$ttl;
+    }
+
 }

lib/Garbagecollector.class.php

@@ -2,7 +2,17 @@
 
 class WPLessGarbagecollector
 {
-	protected $configuration;
+    /**
+     * @static
+     * @var int Max number of compiled versions of a same file to keep
+     */
+    public static $COMPILED_VERSIONS = 3;
+
+    /**
+     * @protected
+     * @var WPLessConfiguration
+     */
+    protected $configuration;
 
 	public function __construct(WPLessConfiguration $configuration)
 	{
@@ -16,6 +26,7 @@ public function __construct(WPLessConfiguration $configuration)
 	public function clean()
 	{
 		$outdated_files = $this->getOutdatedFiles($this->configuration->getTtl());
+        $this->filterVersions($outdated_files);
 
 		if (!empty($outdated_files))
 		{
@@ -55,6 +66,46 @@ protected function getOutdatedFiles($ttl)
 		return $outdated;
 	}
 
+    protected function filterVersions(array &$outdated_files)
+    {
+        $groups = array();
+        $keep = array();
+
+        // Grouping and collecting data
+        foreach ($outdated_files as $index => &$file)
+        {
+            $m = array();
+            preg_match_all('#^(?P<group>.+)-(?P<token>[^\-\.]+).css$#sU', $file, $m, PREG_SET_ORDER);
+
+            if (empty($m))
+            {
+                continue;
+            }
+
+            if (!isset($groups[ $m['group'] ]))
+            {
+                $groups[ $m['group'] ] = array();
+            }
+
+            $groups[ $m['group'] ][ $file ] = filemtime($file);
+        }
+
+        // Capping groups
+        foreach ($groups as &$versions)
+        {
+            arsort($versions);
+            $chunks = array_chunk($versions, self::$COMPILED_VERSIONS);
+
+            if (!empty($chunks[0]))
+            {
+                $keep = array_merge($keep, $chunks[0]);
+            }
+        }
+
+        // Returning the diff
+        return array_diff($outdated_files, $keep);
+    }
+
 	/**
 	 * Remove a bunch of files
 	 *