fixes #4373, #1640

23 files changed, 1520 insertions, 526 deletions

diff --git a/core/AssetManager.php b/core/AssetManager.php
index ec850de0db..1104ed42d8 100644
--- a/core/AssetManager.php
+++ b/core/AssetManager.php
@@ -11,14 +11,19 @@
 namespace Piwik;
 
 use Exception;
-use JSMin;
-use lessc;
+use Piwik\AssetManager\UIAsset;
+use Piwik\AssetManager\UIAsset\InMemoryUIAsset;
+use Piwik\AssetManager\UIAsset\OnDiskUIAsset;
+use Piwik\AssetManager\UIAssetCacheBuster;
+use Piwik\AssetManager\UIAssetFetcher\JScriptUIAssetFetcher;
+use Piwik\AssetManager\UIAssetFetcher\StaticUIAssetFetcher;
+use Piwik\AssetManager\UIAssetFetcher\StylesheetUIAssetFetcher;
+use Piwik\AssetManager\UIAssetFetcher;
+use Piwik\AssetManager\UIAssetMerger\JScriptUIAssetMerger;
+use Piwik\AssetManager\UIAssetMerger\StylesheetUIAssetMerger;
+use Piwik\Plugin\Manager;
 use Piwik\Translate;
-
-/**
- * @see libs/jsmin/jsmin.php
- */
-require_once PIWIK_INCLUDE_PATH . '/libs/jsmin/jsmin.php';
+use Piwik\Config as PiwikConfig;
 
 /**
  * AssetManager is the class used to manage the inclusion of UI assets:
@@ -36,678 +41,361 @@ require_once PIWIK_INCLUDE_PATH . '/libs/jsmin/jsmin.php';
  * When set to 0, files will be included within a pair of files: 1 JavaScript
  * and 1 css file.
  *
+ * @method static \Piwik\AssetManager getInstance()
  * @package Piwik
  */
-class AssetManager
+class AssetManager extends Singleton
 {
     const MERGED_CSS_FILE = "asset_manager_global_css.css";
-    const MERGED_JS_FILE = "asset_manager_global_js.js";
-    const STYLESHEET_IMPORT_EVENT = "AssetManager.getStylesheetFiles";
-    const JAVASCRIPT_IMPORT_EVENT = "AssetManager.getJavaScriptFiles";
-    const MERGED_FILE_DIR = "tmp/assets/";
-    const COMPRESSED_FILE_LOCATION = "/tmp/assets/";
+    const MERGED_CORE_JS_FILE = "asset_manager_core_js.js";
+    const MERGED_NON_CORE_JS_FILE = "asset_manager_non_core_js.js";
 
     const CSS_IMPORT_DIRECTIVE = "<link rel=\"stylesheet\" type=\"text/css\" href=\"%s\" />\n";
     const JS_IMPORT_DIRECTIVE = "<script type=\"text/javascript\" src=\"%s\"></script>\n";
     const GET_CSS_MODULE_ACTION = "index.php?module=Proxy&action=getCss";
-    const GET_JS_MODULE_ACTION = "index.php?module=Proxy&action=getJs";
-    const MINIFIED_JS_RATIO = 100;
+    const GET_CORE_JS_MODULE_ACTION = "index.php?module=Proxy&action=getCoreJs";
+    const GET_NON_CORE_JS_MODULE_ACTION = "index.php?module=Proxy&action=getNonCoreJs";
 
     /**
-     * @param $file
-     * @param $less
-     * @internal param $mergedContent
-     * @return string
+     * @var UIAssetCacheBuster
      */
-    protected static function getCssContentFromFile($file, $less)
-    {
-        self::validateCssFile($file);
-
-        $fileLocation = self::getAbsoluteLocation($file);
-        $less->addImportDir(dirname($fileLocation));
-
-        $content = file_get_contents($fileLocation);
-        $content = self::rewriteCssPathsDirectives($file, $content);
-
-        return $content;
-    }
+    private $cacheBuster;
 
     /**
-     * Returns CSS file inclusion directive(s) using the markup <link>
-     *
-     * @return string
+     * @var UIAssetFetcher
      */
-    public static function getCssAssets()
-    {
-        return sprintf(self::CSS_IMPORT_DIRECTIVE, self::GET_CSS_MODULE_ACTION);
-    }
+    private $minimalStylesheetFetcher;
 
     /**
-     * Returns JS file inclusion directive(s) using the markup <script>
-     *
-     * @return string
+     * @var Theme
      */
-    public static function getJsAssets()
-    {
-        $result = "<script type=\"text/javascript\">\n" . Translate::getJavascriptTranslations() . "\n</script>";
+    private $theme;
 
-        if (self::isMergedAssetsDisabled()) {
-            // Individual includes mode
-            self::removeMergedAsset(self::MERGED_JS_FILE);
-            $result .= self::getIndividualJsIncludes();
-        } else {
-            $result .= sprintf(self::JS_IMPORT_DIRECTIVE, self::GET_JS_MODULE_ACTION);
-        }
+    function __construct()
+    {
+        $this->cacheBuster = UIAssetCacheBuster::getInstance();
+        $this->minimalStylesheetFetcher =  new StaticUIAssetFetcher(array('plugins/Zeitgeist/stylesheets/base.less'), array(), $this->theme);
 
-        return $result;
+        if(Manager::getInstance()->getThemeEnabled() != null)
+            $this->theme = new Theme();
     }
 
     /**
-     * Assets are cached in the browser and Piwik server returns 304 after initial download.
-     * when the Cache buster string changes, the assets will be re-generated
-     *
-     * @return string
+     * @param UIAssetCacheBuster $cacheBuster
      */
-    public static function generateAssetsCacheBuster()
+    public function setCacheBuster($cacheBuster)
     {
-        $currentGitHash = @file_get_contents(PIWIK_INCLUDE_PATH . '/.git/refs/heads/master');
-        $pluginList = md5(implode(",", \Piwik\Plugin\Manager::getInstance()->getLoadedPluginsName()));
-        $cacheBuster = md5(SettingsPiwik::getSalt() . $pluginList . PHP_VERSION . Version::VERSION . trim($currentGitHash));
-        return $cacheBuster;
+        $this->cacheBuster = $cacheBuster;
     }
 
     /**
-     * Generate the merged css file.
-     *
-     * @throws Exception if a file can not be opened in write mode
+     * @param UIAssetFetcher $minimalStylesheetFetcher
      */
-    private static function prepareMergedCssFile()
+    public function setMinimalStylesheetFetcher($minimalStylesheetFetcher)
     {
-        $mergedCssAlreadyGenerated = self::isGenerated(self::MERGED_CSS_FILE);
-        $isDevelopingPiwik = self::isMergedAssetsDisabled();
-
-        if ($mergedCssAlreadyGenerated && !$isDevelopingPiwik) {
-            return;
-        }
-
-        $files = self::getStylesheetFiles();
-        $less = self::makeLess();
-
-        // Loop through each css file
-        $mergedContent = "";
-        foreach ($files as $file) {
-            $mergedContent .= self::getCssContentFromFile($file, $less, $mergedContent);
-        }
-
-        $fileHash = md5($mergedContent);
-        $firstLineCompileHash = "/* compile_me_once=$fileHash */";
-
-        // Disable Merged Assets ==> Check on each request if file needs re-compiling
-        if ($mergedCssAlreadyGenerated
-            && !$isDevelopingPiwik
-        ) {
-            $mergedFile = self::MERGED_CSS_FILE;
-            $cacheIsValid = self::isFirstLineMatching($mergedFile, $firstLineCompileHash);
-            if($cacheIsValid) {
-                return;
-            }
-            // Some CSS file in the merge, has changed since last merged asset was generated
-            // Note: we do not detect changes in @import'ed LESS files
-        }
-
-        $mergedContent = $less->compile($mergedContent);
-
-        /**
-         * Triggered after all less stylesheets are compiled to CSS, minified and merged into
-         * one file, but before the generated CSS is written to disk.
-         * 
-         * This event can be used to modify merged CSS.
-         * 
-         * @param string &$mergedContent The merged and minified CSS.
-         */
-        Piwik::postEvent('AssetManager.filterMergedStylesheets', array(&$mergedContent));
-
-        $theme = new Theme;
-        $mergedContent = $theme->rewriteAssetsPathToTheme($mergedContent);
-
-        $mergedContent =
-            $firstLineCompileHash . "\n"
-            . "/* Piwik CSS file is compiled with Less. You may be interested in writing a custom Theme for Piwik! */\n"
-            . $mergedContent;
-
-        self::writeAssetToFile($mergedContent, self::MERGED_CSS_FILE);
+        $this->minimalStylesheetFetcher = $minimalStylesheetFetcher;
     }
 
-    protected static function makeLess()
+    /**
+     * @param Theme $theme
+     */
+    public function setTheme($theme)
     {
-        if (!class_exists("lessc")) {
-            throw new Exception("Less was added to composer during 2.0. ==> Execute this command to update composer packages: \$ php composer.phar install");
-        }
-        $less = new lessc;
-        return $less;
+        $this->theme = $theme;
     }
 
     /**
-     * Returns the base.less compiled to css
+     * Return CSS file inclusion directive(s) using the markup <link>
      *
      * @return string
      */
-    public static function getCompiledBaseCss()
+    public function getCssInclusionDirective()
     {
-        $file = '/plugins/Zeitgeist/stylesheets/base.less';
-        $less = self::makeLess();
-        $lessContent = self::getCssContentFromFile($file, $less);
-        $css = $less->compile($lessContent);
-        return $css;
+        return sprintf(self::CSS_IMPORT_DIRECTIVE, self::GET_CSS_MODULE_ACTION);
     }
 
-    /*
-     * Rewrite css url directives
-     * - rewrites relative paths
-     * - rewrite windows directory separator \\ to /
+    /**
+     * Return JS file inclusion directive(s) using the markup <script>
+     *
+     * @return string
      */
-    protected static function rewriteCssPathsDirectives($relativePath, $content)
+    public function getJsInclusionDirective()
     {
-        static $rootDirectoryLength = null;
-        if (is_null($rootDirectoryLength)) {
-            $rootDirectoryLength = self::countDirectoriesInPathToRoot();
-        }
+        $result = "<script type=\"text/javascript\">\n" . Translate::getJavascriptTranslations() . "\n</script>";
 
-        $baseDirectory = dirname($relativePath);
-        $content = preg_replace_callback(
-            "/(url\(['\"]?)([^'\")]*)/",
-            function ($matches) use ($rootDirectoryLength, $baseDirectory) {
-                $absolutePath = substr(realpath(PIWIK_DOCUMENT_ROOT . "/$baseDirectory/" . $matches[2]), $rootDirectoryLength);
-                $rewritten = str_replace('\\', '/', $absolutePath);
+        if ($this->isMergedAssetsDisabled()) {
 
-                if (is_file($rewritten)) { // only rewrite the URL if transforming it points to a valid file
-                    return $matches[1] . $rewritten;
-                } else {
-                    return $matches[1] . $matches[2];
-                }
-            },
-            $content
-        );
-        return $content;
-    }
+            $this->getMergedCoreJSAsset()->delete();
+            $this->getMergedNonCoreJSAsset()->delete();
 
-    protected static function countDirectoriesInPathToRoot()
-    {
-        $rootDirectory = realpath(PIWIK_DOCUMENT_ROOT);
-        if ($rootDirectory != '/' && substr_compare($rootDirectory, '/', -1)) {
-            $rootDirectory .= '/';
-        }
-        $rootDirectoryLen = strlen($rootDirectory);
-        return $rootDirectoryLen;
-    }
+            $result .= $this->getIndividualJsIncludes();
 
-    private static function writeAssetToFile($mergedContent, $name)
-    {
-        // Remove the previous file
-        self::removeMergedAsset($name);
-
-        // Tries to open the new file
-        $newFilePath = self::getAbsoluteMergedFileLocation($name);
-        $newFile = @fopen($newFilePath, "w");
+        } else {
 
-        if (!$newFile) {
-            throw new Exception ("The file : " . $newFile . " can not be opened in write mode.");
+            $result .= sprintf(self::JS_IMPORT_DIRECTIVE, self::GET_CORE_JS_MODULE_ACTION);
+            $result .= sprintf(self::JS_IMPORT_DIRECTIVE, self::GET_NON_CORE_JS_MODULE_ACTION);
         }
 
-        // Write the content in the new file
-        fwrite($newFile, $mergedContent);
-        fclose($newFile);
+        return $result;
     }
 
     /**
-     * Returns individual CSS file inclusion directive(s) using the markup <link>
+     * Return the base.less compiled to css
      *
-     * @return string
+     * @return UIAsset
      */
-    private static function getIndividualCssIncludes()
+    public function getCompiledBaseCss()
     {
-        $cssIncludeString = '';
-
-        $stylesheets = self::getStylesheetFiles();
+        $mergedAsset = new InMemoryUIAsset();
 
-        foreach ($stylesheets as $cssFile) {
+        $assetMerger = new StylesheetUIAssetMerger($mergedAsset, $this->minimalStylesheetFetcher, $this->cacheBuster);
 
-            self::validateCssFile($cssFile);
-            $cssIncludeString = $cssIncludeString . sprintf(self::CSS_IMPORT_DIRECTIVE, $cssFile);
-        }
+        $assetMerger->generateFile();
 
-        return $cssIncludeString;
+        return $mergedAsset;
     }
 
     /**
-     * Returns required CSS files
+     * Return the css merged file absolute location.
+     * If there is none, the generation process will be triggered.
      *
-     * @return Array
+     * @return UIAsset
      */
-    private static function getStylesheetFiles()
+    public function getMergedStylesheet()
     {
-        $stylesheets = array();
-
-        /**
-         * Triggered when gathering the list of all stylesheets (CSS and LESS) needed by
-         * Piwik and its plugins.
-         * 
-         * Plugins that have stylesheets should use this event to make those stylesheets
-         * load.
-         * 
-         * Stylesheets should be placed within a **stylesheets** subdirectory in your plugin's
-         * root directory.
-         * 
-         * _Note: While you are developing your plugin you should enable the config setting
-         * `[Debug] disable_merged_assets` so your stylesheets will be reloaded immediately
-         * after a change._
-         *
-         * **Example**
-         * 
-         *     public function getStylesheetFiles(&$stylesheets)
-         *     {
-         *         $stylesheets[] = "plugins/MyPlugin/stylesheets/myfile.less";
-         *         $stylesheets[] = "plugins/MyPlugin/stylesheets/myotherfile.css";
-         *     }
-         * 
-         * @param string[] &$stylesheets The list of stylesheet paths.
-         */
-        Piwik::postEvent(self::STYLESHEET_IMPORT_EVENT, array(&$stylesheets));
-
-        $stylesheets = self::sortCssFiles($stylesheets);
-
-        $theme = new Theme;
-        $themeStylesheet = $theme->getStylesheet();
-        if($themeStylesheet) {
-            $stylesheets[] = $themeStylesheet;
-        }
+        $mergedAsset = $this->getMergedStylesheetAsset();
 
-        return $stylesheets;
-    }
+        $assetFetcher = new StylesheetUIAssetFetcher(Manager::getInstance()->getLoadedPluginsName(), $this->theme);
 
-    /**
-     * Ensure CSS stylesheets are loaded in a particular order regardless of the order that plugins are loaded.
-     *
-     * @param array $stylesheets Array of CSS stylesheet files
-     * @return array
-     */
-    private static function sortCssFiles($stylesheets)
-    {
-        $priorityCssOrdered = array(
-            'libs/',
-            'plugins/CoreHome/stylesheets/color_manager.css', // must be before other Piwik stylesheets
-            'plugins/Zeitgeist/stylesheets/base.less',
-            'plugins/Zeitgeist/stylesheets/',
-            'plugins/',
-            'plugins/Dashboard/stylesheets/dashboard.less',
-            'tests/',
-        );
-
-        return self::prioritySort($priorityCssOrdered, $stylesheets);
+        $assetMerger = new StylesheetUIAssetMerger($mergedAsset, $assetFetcher, $this->cacheBuster);
+
+        $assetMerger->generateFile();
+
+        return $mergedAsset;
     }
 
     /**
-     * Check the validity of the css file
+     * Return the core js merged file absolute location.
+     * If there is none, the generation process will be triggered.
      *
-     * @param string $cssFile CSS file name
-     * @return boolean
-     * @throws Exception if a file can not be opened in write mode
+     * @return UIAsset
      */
-    private static function validateCssFile($cssFile)
+    public function getMergedCoreJavaScript()
     {
-        if (!self::assetIsReadable($cssFile)) {
-            throw new Exception("The css asset with 'href' = " . $cssFile . " is not readable");
-        }
+        return $this->getMergedJavascript($this->getCoreJScriptFetcher(), $this->getMergedCoreJSAsset());
     }
 
     /**
-     * Generate the merged js file.
+     * Return the non core js merged file absolute location.
+     * If there is none, the generation process will be triggered.
      *
-     * @throws Exception if a file can not be opened in write mode
+     * @return UIAsset
      */
-    private static function generateMergedJsFile()
+    public function getMergedNonCoreJavaScript()
     {
-        $mergedContent = self::getFirstLineOfMergedJs();
-
-        $files = self::getJsFiles();
-        foreach ($files as $file) {
-            self::validateJsFile($file);
-            $fileLocation = self::getAbsoluteLocation($file);
-            $content = file_get_contents($fileLocation);
-            if (!self::isMinifiedJs($content)) {
-                $content = JSMin::minify($content);
-            }
-            $mergedContent = $mergedContent . PHP_EOL . $content;
-        }
-        $mergedContent = str_replace("\n", "\r\n", $mergedContent);
-
-        /**
-         * Triggered after all the JavaScript files Piwik uses are minified and merged into a
-         * single file, but before the merged JavaScript is written to disk.
-         * 
-         * Plugins can use this event to modify merged JavaScript or do something else
-         * with it.
-         * 
-         * @param string &$mergedContent The minified and merged JavaScript.
-         */
-        Piwik::postEvent('AssetManager.filterMergedJavaScripts', array(&$mergedContent));
-
-        $theme = new Theme;
-        $mergedContent = $theme->rewriteAssetsPathToTheme($mergedContent);
-
-        self::writeAssetToFile($mergedContent, self::MERGED_JS_FILE);
+        return $this->getMergedJavascript($this->getNonCoreJScriptFetcher(), $this->getMergedNonCoreJSAsset());
     }
 
     /**
-     * Returns individual JS file inclusion directive(s) using the markup <script>
-     *
-     * @return string
+     * @param boolean $core
+     * @return string[]
      */
-    private static function getIndividualJsIncludes()
+    public function getLoadedPlugins($core)
     {
-        $jsIncludeString = '';
+        $loadedPlugins = array();
 
-        $jsFiles = self::getJsFiles();
-        foreach ($jsFiles as $jsFile) {
-            self::validateJsFile($jsFile);
-            $jsIncludeString = $jsIncludeString . sprintf(self::JS_IMPORT_DIRECTIVE, $jsFile);
+        foreach(Manager::getInstance()->getLoadedPluginsName() as $pluginName) {
+
+            $pluginIsCore = Manager::getInstance()->isPluginBundledWithCore($pluginName);
+
+            if(($pluginIsCore && $core) || (!$pluginIsCore && !$core))
+                $loadedPlugins[] = $pluginName;
         }
-        return $jsIncludeString;
+
+        return $loadedPlugins;
     }
 
     /**
-     * Returns required JS files
-     *
-     * @return Array
+     * Remove previous merged assets
      */
-    private static function getJsFiles()
+    public function removeMergedAssets($pluginName = false)
     {
-        $jsFiles = array();
-
-        /**
-         * Triggered when gathering the list of all JavaScript files needed by Piwik
-         * and its plugins.
-         * 
-         * Plugins that have their own JavaScript should use this event to make those
-         * files load in the browser.
-         * 
-         * JavaScript files should be placed within a **javascripts** subdirectory in your
-         * plugin's root directory.
-         * 
-         * _Note: While you are developing your plugin you should enable the config setting
-         * `[Debug] disable_merged_assets` so JavaScript files will be reloaded immediately
-         * after every change._
-         *
-         * **Example**
-         * 
-         *     public function getJsFiles(&$jsFiles)
-         *     {
-         *         $jsFiles[] = "plugins/MyPlugin/javascripts/myfile.js";
-         *         $jsFiles[] = "plugins/MyPlugin/javascripts/anotherone.js";
-         *     }
-         * 
-         * @param string[] $jsFiles The JavaScript files to load.
-         */
-        Piwik::postEvent(self::JAVASCRIPT_IMPORT_EVENT, array(&$jsFiles));
-
-        $theme = new Theme;
-        $jsInThemes = $theme->getJavaScriptFiles();
-        if(!empty($jsInThemes)) {
-            $jsFiles = array_merge($jsFiles, $jsInThemes);
+        $assetsToRemove = array($this->getMergedStylesheetAsset());
+
+        if($pluginName) {
+
+            if($this->pluginContainsJScriptAssets($pluginName)) {
+
+                PiwikConfig::getInstance()->init();
+                if(Manager::getInstance()->isPluginBundledWithCore($pluginName)) {
+
+                    $assetsToRemove[] = $this->getMergedCoreJSAsset();
+
+                } else {
+
+                    $assetsToRemove[] = $this->getMergedNonCoreJSAsset();
+                }
+            }
+
+        } else {
+
+            $assetsToRemove[] = $this->getMergedCoreJSAsset();
+            $assetsToRemove[] = $this->getMergedNonCoreJSAsset();
         }
 
-        $jsFiles = self::sortJsFiles($jsFiles);
-        return $jsFiles;
+        $this->removeAssets($assetsToRemove);
     }
 
     /**
-     * Ensure core JS (jQuery etc.) are loaded in a particular order regardless of the order that plugins are loaded.
+     * Check if the merged file directory exists and is writable.
      *
-     * @param array $jsFiles Arry of JavaScript files
-     * @return array
+     * @return string The directory location
+     * @throws Exception if directory is not writable.
      */
-    private static function sortJsFiles($jsFiles)
+    public function getAssetDirectory()
     {
-        $priorityJsOrdered = array(
-            'libs/jquery/jquery.js',
-            'libs/jquery/jquery-ui.js',
-            'libs/jquery/jquery.browser.js',
-            'libs/',
-            'plugins/Zeitgeist/javascripts/piwikHelper.js',
-            'plugins/Zeitgeist/javascripts/',
-            'plugins/CoreHome/javascripts/broadcast.js',
-            'plugins/',
-            'tests/',
-        );
-
-        return self::prioritySort($priorityJsOrdered, $jsFiles);
-    }
+        $mergedFileDirectory = PIWIK_USER_PATH . "/tmp/assets";
+        $mergedFileDirectory = SettingsPiwik::rewriteTmpPathWithHostname($mergedFileDirectory);
 
-    /**
-     * Check the validity of the js file
-     *
-     * @param string $jsFile JavaScript file name
-     * @return boolean
-     * @throws Exception if js file is not valid
-     */
-    private static function validateJsFile($jsFile)
-    {
-        if (!self::assetIsReadable($jsFile)) {
-            throw new Exception("The js asset with 'src' = " . $jsFile . " is not readable");
+        if (!is_dir($mergedFileDirectory)) {
+            Filesystem::mkdir($mergedFileDirectory);
         }
-    }
 
-    /**
-     * Returns the global option disable_merged_assets
-     *
-     * @return string
-     */
-    public static function isMergedAssetsDisabled()
-    {
-        return Config::getInstance()->Debug['disable_merged_assets'];
+        if (!is_writable($mergedFileDirectory)) {
+            throw new Exception("Directory " . $mergedFileDirectory . " has to be writable.");
+        }
+
+        return $mergedFileDirectory;
     }
 
     /**
-     * Returns the css merged file absolute location.
-     * If there is none, the generation process will be triggered.
+     * Return the global option disable_merged_assets
      *
-     * @return string The absolute location of the css merged file
+     * @return boolean
      */
-    public static function getMergedCssFileLocation()
+    public function isMergedAssetsDisabled()
     {
-        self::prepareMergedCssFile();
-        return self::getAbsoluteMergedFileLocation(self::MERGED_CSS_FILE);
+        return Config::getInstance()->Debug['disable_merged_assets'];
     }
 
     /**
-     * Returns the js merged file absolute location.
-     * If there is none, the generation process will be triggered.
-     *
-     * @return string The absolute location of the js merged file
+     * @param UIAssetFetcher $assetFetcher
+     * @param UIAsset $mergedAsset
+     * @return UIAsset
      */
-    public static function getMergedJsFileLocation()
+    private function getMergedJavascript($assetFetcher, $mergedAsset)
     {
-        $isGenerated = self::isGenerated(self::MERGED_JS_FILE);
+        $assetMerger = new JScriptUIAssetMerger($mergedAsset, $assetFetcher, $this->cacheBuster);
 
-        // Make sure the merged JS is re-generated if there are new commits
-        if($isGenerated) {
-            $expectedFirstLine = self::getFirstLineOfMergedJs();
-            $isGenerated = self::isFirstLineMatching(self::MERGED_JS_FILE, $expectedFirstLine);
-        }
-        if (!$isGenerated) {
-            self::generateMergedJsFile();
-        }
+        $assetMerger->generateFile();
 
-        return self::getAbsoluteMergedFileLocation(self::MERGED_JS_FILE);
+        return $mergedAsset;
     }
 
     /**
-     * Check if the provided merged file is generated
+     * Return individual JS file inclusion directive(s) using the markup <script>
      *
-     * @param string $filename filename of the merged asset
-     * @return boolean true is file exists and is readable, false otherwise
+     * @return string
      */
-    private static function isGenerated($filename)
+    private function getIndividualJsIncludes()
     {
-        return is_readable(self::getAbsoluteMergedFileLocation($filename));
+        return
+            $this->getIndividualJsIncludesFromAssetFetcher($this->getCoreJScriptFetcher()) .
+            $this->getIndividualJsIncludesFromAssetFetcher($this->getNonCoreJScriptFetcher());
     }
 
     /**
-     * Removes the previous merged file if it exists.
-     * Also tries to remove compressed version of the merged file.
-     *
-     * @param string $filename filename of the merged asset
-     * @see ProxyStaticFile::serveStaticFile(serveFile
-     * @throws Exception if the file couldn't be deleted
+     * @param UIAssetFetcher $assetFetcher
+     * @return string
      */
-    private static function removeMergedAsset($filename)
+    private function getIndividualJsIncludesFromAssetFetcher($assetFetcher)
     {
-        $isGenerated = self::isGenerated($filename);
-
-        if ($isGenerated) {
-            if (!unlink(self::getAbsoluteMergedFileLocation($filename))) {
-                throw new Exception("Unable to delete merged file : " . $filename . ". Please delete the file and refresh");
-            }
+        $jsIncludeString = '';
 
-            // Tries to remove compressed version of the merged file.
-            // See ProxyHttp::serverStaticFile() for more info on static file compression
-            $compressedFileLocation = PIWIK_USER_PATH . self::COMPRESSED_FILE_LOCATION . $filename;
-            $compressedFileLocation = SettingsPiwik::rewriteTmpPathWithHostname($compressedFileLocation);
+        foreach ($assetFetcher->getCatalog()->getAssets() as $jsFile) {
 
-            @unlink($compressedFileLocation . ".deflate");
-            @unlink($compressedFileLocation . ".gz");
+            $jsFile->validateFile();
+            $jsIncludeString = $jsIncludeString . sprintf(self::JS_IMPORT_DIRECTIVE, $jsFile->getRelativeLocation());
         }
+
+        return $jsIncludeString;
     }
 
-    /**
-     * Remove previous merged assets
-     */
-    public static function removeMergedAssets()
+    private function getCoreJScriptFetcher()
     {
-        self::removeMergedAsset(self::MERGED_CSS_FILE);
-        self::removeMergedAsset(self::MERGED_JS_FILE);
+        return new JScriptUIAssetFetcher($this->getLoadedPlugins(true), $this->theme);
     }
 
-    /**
-     * Check if asset is readable
-     *
-     * @param string $relativePath Relative path to file
-     * @return boolean
-     */
-    private static function assetIsReadable($relativePath)
+    private function getNonCoreJScriptFetcher()
     {
-        return is_readable(self::getAbsoluteLocation($relativePath));
+        return new JScriptUIAssetFetcher($this->getLoadedPlugins(false), $this->theme);
     }
 
     /**
-     * Check if the merged file directory exists and is writable.
-     *
-     * @return string The directory location
-     * @throws Exception if directory is not writable.
+     * @param string $pluginName
+     * @return boolean
      */
-    private static function getMergedFileDirectory()
+    private function pluginContainsJScriptAssets($pluginName)
     {
-        $mergedFileDirectory = PIWIK_USER_PATH . '/' . self::MERGED_FILE_DIR;
-        $mergedFileDirectory = SettingsPiwik::rewriteTmpPathWithHostname($mergedFileDirectory);
+        $fetcher = new JScriptUIAssetFetcher(array($pluginName), $this->theme);
 
-        if (!is_dir($mergedFileDirectory)) {
-            Filesystem::mkdir($mergedFileDirectory);
-        }
+        $assets = $fetcher->getCatalog()->getAssets();
 
-        if (!is_writable($mergedFileDirectory)) {
-            throw new Exception("Directory " . $mergedFileDirectory . " has to be writable.");
-        }
+        $plugin = Manager::getInstance()->getLoadedPlugin($pluginName);
 
-        return $mergedFileDirectory;
-    }
+        if($plugin->isTheme()) {
 
-    /**
-     * Builds the absolute location of the requested merged file
-     *
-     * @param string $mergedFile Name of the merge file
-     * @return string absolute location of the merged file
-     */
-    private static function getAbsoluteMergedFileLocation($mergedFile)
-    {
-        return self::getMergedFileDirectory() . $mergedFile;
+            $theme = Manager::getInstance()->getTheme($pluginName);
+
+            $javaScriptFiles = $theme->getJavaScriptFiles();
+
+            if(!empty($javaScriptFiles))
+                $assets = array_merge($assets, $javaScriptFiles);
+        }
+
+        return !empty($assets);
     }
 
     /**
-     * Returns the full path of an asset file
-     *
-     * @param string $relativePath Relative path to file
-     * @return string
+     * @param UIAsset[] $uiAssets
      */
-    private static function getAbsoluteLocation($relativePath)
+    private function removeAssets($uiAssets)
     {
-        // served by web server directly, so must be a public path
-        return PIWIK_DOCUMENT_ROOT . "/" . $relativePath;
+        foreach($uiAssets as $uiAsset) {
+            $uiAsset->delete();
+        }
     }
 
     /**
-     * Indicates if the provided JavaScript content has already been minified or not.
-     * The heuristic is based on a custom ratio : (size of file) / (number of lines).
-     * The threshold (100) has been found empirically on existing files :
-     * - the ratio never exceeds 50 for non-minified content and
-     * - it never goes under 150 for minified content.
-     *
-     * @param string $content Contents of the JavaScript file
-     * @return boolean
+     * @return UIAsset
      */
-    private static function isMinifiedJs($content)
+    private function getMergedStylesheetAsset()
     {
-        $lineCount = substr_count($content, "\n");
-        if ($lineCount == 0) {
-            return true;
-        }
-
-        $contentSize = strlen($content);
-
-        $ratio = $contentSize / $lineCount;
-
-        return $ratio > self::MINIFIED_JS_RATIO;
+        return $this->getMergedUIAsset(self::MERGED_CSS_FILE);
     }
 
     /**
-     * Sort files according to priority order. Duplicates are also removed.
-     *
-     * @param array $priorityOrder Ordered array of paths (first to last) serving as buckets
-     * @param array $files Unsorted array of files
-     * @return array
+     * @return UIAsset
      */
-    public static function prioritySort($priorityOrder, $files)
+    private function getMergedCoreJSAsset()
     {
-        $newFiles = array();
-        foreach ($priorityOrder as $filePattern) {
-            $newFiles = array_merge($newFiles, preg_grep('~^' . $filePattern . '~', $files));
-        }
-        return array_keys(array_flip($newFiles));
+        return $this->getMergedUIAsset(self::MERGED_CORE_JS_FILE);
     }
 
     /**
-     * @param $mergedFile
-     * @param $firstLineCompileHash
-     * @return bool
+     * @return UIAsset
      */
-    private static function isFirstLineMatching($mergedFile, $firstLineCompileHash)
+    private function getMergedNonCoreJSAsset()
     {
-        $pathMerged = self::getAbsoluteMergedFileLocation($mergedFile);
-        $f = fopen($pathMerged, 'r');
-        $firstLine = fgets($f);
-        fclose($f);
-        if (!empty($firstLine)
-            && trim($firstLine) == trim($firstLineCompileHash)
-        ) {
-            return true;
-        }
-        return false;
+        return $this->getMergedUIAsset(self::MERGED_NON_CORE_JS_FILE);
     }
 
     /**
-     * @return string
+     * @param string $fileName
+     * @return UIAsset
      */
-    private static function getFirstLineOfMergedJs()
+    private function getMergedUIAsset($fileName)
     {
-        return "/* Piwik Javascript - cb=" . self::generateAssetsCacheBuster() . "*/\n";
+        return new OnDiskUIAsset($this->getAssetDirectory(), $fileName);
     }
 }
\ No newline at end of file
diff --git a/core/AssetManager/UIAsset.php b/core/AssetManager/UIAsset.php
new file mode 100644
index 0000000000..00ba05cf74
--- /dev/null
+++ b/core/AssetManager/UIAsset.php
@@ -0,0 +1,63 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @package Piwik
+ */
+namespace Piwik\AssetManager;
+
+use Exception;
+
+abstract class UIAsset
+{
+    abstract public function validateFile();
+
+    /**
+     * @return string
+     */
+    abstract public function getAbsoluteLocation();
+
+    /**
+     * @return string
+     */
+    abstract public function getRelativeLocation();
+
+    /**
+     * @return string
+     */
+    abstract public function getBaseDirectory();
+
+    /**
+     * Removes the previous file if it exists.
+     * Also tries to remove compressed version of the file.
+     *
+     * @see ProxyStaticFile::serveStaticFile(serveFile
+     * @throws Exception if the file couldn't be deleted
+     */
+    abstract public function delete();
+
+    /**
+     * @param string $content
+     * @throws \Exception
+     */
+    abstract public function writeContent($content);
+
+    /**
+     * @return string
+     */
+    abstract public function getContent();
+
+    /**
+     * @return boolean
+     */
+    abstract public function exists();
+
+    /**
+     * @return int
+     */
+    abstract public function getModificationDate();
+}
diff --git a/core/AssetManager/UIAsset/InMemoryUIAsset.php b/core/AssetManager/UIAsset/InMemoryUIAsset.php
new file mode 100644
index 0000000000..3b5e8488f5
--- /dev/null
+++ b/core/AssetManager/UIAsset/InMemoryUIAsset.php
@@ -0,0 +1,65 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @package Piwik
+ */
+namespace Piwik\AssetManager\UIAsset;
+
+use Exception;
+use Piwik\AssetManager\UIAsset;
+
+class InMemoryUIAsset extends UIAsset
+{
+    private $content;
+
+    public function validateFile()
+    {
+        return;
+    }
+
+    public function getAbsoluteLocation()
+    {
+        throw new Exception('invalid operation');
+    }
+
+    public function getRelativeLocation()
+    {
+        throw new Exception('invalid operation');
+    }
+
+    public function getBaseDirectory()
+    {
+        throw new Exception('invalid operation');
+    }
+
+    public function delete()
+    {
+        $this->content = null;
+    }
+
+    public function exists()
+    {
+        return false;
+    }
+
+
+    public function writeContent($content)
+    {
+        $this->content = $content;
+    }
+
+    public function getContent()
+    {
+        return $this->content;
+    }
+
+    public function getModificationDate()
+    {
+        throw new Exception('invalid operation');
+    }
+}
diff --git a/core/AssetManager/UIAsset/OnDiskUIAsset.php b/core/AssetManager/UIAsset/OnDiskUIAsset.php
new file mode 100644
index 0000000000..bdda1119c2
--- /dev/null
+++ b/core/AssetManager/UIAsset/OnDiskUIAsset.php
@@ -0,0 +1,115 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @package Piwik
+ */
+namespace Piwik\AssetManager\UIAsset;
+
+use Exception;
+use Piwik\AssetManager\UIAsset;
+
+class OnDiskUIAsset extends UIAsset
+{
+    /**
+     * @var string
+     */
+    private $baseDirectory;
+
+    /**
+     * @var string
+     */
+    private $relativeLocation;
+
+    /**
+     * @param string $baseDirectory
+     * @param string $fileLocation
+     */
+    function __construct($baseDirectory, $fileLocation)
+    {
+        $this->baseDirectory = $baseDirectory;
+        $this->relativeLocation = $fileLocation;
+    }
+
+    public function getAbsoluteLocation()
+    {
+        return $this->baseDirectory . '/' . $this->relativeLocation;
+    }
+
+    public function getRelativeLocation()
+    {
+        return $this->relativeLocation;
+    }
+
+    public function getBaseDirectory()
+    {
+        return $this->baseDirectory;
+    }
+
+    public function validateFile()
+    {
+        if (!$this->assetIsReadable())
+            throw new Exception("The ui asset with 'href' = " . $this->getAbsoluteLocation() . " is not readable");
+    }
+
+    public function delete()
+    {
+        if ($this->exists()) {
+
+            if (!unlink($this->getAbsoluteLocation()))
+                throw new Exception("Unable to delete merged file : " . $this->getAbsoluteLocation() . ". Please delete the file and refresh");
+
+            // try to remove compressed version of the merged file.
+            @unlink($this->getAbsoluteLocation() . ".deflate");
+            @unlink($this->getAbsoluteLocation() . ".gz");
+        }
+    }
+
+    /**
+     * @param string $content
+     * @throws \Exception
+     */
+    public function writeContent($content)
+    {
+        $this->delete();
+
+        $newFile = @fopen($this->getAbsoluteLocation(), "w");
+
+        if (!$newFile)
+            throw new Exception ("The file : " . $newFile . " can not be opened in write mode.");
+
+        fwrite($newFile, $content);
+
+        fclose($newFile);
+    }
+
+    /**
+     * @return string
+     */
+    public function getContent()
+    {
+        return file_get_contents($this->getAbsoluteLocation());
+    }
+
+    public function exists()
+    {
+        return $this->assetIsReadable();
+    }
+
+    /**
+     * @return boolean
+     */
+    private function assetIsReadable()
+    {
+        return is_readable($this->getAbsoluteLocation());
+    }
+
+    public function getModificationDate()
+    {
+        return filemtime($this->getAbsoluteLocation());
+    }
+}
diff --git a/core/AssetManager/UIAssetCacheBuster.php b/core/AssetManager/UIAssetCacheBuster.php
new file mode 100644
index 0000000000..a8359442b3
--- /dev/null
+++ b/core/AssetManager/UIAssetCacheBuster.php
@@ -0,0 +1,47 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @method static \Piwik\AssetManager\UIAssetCacheBuster getInstance()
+ * @package Piwik
+ */
+namespace Piwik\AssetManager;
+
+use Piwik\Plugin\Manager;
+use Piwik\SettingsPiwik;
+use Piwik\Singleton;
+use Piwik\Version;
+
+class UIAssetCacheBuster extends Singleton
+{
+    /**
+     * Cache buster based on
+     *  - Piwik version
+     *  - Loaded plugins
+     *  - Super user salt
+     *  - Latest
+     *
+     * @param string[] $pluginNames
+     * @return string
+     */
+    public function piwikVersionBasedCacheBuster($pluginNames = false)
+    {
+        $currentGitHash = @file_get_contents(PIWIK_INCLUDE_PATH . '/.git/refs/heads/master');
+        $pluginList = md5(implode(",", !$pluginNames ? Manager::getInstance()->getLoadedPluginsName() : $pluginNames));
+        $cacheBuster = md5(SettingsPiwik::getSalt() . $pluginList . PHP_VERSION . Version::VERSION . trim($currentGitHash));
+        return $cacheBuster;
+    }
+
+    /**
+     * @param string $content
+     * @return string
+     */
+    public function md5BasedCacheBuster($content)
+    {
+        return md5($content);
+    }
+}
diff --git a/core/AssetManager/UIAssetCatalog.php b/core/AssetManager/UIAssetCatalog.php
new file mode 100644
index 0000000000..dc25553c8e
--- /dev/null
+++ b/core/AssetManager/UIAssetCatalog.php
@@ -0,0 +1,83 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @package Piwik
+ */
+namespace Piwik\AssetManager;
+
+class UIAssetCatalog
+{
+    /**
+     * @var UIAsset[]
+     */
+    private $uiAssets = array();
+
+    /**
+     * @var UIAssetCatalogSorter
+     */
+    private $catalogSorter;
+
+    /**
+     * @var string
+     */
+    private $concatenatedAssets;
+
+    /**
+     * @param UIAssetCatalogSorter $catalogSorter
+     */
+    function __construct($catalogSorter)
+    {
+        $this->catalogSorter = $catalogSorter;
+    }
+
+    /**
+     * @param UIAsset $uiAsset
+     */
+    public function addUIAsset($uiAsset)
+    {
+        if(!$this->assetAlreadyInCatalog($uiAsset)) {
+
+            $this->uiAssets[] = $uiAsset;
+            $this->resetConcatenatedAssets();
+        }
+    }
+
+    /**
+     * @return UIAsset[]
+     */
+    public function getAssets()
+    {
+        return $this->uiAssets;
+    }
+
+    /**
+     * @return UIAssetCatalog
+     */
+    public function getSortedCatalog()
+    {
+        return $this->catalogSorter->sortUIAssetCatalog($this);
+    }
+
+    private function resetConcatenatedAssets()
+    {
+        $this->concatenatedAssets = null;
+    }
+
+    /**
+     * @param UIAsset $uiAsset
+     * @return boolean
+     */
+    private function assetAlreadyInCatalog($uiAsset)
+    {
+        foreach($this->uiAssets as $existingAsset)
+            if($uiAsset->getAbsoluteLocation() == $existingAsset->getAbsoluteLocation())
+                return true;
+
+        return false;
+    }
+}
diff --git a/core/AssetManager/UIAssetCatalogSorter.php b/core/AssetManager/UIAssetCatalogSorter.php
new file mode 100644
index 0000000000..1f93a398e1
--- /dev/null
+++ b/core/AssetManager/UIAssetCatalogSorter.php
@@ -0,0 +1,61 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @package Piwik
+ */
+namespace Piwik\AssetManager;
+
+class UIAssetCatalogSorter
+{
+    /**
+     * @var string[]
+     */
+    private $priorityOrder;
+
+    /**
+     * @param string[] $priorityOrder
+     */
+    function __construct($priorityOrder)
+    {
+        $this->priorityOrder = $priorityOrder;
+    }
+
+    /**
+     * @param UIAssetCatalog $uiAssetCatalog
+     * @return UIAssetCatalog
+     */
+    public function sortUIAssetCatalog($uiAssetCatalog)
+    {
+        $sortedCatalog = new UIAssetCatalog($this);
+        foreach ($this->priorityOrder as $filePattern) {
+
+            $assetsMatchingPattern = array_filter($uiAssetCatalog->getAssets(), function($uiAsset) use ($filePattern)  {
+                return preg_match('~^' . $filePattern . '~', $uiAsset->getRelativeLocation());
+            });
+
+            foreach($assetsMatchingPattern as $assetMatchingPattern) {
+                $sortedCatalog->addUIAsset($assetMatchingPattern);
+            }
+        }
+
+        $this->addUnmatchedAssets($uiAssetCatalog, $sortedCatalog);
+
+        return $sortedCatalog;
+    }
+
+    /**
+     * @param UIAssetCatalog $uiAssetCatalog
+     * @param UIAssetCatalog $sortedCatalog
+     */
+    private function addUnmatchedAssets($uiAssetCatalog, $sortedCatalog)
+    {
+        foreach ($uiAssetCatalog->getAssets() as $uiAsset) {
+            $sortedCatalog->addUIAsset($uiAsset);
+        }
+    }
+}
diff --git a/core/AssetManager/UIAssetFetcher.php b/core/AssetManager/UIAssetFetcher.php
new file mode 100644
index 0000000000..21185014f7
--- /dev/null
+++ b/core/AssetManager/UIAssetFetcher.php
@@ -0,0 +1,121 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @package Piwik
+ */
+namespace Piwik\AssetManager;
+
+use Piwik\AssetManager\UIAsset\OnDiskUIAsset;
+use Piwik\Theme;
+
+abstract class UIAssetFetcher
+{
+    /**
+     * @var UIAssetCatalog
+     */
+    protected $catalog;
+
+    /**
+     * @var string[]
+     */
+    protected $fileLocations = array();
+
+    /**
+     * @var string[]
+     */
+    protected $plugins;
+
+    /**
+     * @var Theme
+     */
+    private $theme;
+
+    /**
+     * @param string[] $plugins
+     * @param Theme $theme
+     */
+    function __construct($plugins, $theme)
+    {
+        $this->plugins = $plugins;
+        $this->theme = $theme;
+    }
+
+    /**
+     * @return string[]
+     */
+    public function getPlugins()
+    {
+        return $this->plugins;
+    }
+
+    /**
+     * $return UIAssetCatalog
+     */
+    public function getCatalog()
+    {
+        if($this->catalog == null)
+            $this->createCatalog();
+
+        return $this->catalog;
+    }
+
+    abstract protected function retrieveFileLocations();
+
+    /**
+     * @return string[]
+     */
+    abstract protected function getPriorityOrder();
+
+    private function createCatalog()
+    {
+        $this->retrieveFileLocations();
+
+        $this->initCatalog();
+
+        $this->populateCatalog();
+
+        $this->sortCatalog();
+    }
+
+    private function initCatalog()
+    {
+        $catalogSorter = new UIAssetCatalogSorter($this->getPriorityOrder());
+        $this->catalog = new UIAssetCatalog($catalogSorter);
+    }
+
+    private function populateCatalog()
+    {
+        foreach ($this->fileLocations as $fileLocation) {
+
+            $newUIAsset = new OnDiskUIAsset($this->getBaseDirectory(), $fileLocation);
+            $this->catalog->addUIAsset($newUIAsset);
+        }
+    }
+
+    private function sortCatalog()
+    {
+        $this->catalog = $this->catalog->getSortedCatalog();
+    }
+
+    /**
+     * @return string
+     */
+    private function getBaseDirectory()
+    {
+        // served by web server directly, so must be a public path
+        return PIWIK_USER_PATH;
+    }
+
+    /**
+     * @return Theme
+     */
+    public function getTheme()
+    {
+        return $this->theme;
+    }
+}
diff --git a/core/AssetManager/UIAssetFetcher/JScriptUIAssetFetcher.php b/core/AssetManager/UIAssetFetcher/JScriptUIAssetFetcher.php
new file mode 100644
index 0000000000..3382fdabc6
--- /dev/null
+++ b/core/AssetManager/UIAssetFetcher/JScriptUIAssetFetcher.php
@@ -0,0 +1,85 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @package Piwik
+ */
+namespace Piwik\AssetManager\UIAssetFetcher;
+
+use Piwik\AssetManager\UIAssetFetcher;
+use Piwik\Piwik;
+use string;
+
+class JScriptUIAssetFetcher extends UIAssetFetcher
+{
+
+    protected function retrieveFileLocations()
+    {
+
+        if(!empty($this->plugins)) {
+
+            /**
+             * Triggered when gathering the list of all JavaScript files needed by Piwik
+             * and its plugins.
+             *
+             * Plugins that have their own JavaScript should use this event to make those
+             * files load in the browser.
+             *
+             * JavaScript files should be placed within a **javascripts** subdirectory in your
+             * plugin's root directory.
+             *
+             * _Note: While you are developing your plugin you should enable the config setting
+             * `[Debug] disable_merged_assets` so JavaScript files will be reloaded immediately
+             * after every change._
+             *
+             * **Example**
+             *
+             *     public function getJsFiles(&$jsFiles)
+             *     {
+             *         $jsFiles[] = "plugins/MyPlugin/javascripts/myfile.js";
+             *         $jsFiles[] = "plugins/MyPlugin/javascripts/anotherone.js";
+             *     }
+             *
+             * @param string[] $jsFiles The JavaScript files to load.
+             */
+             Piwik::postEvent('AssetManager.getJavaScriptFiles', array(&$this->fileLocations), null, $this->plugins);
+        }
+
+        $this->addThemeFiles();
+    }
+
+    protected function addThemeFiles()
+    {
+        if(in_array($this->getTheme()->getThemeName(), $this->plugins)) {
+
+            $jsInThemes = $this->getTheme()->getJavaScriptFiles();
+
+            if(!empty($jsInThemes)) {
+
+                foreach($jsInThemes as $jsFile) {
+
+                    $this->fileLocations[] = $jsFile;
+                }
+            }
+        }
+    }
+
+    protected function getPriorityOrder()
+    {
+        return array(
+            'libs/jquery/jquery.js',
+            'libs/jquery/jquery-ui.js',
+            'libs/jquery/jquery.browser.js',
+            'libs/',
+            'plugins/Zeitgeist/javascripts/piwikHelper.js',
+            'plugins/Zeitgeist/javascripts/',
+            'plugins/CoreHome/javascripts/broadcast.js',
+            'plugins/',
+            'tests/',
+        );
+    }
+}
diff --git a/core/AssetManager/UIAssetFetcher/StaticUIAssetFetcher.php b/core/AssetManager/UIAssetFetcher/StaticUIAssetFetcher.php
new file mode 100644
index 0000000000..981eac8204
--- /dev/null
+++ b/core/AssetManager/UIAssetFetcher/StaticUIAssetFetcher.php
@@ -0,0 +1,39 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @package Piwik
+ */
+namespace Piwik\AssetManager\UIAssetFetcher;
+
+use Piwik\AssetManager\UIAssetFetcher;
+
+class StaticUIAssetFetcher extends UIAssetFetcher
+{
+    /**
+     * @var string[]
+     */
+    private $priorityOrder;
+
+    function __construct($fileLocations, $priorityOrder, $theme)
+    {
+        parent::__construct(array(), $theme);
+
+        $this->fileLocations = $fileLocations;
+        $this->priorityOrder = $priorityOrder;
+    }
+
+    protected function retrieveFileLocations()
+    {
+
+    }
+
+    protected function getPriorityOrder()
+    {
+        return $this->priorityOrder;
+    }
+}
diff --git a/core/AssetManager/UIAssetFetcher/StylesheetUIAssetFetcher.php b/core/AssetManager/UIAssetFetcher/StylesheetUIAssetFetcher.php
new file mode 100644
index 0000000000..e5e6e7be0f
--- /dev/null
+++ b/core/AssetManager/UIAssetFetcher/StylesheetUIAssetFetcher.php
@@ -0,0 +1,70 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @package Piwik
+ */
+namespace Piwik\AssetManager\UIAssetFetcher;
+
+use Piwik\AssetManager\UIAssetFetcher;
+use Piwik\Piwik;
+
+class StylesheetUIAssetFetcher extends UIAssetFetcher
+{
+    protected function getPriorityOrder()
+    {
+        return array(
+            'libs/',
+            'plugins/CoreHome/stylesheets/color_manager.css', // must be before other Piwik stylesheets
+            'plugins/Zeitgeist/stylesheets/base.less',
+            'plugins/Zeitgeist/stylesheets/',
+            'plugins/',
+            'plugins/Dashboard/stylesheets/dashboard.less',
+            'tests/',
+        );
+    }
+
+    protected function retrieveFileLocations()
+    {
+        /**
+         * Triggered when gathering the list of all stylesheets (CSS and LESS) needed by
+         * Piwik and its plugins.
+         *
+         * Plugins that have stylesheets should use this event to make those stylesheets
+         * load.
+         *
+         * Stylesheets should be placed within a **stylesheets** subdirectory in your plugin's
+         * root directory.
+         *
+         * _Note: While you are developing your plugin you should enable the config setting
+         * `[Debug] disable_merged_assets` so your stylesheets will be reloaded immediately
+         * after a change._
+         *
+         * **Example**
+         *
+         *     public function getStylesheetFiles(&$stylesheets)
+         *     {
+         *         $stylesheets[] = "plugins/MyPlugin/stylesheets/myfile.less";
+         *         $stylesheets[] = "plugins/MyPlugin/stylesheets/myotherfile.css";
+         *     }
+         *
+         * @param string[] &$stylesheets The list of stylesheet paths.
+         */
+        Piwik::postEvent('AssetManager.getStylesheetFiles', array(&$this->fileLocations));
+
+        $this->addThemeFiles();
+    }
+
+    protected function addThemeFiles()
+    {
+        $themeStylesheet = $this->getTheme()->getStylesheet();
+
+        if($themeStylesheet) {
+            $this->fileLocations[] = $themeStylesheet;
+        }
+    }
+}
diff --git a/core/AssetManager/UIAssetMerger.php b/core/AssetManager/UIAssetMerger.php
new file mode 100644
index 0000000000..8e1ededd47
--- /dev/null
+++ b/core/AssetManager/UIAssetMerger.php
@@ -0,0 +1,212 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @package Piwik
+ */
+namespace Piwik\AssetManager;
+
+use Piwik\AssetManager\PiwikLessCompiler;
+use Piwik\AssetManager\UIAsset\StylesheetUIAsset;
+use Piwik\AssetManager;
+
+abstract class UIAssetMerger
+{
+    /**
+     * @var UIAssetFetcher
+     */
+    private $assetFetcher;
+
+    /**
+     * @var UIAsset
+     */
+    private $mergedAsset;
+
+    /**
+     * @var string
+     */
+    private $mergedContent;
+
+    /**
+     * @var UIAssetCacheBuster
+     */
+    protected $cacheBuster;
+
+    /**
+     * @param UIAsset $mergedAsset
+     * @param UIAssetFetcher $assetFetcher
+     * @param UIAssetCacheBuster $cacheBuster
+     */
+    function __construct($mergedAsset, $assetFetcher, $cacheBuster)
+    {
+        $this->mergedAsset = $mergedAsset;
+        $this->assetFetcher = $assetFetcher;
+        $this->cacheBuster = $cacheBuster;
+    }
+
+    public function generateFile()
+    {
+        if(!$this->shouldGenerate())
+            return;
+
+        $this->mergedContent = $this->getMergedAssets();
+
+        $this->postEvent($this->mergedContent);
+
+        $this->adjustPaths();
+
+        $this->addPreamble();
+
+        $this->writeContentToFile();
+    }
+
+    /**
+     * @return string
+     */
+    abstract protected function getMergedAssets();
+
+    /**
+     * @return string
+     */
+    abstract protected function generateCacheBuster();
+
+    /**
+     * @return string
+     */
+    abstract protected function getPreamble();
+
+    /**
+     * @return string
+     */
+    abstract protected function getFileSeparator();
+
+    /**
+     * @param UIAsset $uiAsset
+     * @return string
+     */
+    abstract protected function processFileContent($uiAsset);
+
+    /**
+     * @param string $mergedContent
+     */
+    abstract protected function postEvent(&$mergedContent);
+
+    protected function getConcatenatedAssets()
+    {
+        if(empty($this->mergedContent))
+            $this->concatenateAssets();
+
+        return $this->mergedContent;
+    }
+
+    private function concatenateAssets()
+    {
+        $mergedContent = '';
+
+        foreach ($this->getAssetCatalog()->getAssets() as $uiAsset) {
+
+            $uiAsset->validateFile();
+            $content = $this->processFileContent($uiAsset);
+
+            $mergedContent .= $this->getFileSeparator() . $content;
+        }
+
+        $this->mergedContent = $mergedContent;
+    }
+
+    /**
+     * @return string[]
+     */
+    protected function getPlugins()
+    {
+        return $this->assetFetcher->getPlugins();
+    }
+
+    /**
+     * @return UIAssetCatalog
+     */
+    protected function getAssetCatalog()
+    {
+        return $this->assetFetcher->getCatalog();
+    }
+
+    /**
+     * @return boolean
+     */
+    private function shouldGenerate()
+    {
+        if(!$this->mergedAsset->exists())
+            return true;
+
+        if($this->shouldCompareExistingVersion()) {
+
+            return !$this->isFileUpToDate();
+        }
+
+        return false;
+    }
+
+    /**
+     * @return boolean
+     */
+    private function isFileUpToDate()
+    {
+        $f = fopen($this->mergedAsset->getAbsoluteLocation(), 'r');
+        $firstLine = fgets($f);
+        fclose($f);
+
+        if (!empty($firstLine) && trim($firstLine) == trim($this->getCacheBusterValue())) {
+            return true;
+        }
+
+        // Some CSS file in the merge, has changed since last merged asset was generated
+        // Note: we do not detect changes in @import'ed LESS files
+        return false;
+    }
+
+    /**
+     * @return boolean
+     */
+    private function isMergedAssetsDisabled()
+    {
+        return AssetManager::getInstance()->isMergedAssetsDisabled();
+    }
+
+    private function adjustPaths()
+    {
+        $this->mergedContent = $this->assetFetcher->getTheme()->rewriteAssetsPathToTheme($this->mergedContent);
+    }
+
+    private function writeContentToFile()
+    {
+        $this->mergedAsset->writeContent($this->mergedContent);
+    }
+
+    /**
+     * @return string
+     */
+    protected function getCacheBusterValue()
+    {
+        if(empty($this->cacheBusterValue))
+            $this->cacheBusterValue = $this->generateCacheBuster();
+
+        return $this->cacheBusterValue;
+    }
+
+    private function addPreamble()
+    {
+        $this->mergedContent = $this->getPreamble() . $this->mergedContent;
+    }
+
+    /**
+     * @return boolean
+     */
+    private function shouldCompareExistingVersion()
+    {
+        return $this->isMergedAssetsDisabled();
+    }
+}
diff --git a/core/AssetManager/UIAssetMerger/JScriptUIAssetMerger.php b/core/AssetManager/UIAssetMerger/JScriptUIAssetMerger.php
new file mode 100644
index 0000000000..f501280ab1
--- /dev/null
+++ b/core/AssetManager/UIAssetMerger/JScriptUIAssetMerger.php
@@ -0,0 +1,91 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @package Piwik
+ */
+namespace Piwik\AssetManager\UIAssetMerger;
+
+use Piwik\AssetManager\UIAsset;
+use Piwik\AssetManager\UIAssetCacheBuster;
+use Piwik\AssetManager\UIAssetFetcher\JScriptUIAssetFetcher;
+use Piwik\AssetManager\UIAssetMerger;
+use Piwik\AssetManager;
+use Piwik\AssetManager\UIAssetMinifier;
+use Piwik\Piwik;
+
+class JScriptUIAssetMerger extends UIAssetMerger
+{
+    /**
+     * @var UIAssetMinifier
+     */
+    private $assetMinifier;
+
+    /**
+     * @param UIAsset $mergedAsset
+     * @param JScriptUIAssetFetcher $assetFetcher
+     * @param UIAssetCacheBuster $cacheBuster
+     */
+    function __construct($mergedAsset, $assetFetcher, $cacheBuster)
+    {
+        parent::__construct($mergedAsset, $assetFetcher, $cacheBuster);
+
+        $this->assetMinifier = UIAssetMinifier::getInstance();
+    }
+
+    protected function getMergedAssets()
+    {
+        $concatenatedAssets = $this->getConcatenatedAssets();
+
+        return str_replace("\n", "\r\n", $concatenatedAssets);
+    }
+
+    protected function generateCacheBuster()
+    {
+        $cacheBuster = $this->cacheBuster->piwikVersionBasedCacheBuster($this->getPlugins());
+        return "/* Piwik Javascript - cb=" . $cacheBuster . "*/\r\n";
+    }
+
+    protected function getPreamble()
+    {
+        return $this->getCacheBusterValue();
+    }
+
+    protected function postEvent(&$mergedContent)
+    {
+        $plugins = $this->getPlugins();
+
+        if(!empty($plugins)) {
+
+            /**
+             * Triggered after all the JavaScript files Piwik uses are minified and merged into a
+             * single file, but before the merged JavaScript is written to disk.
+             *
+             * Plugins can use this event to modify merged JavaScript or do something else
+             * with it.
+             *
+             * @param string $mergedContent The minified and merged JavaScript.
+             */
+            Piwik::postEvent('AssetManager.filterMergedJavaScripts', array(&$mergedContent), null, $plugins);
+        }
+    }
+
+    public function getFileSeparator()
+    {
+        return PHP_EOL;
+    }
+
+    protected function processFileContent($uiAsset)
+    {
+        $content = $uiAsset->getContent();
+
+        if (!$this->assetMinifier->isMinifiedJs($content))
+            $content = $this->assetMinifier->minifyJs($content);
+
+        return $content;
+    }
+}
diff --git a/core/AssetManager/UIAssetMerger/StylesheetUIAssetMerger.php b/core/AssetManager/UIAssetMerger/StylesheetUIAssetMerger.php
new file mode 100644
index 0000000000..ae02127448
--- /dev/null
+++ b/core/AssetManager/UIAssetMerger/StylesheetUIAssetMerger.php
@@ -0,0 +1,142 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @package Piwik
+ */
+namespace Piwik\AssetManager\UIAssetMerger;
+
+use Exception;
+use Piwik\AssetManager\UIAsset;
+use Piwik\AssetManager\UIAssetMerger;
+use Piwik\Piwik;
+use lessc;
+
+class StylesheetUIAssetMerger extends UIAssetMerger
+{
+    /**
+     * @var lessc
+     */
+    private $lessCompiler;
+
+    function __construct($mergedAsset, $assetFetcher, $cacheBuster)
+    {
+        parent::__construct($mergedAsset, $assetFetcher, $cacheBuster);
+
+        $this->lessCompiler = self::getLessCompiler();
+    }
+
+    protected function getMergedAssets()
+    {
+        foreach($this->getAssetCatalog()->getAssets() as $uiAsset) {
+            $this->lessCompiler->addImportDir(dirname($uiAsset->getAbsoluteLocation()));
+        }
+
+        return $this->lessCompiler->compile($this->getConcatenatedAssets());
+    }
+
+    /**
+     * @return lessc
+     * @throws Exception
+     */
+    private static function getLessCompiler()
+    {
+        if (!class_exists("lessc")) {
+            throw new Exception("Less was added to composer during 2.0. ==> Execute this command to update composer packages: \$ php composer.phar install");
+        }
+        $less = new lessc();
+        return $less;
+    }
+
+    protected function generateCacheBuster()
+    {
+        $fileHash = $this->cacheBuster->md5BasedCacheBuster($this->getConcatenatedAssets());
+        return "/* compile_me_once=$fileHash */";
+    }
+
+    protected function getPreamble()
+    {
+        return $this->getCacheBusterValue() . "\n"
+        . "/* Piwik CSS file is compiled with Less. You may be interested in writing a custom Theme for Piwik! */\n";
+    }
+
+    protected function postEvent(&$mergedContent)
+    {
+        /**
+         * Triggered after all less stylesheets are compiled to CSS, minified and merged into
+         * one file, but before the generated CSS is written to disk.
+         *
+         * This event can be used to modify merged CSS.
+         *
+         * @param string $mergedContent The merged and minified CSS.
+         */
+        Piwik::postEvent('AssetManager.filterMergedStylesheets', array(&$mergedContent));
+    }
+
+    public function getFileSeparator()
+    {
+        return '';
+    }
+
+    protected function processFileContent($uiAsset)
+    {
+        return $this->rewriteCssPathsDirectives($uiAsset);
+    }
+
+    /**
+     * Rewrite css url directives
+     * - rewrites paths defined relatively to their css/less definition file
+     * - rewrite windows directory separator \\ to /
+     *
+     * @param UIAsset $uiAsset
+     * @return string
+     */
+    private function rewriteCssPathsDirectives($uiAsset)
+    {
+        static $rootDirectoryLength = null;
+        if (is_null($rootDirectoryLength)) {
+            $rootDirectoryLength = self::countDirectoriesInPathToRoot($uiAsset);
+        }
+
+        $baseDirectory = dirname($uiAsset->getRelativeLocation());
+        $content = preg_replace_callback(
+            "/(url\(['\"]?)([^'\")]*)/",
+            function ($matches) use ($rootDirectoryLength, $baseDirectory) {
+
+                $absolutePath = realpath(PIWIK_USER_PATH . "/$baseDirectory/" . $matches[2]);
+
+                if($absolutePath) {
+
+                    $relativePath = substr($absolutePath, $rootDirectoryLength);
+
+                    $relativePath = str_replace('\\', '/', $relativePath);
+
+                    return $matches[1] . $relativePath;
+
+                } else {
+                    return $matches[1] . $matches[2];
+                }
+            },
+            $uiAsset->getContent()
+        );
+        return $content;
+    }
+
+    /**
+     * @param UIAsset $uiAsset
+     * @return int
+     */
+    protected function countDirectoriesInPathToRoot($uiAsset)
+    {
+        $rootDirectory = realpath($uiAsset->getBaseDirectory());
+        if ($rootDirectory != '/' && substr_compare($rootDirectory, '/', -1)) {
+            $rootDirectory .= '/';
+        }
+        $rootDirectoryLen = strlen($rootDirectory);
+        return $rootDirectoryLen;
+    }
+}
diff --git a/core/AssetManager/UIAssetMinifier.php b/core/AssetManager/UIAssetMinifier.php
new file mode 100644
index 0000000000..fe29f1ec61
--- /dev/null
+++ b/core/AssetManager/UIAssetMinifier.php
@@ -0,0 +1,67 @@
+<?php
+/**
+ * Piwik - Open source web analytics
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ *
+ * @category Piwik
+ * @method static \Piwik\AssetManager\UIAssetMinifier getInstance()
+ * @package Piwik
+ */
+namespace Piwik\AssetManager;
+
+use Exception;
+use Piwik\Singleton;
+use JShrink\Minifier;
+
+class UIAssetMinifier extends Singleton
+{
+    const MINIFIED_JS_RATIO = 100;
+
+    protected function __construct()
+    {
+        self::validateDependency();
+        parent::__construct();
+    }
+
+
+    /**
+     * Indicates if the provided JavaScript content has already been minified or not.
+     * The heuristic is based on a custom ratio : (size of file) / (number of lines).
+     * The threshold (100) has been found empirically on existing files :
+     * - the ratio never exceeds 50 for non-minified content and
+     * - it never goes under 150 for minified content.
+     *
+     * @param string $content Contents of the JavaScript file
+     * @return boolean
+     */
+    public function isMinifiedJs($content)
+    {
+        $lineCount = substr_count($content, "\n");
+        if ($lineCount == 0) {
+            return true;
+        }
+
+        $contentSize = strlen($content);
+
+        $ratio = $contentSize / $lineCount;
+
+        return $ratio > self::MINIFIED_JS_RATIO;
+    }
+
+    /**
+     * @param string $content
+     * @return string
+     */
+    public function minifyJs($content)
+    {
+        return Minifier::minify($content);
+    }
+
+    private static function validateDependency()
+    {
+        if (!class_exists("JShrink\Minifier"))
+            throw new Exception("JShrink dependency is managed using Composer.");
+    }
+}
diff --git a/core/Db/BatchInsert.php b/core/Db/BatchInsert.php
index 1a9563be95..89a003490f 100644
--- a/core/Db/BatchInsert.php
+++ b/core/Db/BatchInsert.php
@@ -61,7 +61,7 @@ class BatchInsert
      */
     public static function tableInsertBatch($tableName, $fields, $values, $throwException = false)
     {
-        $filePath = PIWIK_USER_PATH . '/' . AssetManager::MERGED_FILE_DIR . $tableName . '-' . Common::generateUniqId() . '.csv';
+        $filePath = PIWIK_USER_PATH . '/tmp/assets/' . $tableName . '-' . Common::generateUniqId() . '.csv';
         $filePath = SettingsPiwik::rewriteTmpPathWithHostname($filePath);
 
         if (Db::get()->hasBulkLoader()) {
diff --git a/core/Filesystem.php b/core/Filesystem.php
index aea8f5e1c8..37ea89e999 100644
--- a/core/Filesystem.php
+++ b/core/Filesystem.php
@@ -24,9 +24,9 @@ class Filesystem
      * Called on Core install, update, plugin enable/disable
      * Will clear all cache that could be affected by the change in configuration being made
      */
-    public static function deleteAllCacheOnUpdate()
+    public static function deleteAllCacheOnUpdate($pluginName = false)
     {
-        AssetManager::removeMergedAssets();
+        AssetManager::getInstance()->removeMergedAssets($pluginName);
         View::clearCompiledTemplates();
         Cache::deleteTrackerCache();
     }
diff --git a/core/Plugin.php b/core/Plugin.php
index 53fe0f8559..d2ce8d11dd 100644
--- a/core/Plugin.php
+++ b/core/Plugin.php
@@ -262,7 +262,7 @@ class Plugin
      *
      * @return bool
      */
-    final public function isTheme()
+    public function isTheme()
     {
         $info = $this->getInformation();
         return !empty($info['theme']) && (bool)$info['theme'];
diff --git a/core/Plugin/Manager.php b/core/Plugin/Manager.php
index 40ca5977ca..d067333b26 100644
--- a/core/Plugin/Manager.php
+++ b/core/Plugin/Manager.php
@@ -20,6 +20,7 @@ use Piwik\Plugin;
 use Piwik\Singleton;
 use Piwik\Translate;
 use Piwik\Updater;
+use Piwik\Theme;
 
 require_once PIWIK_INCLUDE_PATH . '/core/EventDispatcher.php';
 
@@ -219,7 +220,7 @@ class Manager extends Singleton
         PiwikConfig::getInstance()->forceSave();
         \Piwik\Settings\Manager::cleanupPluginSettings($pluginName);
 
-        Filesystem::deleteAllCacheOnUpdate();
+        $this->clearCache($pluginName);
 
         self::deletePluginFromFilesystem($pluginName);
         if ($this->isPluginInFilesystem($pluginName)) {
@@ -228,6 +229,14 @@ class Manager extends Singleton
         return true;
     }
 
+    /**
+     * @param string $pluginName
+     */
+    private function clearCache($pluginName)
+    {
+        Filesystem::deleteAllCacheOnUpdate($pluginName);
+    }
+
     public static function deletePluginFromFilesystem($plugin)
     {
         Filesystem::unlinkRecursive(PIWIK_INCLUDE_PATH . '/plugins/' . $plugin, $deleteRootToo = true);
@@ -255,7 +264,7 @@ class Manager extends Singleton
         $this->removePluginFromTrackerConfig($pluginName);
 
         PiwikConfig::getInstance()->forceSave();
-        Filesystem::deleteAllCacheOnUpdate();
+        $this->clearCache($pluginName);
 
         return $plugins;
     }
@@ -329,7 +338,7 @@ class Manager extends Singleton
         $this->updatePluginsConfig($plugins);
         PiwikConfig::getInstance()->forceSave();
 
-        Filesystem::deleteAllCacheOnUpdate();
+        $this->clearCache($pluginName);
 
         $this->pluginsToLoad[] = $pluginName;
     }
@@ -369,6 +378,22 @@ class Manager extends Singleton
         return $theme;
     }
 
+    /**
+     * @param string $themeName
+     * @throws \Exception
+     * @return Theme
+     */
+    public function getTheme($themeName)
+    {
+        $plugins = $this->getLoadedPlugins();
+
+        foreach ($plugins as $plugin)
+            if ($plugin->isTheme() && $plugin->getPluginName() == $themeName)
+                return new Theme($plugin);
+
+        throw new \Exception('Theme not found : ' . $themeName);
+    }
+
     public function getNumberOfActivatedPlugins()
     {
         $counter = 0;
diff --git a/core/ProxyHttp.php b/core/ProxyHttp.php
index b35d749342..692e8219bb 100644
--- a/core/ProxyHttp.php
+++ b/core/ProxyHttp.php
@@ -91,8 +91,7 @@ class ProxyHttp
                 // optional compression
                 $compressed = false;
                 $encoding = '';
-                $compressedFileLocation = PIWIK_USER_PATH . AssetManager::COMPRESSED_FILE_LOCATION . basename($file);
-                $compressedFileLocation = SettingsPiwik::rewriteTmpPathWithHostname($compressedFileLocation);
+                $compressedFileLocation = AssetManager::getInstance()->getAssetDirectory() . '/' . basename($file);
 
                 $phpOutputCompressionEnabled = ProxyHttp::isPhpOutputCompressed();
                 if (isset($_SERVER['HTTP_ACCEPT_ENCODING']) && !$phpOutputCompressionEnabled) {
diff --git a/core/Theme.php b/core/Theme.php
index 699783ae46..785d37382f 100644
--- a/core/Theme.php
+++ b/core/Theme.php
@@ -10,6 +10,8 @@
  */
 namespace Piwik;
 
+use Piwik\Plugin\Manager;
+
 /**
  * This class contains logic to make Themes work beautifully.
  *
@@ -23,10 +25,21 @@ class Theme
     /** @var \Piwik\Plugin  */
     private $theme;
 
-    public function __construct()
+    /**
+     * @var Plugin $plugin
+     */
+    public function __construct($plugin = false)
+    {
+        $this->createThemeFromPlugin($plugin ? $plugin : Manager::getInstance()->getThemeEnabled());
+    }
+
+    /**
+     * @param Plugin $plugin
+     */
+    private function createThemeFromPlugin($plugin)
     {
-        $this->theme = \Piwik\Plugin\Manager::getInstance()->getThemeEnabled();
-        $this->themeName = $this->theme->getPluginName();
+        $this->theme = $plugin;
+        $this->themeName = $plugin->getPluginName();
     }
 
     public function getStylesheet()
@@ -123,4 +136,11 @@ class Theme
         return $source;
     }
 
+    /**
+     * @return string
+     */
+    public function getThemeName()
+    {
+        return $this->themeName;
+    }
 }
\ No newline at end of file
diff --git a/core/Twig.php b/core/Twig.php
index 69a6501d90..3f15148985 100644
--- a/core/Twig.php
+++ b/core/Twig.php
@@ -104,9 +104,9 @@ class Twig
             $assetType = strtolower($params['type']);
             switch ($assetType) {
                 case 'css':
-                    return AssetManager::getCssAssets();
+                    return AssetManager::getInstance()->getCssInclusionDirective();
                 case 'js':
-                    return AssetManager::getJsAssets();
+                    return AssetManager::getInstance()->getJsInclusionDirective();
                 default:
                     throw new Exception("The twig function includeAssets 'type' parameter needs to be either 'css' or 'js'.");
             }
diff --git a/core/View.php b/core/View.php
index 105434e00a..9a9e105da0 100644
--- a/core/View.php
+++ b/core/View.php
@@ -11,6 +11,7 @@
 namespace Piwik;
 
 use Exception;
+use Piwik\AssetManager\UIAssetCacheBuster;
 use Piwik\Plugins\SitesManager\API as APISitesManager;
 use Piwik\Plugins\UsersManager\API as APIUsersManager;
 use Piwik\View\ViewInterface;
@@ -259,7 +260,7 @@ class View implements ViewInterface
 
     protected function applyFilter_cacheBuster($output)
     {
-        $cacheBuster = AssetManager::generateAssetsCacheBuster();
+        $cacheBuster = UIAssetCacheBuster::getInstance()->piwikVersionBasedCacheBuster();
         $tag = 'cb=' . $cacheBuster;
 
         $pattern = array(