First draft for the new extension feature

- Only system extensions can be loaded for the moment by adding them in the config.php
  file.
- Remove previous system (it will be added properly in the new system in the next step).

1 files changed, 150 insertions, 0 deletions

diff --git a/lib/Minz/ExtensionManager.php b/lib/Minz/ExtensionManager.php
new file mode 100644
index 000000000..ae648fe0d
--- /dev/null
+++ b/lib/Minz/ExtensionManager.php
@@ -0,0 +1,150 @@
+<?php
+
+/**
+ * An extension manager to load extensions present in EXTENSIONS_PATH.
+ */
+class Minz_ExtensionManager {
+	private static $ext_metaname = 'metadata.json';
+	private static $ext_entry_point = 'extension.php';
+	private static $ext_list = array();
+	private static $ext_list_enabled = array();
+
+	private static $ext_auto_enabled = array();
+
+	/**
+	 * Initialize the extension manager by loading extensions in EXTENSIONS_PATH.
+	 *
+	 * A valid extension is a directory containing metadata.json and
+	 * extension.php files.
+	 * metadata.json is a JSON structure where the only required fields are
+	 * `name` and `entry_point`.
+	 * extension.php should contain at least a class named <name>Extension where
+	 * <name> must match with the entry point in metadata.json. This class must
+	 * inherit from Minz_Extension class.
+	 */
+	public static function init() {
+		$list_potential_extensions = array_values(array_diff(
+			scandir(EXTENSIONS_PATH),
+			array('..', '.')
+		));
+
+		self::$ext_auto_enabled = Minz_Configuration::extensionsEnabled();
+
+		foreach ($list_potential_extensions as $ext_dir) {
+			$ext_pathname = EXTENSIONS_PATH . '/' . $ext_dir;
+			$metadata_filename = $ext_pathname . '/' . self::$ext_metaname;
+
+			// Try to load metadata file.
+			if (!file_exists($metadata_filename)) {
+				// No metadata file? Invalid!
+				continue;
+			}
+			$meta_raw_content = file_get_contents($metadata_filename);
+			$meta_json = json_decode($meta_raw_content, true);
+			if (!$meta_json || !self::is_valid_metadata($meta_json)) {
+				// metadata.json is not a json file? Invalid!
+				// or metadata.json is invalid (no required information), invalid!
+				Minz_Log::warning('`' . $metadata_filename . '` is not a valid metadata file');
+				continue;
+			}
+
+			$meta_json['path'] = $ext_pathname;
+
+			// Try to load extension itself
+			$extension = self::load($meta_json);
+			if (!is_null($extension)) {
+				self::register($extension);
+			}
+		}
+	}
+
+	/**
+	 * Indicates if the given parameter is a valid metadata array.
+	 *
+	 * Required fields are:
+	 * - `name`: the name of the extension
+	 * - `entry_point`: a class name to load the extension source code
+	 * If the extension class name is `TestExtension`, entry point will be `Test`.
+	 * `entry_point` must be composed of alphanumeric characters.
+	 *
+	 * @param $meta is an array of values.
+	 * @return true if the array is valid, false else.
+	 */
+	public static function is_valid_metadata($meta) {
+		return !(empty($meta['name']) ||
+		         empty($meta['entrypoint']) ||
+		         !ctype_alnum($meta['entrypoint']));
+	}
+
+	/**
+	 * Load the extension source code based on info metadata.
+	 *
+	 * @param $info an array containing information about extension.
+	 * @return an extension inheriting from Minz_Extension.
+	 */
+	public static function load($info) {
+		$entry_point_filename = $info['path'] . '/' . self::$ext_entry_point;
+		$ext_class_name = $info['entrypoint'] . 'Extension';
+
+		include($entry_point_filename);
+
+		// Test if the given extension class exists.
+		if (!class_exists($ext_class_name)) {
+			Minz_Log::warning('`' . $ext_class_name .
+			                  '` cannot be found in `' . $entry_point_filename . '`');
+			return null;
+		}
+
+		// Try to load the class.
+		$extension = null;
+		try {
+			$extension = new $ext_class_name($info);
+		} catch (Minz_ExtensionException $e) {
+			// We cannot load the extension? Invalid!
+			Minz_Log::warning('In `' . $metadata_filename . '`: ' . $e->getMessage());
+			return null;
+		}
+
+		// Test if class is correct.
+		if (!($extension instanceof Minz_Extension)) {
+			Minz_Log::warning('`' . $ext_class_name .
+			                  '` is not an instance of `Minz_Extension`');
+			return null;
+		}
+
+		return $extension;
+	}
+
+	/**
+	 * Add the extension to the list of the known extensions ($ext_list).
+	 *
+	 * If the extension is present in $ext_auto_enabled and if its type is "system",
+	 * it will be enabled in the same time.
+	 *
+	 * @param $ext a valid extension.
+	 */
+	public static function register($ext) {
+		$name = $ext->getName();
+		self::$ext_list[$name] = $ext;
+
+		if ($ext->getType() === 'system' &&
+				in_array($name, self::$ext_auto_enabled)) {
+			self::enable($ext->getName());
+		}
+	}
+
+	/**
+	 * Enable an extension so it will be called when necessary.
+	 *
+	 * The extension init() method will be called.
+	 *
+	 * @param $ext_name is the name of a valid extension present in $ext_list.
+	 */
+	public static function enable($ext_name) {
+		if (isset(self::$ext_list[$ext_name])) {
+			$ext = self::$ext_list[$ext_name];
+			self::$ext_list_enabled[$ext_name] = $ext;
+			$ext->init();
+		}
+	}
+}