Yii extension composer installer WIP.

extensions/composer/yii/composer/Installer.php

+<?php
+/**
+ * @link http://www.yiiframework.com/
+ * @copyright Copyright (c) 2008 Yii Software LLC
+ * @license http://www.yiiframework.com/license/
+ */
+
+namespace yii\composer;
+
+use Composer\Package\PackageInterface;
+use Composer\Installer\LibraryInstaller;
+use Composer\Repository\InstalledRepositoryInterface;
+
+/**
+ * @author Qiang Xue <qiang.xue@gmail.com>
+ * @since 2.0
+ */
+class Installer extends LibraryInstaller
+{
+	/**
+	 * @inheritdoc
+	 */
+	public function supports($packageType)
+	{
+		return $packageType === 'yii2-extension';
+	}
+
+	/**
+	 * @inheritdoc
+	 */
+	public function install(InstalledRepositoryInterface $repo, PackageInterface $package)
+	{
+		parent::install($repo, $package);
+		$this->addPackage($package);
+	}
+
+	/**
+	 * @inheritdoc
+	 */
+	public function update(InstalledRepositoryInterface $repo, PackageInterface $initial, PackageInterface $target)
+	{
+		parent::update($repo, $initial, $target);
+		$this->removePackage($initial);
+		$this->addPackage($target);
+	}
+
+	/**
+	 * @inheritdoc
+	 */
+	public function uninstall(InstalledRepositoryInterface $repo, PackageInterface $package)
+	{
+		parent::uninstall($repo, $package);
+		$this->removePackage($package);
+	}
+
+	protected function addPackage(PackageInterface $package)
+	{
+		$extension = array('name' => $package->getPrettyName());
+
+		$root = $package->getPrettyName();
+		if ($targetDir = $package->getTargetDir()) {
+			$root .= '/' . trim($targetDir, '/');
+		}
+		$root = trim($root, '/');
+
+		$extra = $package->getExtra();
+
+		if (isset($extra['preinit']) && is_string($extra['preinit'])) {
+			$extension['preinit'] = "<vendor-dir>/$root/" . ltrim(str_replace('\\', '/', $extra['preinit']), '/');
+		}
+		if (isset($extra['init']) && is_string($extra['init'])) {
+			$extension['init'] = "<vendor-dir>/$root/" . ltrim(str_replace('\\', '/', $extra['init']), '/');
+		}
+
+		if (isset($extra['aliases']) && is_array($extra['aliases'])) {
+			foreach ($extra['aliases'] as $alias => $path) {
+				$extension['aliases']['@' . ltrim($alias, '@')] = "<vendor-dir>/$root/" . ltrim(str_replace('\\', '/', $path), '/');
+			}
+		}
+
+		if (!empty($aliases)) {
+			foreach ($aliases as $alias => $path) {
+				if (strncmp($alias, '@', 1) !== 0) {
+					$alias = '@' . $alias;
+				}
+				$path = trim(str_replace('\\', '/', $path), '/');
+				$extension['aliases'][$alias] = $root . '/' . $path;
+			}
+		}
+
+		$extensions = $this->loadExtensions();
+		$extensions[$package->getId()] = $extension;
+		$this->saveExtensions($extensions);
+	}
+
+	protected function removePackage(PackageInterface $package)
+	{
+		$packages = $this->loadExtensions();
+		unset($packages[$package->getId()]);
+		$this->saveExtensions($packages);
+	}
+
+	protected function loadExtensions()
+	{
+		$file = $this->vendorDir . '/yii-extensions.php';
+		if (!is_file($file)) {
+			return array();
+		}
+		$extensions = require($file);
+		/** @var string $vendorDir defined in yii-extensions.php */
+		$n = strlen($vendorDir);
+		foreach ($extensions as &$extension) {
+			if (isset($extension['aliases'])) {
+				foreach ($extension['aliases'] as $alias => $path) {
+					$extension['aliases'][$alias] = '<vendor-dir>' . substr($path, $n);
+				}
+			}
+			if (isset($extension['preinit'])) {
+				$extension['preinit'] = '<vendor-dir>' . substr($extension['preinit'], $n);
+			}
+			if (isset($extension['init'])) {
+				$extension['init'] = '<vendor-dir>' . substr($extension['init'], $n);
+			}
+		}
+		return $extensions;
+	}
+
+	protected function saveExtensions(array $extensions)
+	{
+		$file = $this->vendorDir . '/yii-extensions.php';
+		$array = str_replace("'<vendor-dir>", '$vendorDir . \'', var_export($extensions, true));
+		file_put_contents($file, "<?php\n\$vendorDir = __DIR__;\n\nreturn $array;\n");
+	}
+}

extensions/composer/yii/composer/InstallerPlugin.php

+<?php
+/**
+ * @link http://www.yiiframework.com/
+ * @copyright Copyright (c) 2008 Yii Software LLC
+ * @license http://www.yiiframework.com/license/
+ */
+
+namespace yii\composer;
+
+use Composer\Composer;
+use Composer\IO\IOInterface;
+use Composer\Plugin\PluginInterface;
+
+/**
+ * InstallerPlugin is the composer plugin that registers the Yii composer installer.
+ *
+ * @author Qiang Xue <qiang.xue@gmail.com>
+ * @since 2.0
+ */
+class InstallerPlugin implements PluginInterface
+{
+	/**
+	 * @inheritdoc
+	 */
+	public function activate(Composer $composer, IOInterface $io)
+	{
+		$installer = new Installer($io, $composer);
+		$composer->getInstallationManager()->addInstaller($installer);
+	}
+}