Performance: Actually make use of the translator cache

We had added a `storage/locale` directory to our skeleton, but we had
forgotten to hook it up with the translator. Enabling caching saves
parsing that locale YAML files on every pageload which should be good
for performance.

The locale cache will be cleared whenever an extension that uses the
`Locales` or `LanguagePack` extenders is enabled/disabled. If debug
mode is ON, then the caching mechanism will automatically check if any
of the loaded YAML files are dirty and update accordingly.

src/Extend/LanguagePack.php

@@ -18,7 +18,7 @@
 use InvalidArgumentException;
 use RuntimeException;
 
-class LanguagePack implements ExtenderInterface
+class LanguagePack implements ExtenderInterface, LifecycleInterface
 {
     public function extend(Container $container, Extension $extension = null)
     {
@@ -63,4 +63,14 @@ public function extend(Container $container, Extension $extension = null)
             }
         }
     }
+
+    public function onEnable(Container $container, Extension $extension)
+    {
+        $container->make('flarum.locales')->clearCache();
+    }
+
+    public function onDisable(Container $container, Extension $extension)
+    {
+        $container->make('flarum.locales')->clearCache();
+    }
 }

src/Extend/Locales.php

@@ -16,7 +16,7 @@
 use Flarum\Locale\LocaleManager;
 use Illuminate\Contracts\Container\Container;
 
-class Locales implements ExtenderInterface
+class Locales implements ExtenderInterface, LifecycleInterface
 {
     protected $directory;
 
@@ -46,4 +46,14 @@ public function extend(Container $container, Extension $extension = null)
             );
         }
     }
+
+    public function onEnable(Container $container, Extension $extension)
+    {
+        $container->make('flarum.locales')->clearCache();
+    }
+
+    public function onDisable(Container $container, Extension $extension)
+    {
+        $container->make('flarum.locales')->clearCache();
+    }
 }

src/Locale/LocaleManager.php

@@ -24,9 +24,15 @@ class LocaleManager
 
     protected $css = [];
 
-    public function __construct(Translator $translator)
+    /**
+     * @var string
+     */
+    protected $cacheDir;
+
+    public function __construct(Translator $translator, string $cacheDir = null)
     {
         $this->translator = $translator;
+        $this->cacheDir = $cacheDir;
     }
 
     public function getLocale(): string
@@ -106,4 +112,11 @@ public function setTranslator(Translator $translator)
     {
         $this->translator = $translator;
     }
+
+    public function clearCache()
+    {
+        if ($this->cacheDir) {
+            array_map('unlink', glob($this->cacheDir.'/*'));
+        }
+    }
 }

src/Locale/LocaleServiceProvider.php

@@ -13,10 +13,10 @@
 
 use Flarum\Event\ConfigureLocales;
 use Flarum\Foundation\AbstractServiceProvider;
+use Flarum\Foundation\Event\ClearingCache;
 use Flarum\Settings\SettingsRepositoryInterface;
 use Illuminate\Contracts\Events\Dispatcher;
 use Illuminate\Contracts\Translation\Translator as TranslatorContract;
-use Symfony\Component\Translation\MessageSelector;
 use Symfony\Component\Translation\TranslatorInterface;
 
 class LocaleServiceProvider extends AbstractServiceProvider
@@ -31,18 +31,34 @@ public function boot(Dispatcher $events)
         $locales->addLocale($this->getDefaultLocale(), 'Default');
 
         $events->dispatch(new ConfigureLocales($locales));
+
+        $events->listen(ClearingCache::class, function () use ($locales) {
+            $locales->clearCache();
+        });
     }
 
     /**
      * {@inheritdoc}
      */
     public function register()
     {
-        $this->app->singleton(LocaleManager::class);
+        $this->app->singleton(LocaleManager::class, function () {
+            return new LocaleManager(
+                $this->app->make('translator'),
+                $this->getCacheDir()
+            );
+        });
+
         $this->app->alias(LocaleManager::class, 'flarum.locales');
 
         $this->app->singleton('translator', function () {
-            $translator = new Translator($this->getDefaultLocale(), new MessageSelector());
+            $translator = new Translator(
+                $this->getDefaultLocale(),
+                null,
+                $this->getCacheDir(),
+                $this->app->inDebugMode()
+            );
+
             $translator->setFallbackLocales(['en']);
             $translator->addLoader('prefixed_yaml', new PrefixedYamlFileLoader());
 
@@ -59,4 +75,9 @@ private function getDefaultLocale(): string
 
         return $repo->get('default_locale', 'en');
     }
+
+    private function getCacheDir(): string
+    {
+        return $this->app->storagePath().'/locale';
+    }
 }