Refactor frontend code to allow for extension of assets

- Simpler class naming:
    Frontend\CompilerFactory → Frontend\Assets
    Frontend\HtmlDocumentFactory → Frontend\Frontend
    Frontend\HtmlDocument → Frontend\Document

- Remove AssetInterface and simply collect callbacks in Frontend\Assets
  instead

- Remove ContentInterface because it serves no purpose (never type-
  hinted or type-checked)

- Commit and add asset URLs to the Document via a content callback
  instead of in the Document factory class itself

- Add translations and locale assets to Assets separate to the assets
  factory, as non-forum/admin asset bundles probably won't want them

- Update Frontend Extender to allow the creation of new asset bundles

- Make custom LESS validation listener a standalone class instead of
  extending RecompileFrontendAssets

src/Frontend/Content/Assets.php

@@ -0,0 +1,74 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Frontend\Content;
+
+use Flarum\Foundation\Application;
+use Flarum\Frontend\Compiler\CompilerInterface;
+use Flarum\Frontend\Document;
+use Psr\Http\Message\ServerRequestInterface as Request;
+
+class Assets
+{
+    protected $app;
+
+    /**
+     * @var \Flarum\Frontend\Assets
+     */
+    protected $assets;
+
+    public function __construct(Application $app)
+    {
+        $this->app = $app;
+    }
+
+    public function forFrontend(string $name)
+    {
+        $this->assets = $this->app->make('flarum.assets.'.$name);
+
+        return $this;
+    }
+
+    public function __invoke(Document $document, Request $request)
+    {
+        $locale = $request->getAttribute('locale');
+
+        $compilers = [
+            'js' => [$this->assets->makeJs(), $this->assets->makeLocaleJs($locale)],
+            'css' => [$this->assets->makeCss(), $this->assets->makeLocaleCss($locale)]
+        ];
+
+        if ($this->app->inDebugMode()) {
+            $this->commit(array_flatten($compilers));
+        }
+
+        $document->js = array_merge($document->js, $this->getUrls($compilers['js']));
+        $document->css = array_merge($document->css, $this->getUrls($compilers['css']));
+    }
+
+    private function commit(array $compilers)
+    {
+        foreach ($compilers as $compiler) {
+            $compiler->commit();
+        }
+    }
+
+    /**
+     * @param CompilerInterface[] $compilers
+     * @return string[]
+     */
+    private function getUrls(array $compilers)
+    {
+        return array_filter(array_map(function (CompilerInterface $compiler) {
+            return $compiler->getUrl();
+        }, $compilers));
+    }
+}

src/Frontend/Content/ContentInterface.php

@@ -1,24 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * (c) Toby Zerner <toby.zerner@gmail.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Flarum\Frontend\Content;
-
-use Flarum\Frontend\HtmlDocument;
-use Psr\Http\Message\ServerRequestInterface as Request;
-
-interface ContentInterface
-{
-    /**
-     * @param HtmlDocument $document
-     * @param Request $request
-     */
-    public function __invoke(HtmlDocument $document, Request $request);
-}

src/Frontend/Content/CorePayload.php

@@ -13,13 +13,13 @@ namespace Flarum\Frontend\Content;
 
 use Flarum\Api\Client;
 use Flarum\Api\Controller\ShowUserController;
-use Flarum\Frontend\HtmlDocument;
+use Flarum\Frontend\Document;
 use Flarum\Locale\LocaleManager;
 use Flarum\User\User;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\ServerRequestInterface as Request;
 
-class CorePayload implements ContentInterface
+class CorePayload
 {
     /**
      * @var LocaleManager
@@ -41,7 +41,7 @@ class CorePayload implements ContentInterface
         $this->api = $api;
     }
 
-    public function __invoke(HtmlDocument $document, Request $request)
+    public function __invoke(Document $document, Request $request)
     {
         $document->payload = array_merge(
             $document->payload,
@@ -49,7 +49,7 @@ class CorePayload implements ContentInterface
         );
     }
 
-    private function buildPayload(HtmlDocument $document, Request $request)
+    private function buildPayload(Document $document, Request $request)
     {
         $data = $this->getDataFromApiDocument($document->getForumApiDocument());
 

src/Frontend/Content/Layout.php

@@ -1,36 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * (c) Toby Zerner <toby.zerner@gmail.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Flarum\Frontend\Content;
-
-use Flarum\Frontend\HtmlDocument;
-use Psr\Http\Message\ServerRequestInterface as Request;
-
-class Layout implements ContentInterface
-{
-    /**
-     * @var string
-     */
-    protected $layoutView;
-
-    /**
-     * @param string $layoutView
-     */
-    public function __construct(string $layoutView)
-    {
-        $this->layoutView = $layoutView;
-    }
-
-    public function __invoke(HtmlDocument $document, Request $request)
-    {
-        $document->layoutView = $this->layoutView;
-    }
-}

src/Frontend/Content/Meta.php

@@ -11,18 +11,18 @@
 
 namespace Flarum\Frontend\Content;
 
-use Flarum\Frontend\HtmlDocument;
+use Flarum\Frontend\Document;
 use Psr\Http\Message\ServerRequestInterface as Request;
 
-class Meta implements ContentInterface
+class Meta
 {
-    public function __invoke(HtmlDocument $document, Request $request)
+    public function __invoke(Document $document, Request $request)
     {
         $document->meta = array_merge($document->meta, $this->buildMeta($document));
         $document->head = array_merge($document->head, $this->buildHead($document));
     }
 
-    private function buildMeta(HtmlDocument $document)
+    private function buildMeta(Document $document)
     {
         $forumApiDocument = $document->getForumApiDocument();
 
@@ -35,7 +35,7 @@ class Meta implements ContentInterface
         return $meta;
     }
 
-    private function buildHead(HtmlDocument $document)
+    private function buildHead(Document $document)
     {
         $head = [];