Improve post stream

- Return all discussion post IDs from API requests which add/remove
posts, so the post stream updates appropriately. Related to #146
- Always unload posts that are two pages away, no matter how fast
you’re scrolling
- Retrieve posts from cache instead of reloading them
- Fix various bugs. Maybe #152, needs confirmation

src/Api/Actions/Discussions/UpdateAction.php

@@ -85,6 +85,17 @@ class UpdateAction extends SerializeResourceAction
             $discussion = $state->discussion;
         }
 
+        if ($posts = $discussion->getModifiedPosts()) {
+            $discussion->posts_ids = $discussion->postsVisibleTo($actor)->orderBy('time')->lists('id');
+
+            $discussion->posts = array_filter($posts, function ($post) {
+                return $post->exists;
+            });
+
+            $request->include = array_merge($request->include, ['posts']);
+            $request->link = array_merge($request->include, ['posts', 'posts.discussion', 'posts.user']);
+        }
+
         return $discussion;
     }
 }

src/Api/Actions/Posts/CreateAction.php

@@ -22,13 +22,14 @@ class CreateAction extends BaseCreateAction
      * @inheritdoc
      */
     public static $include = [
-        'user' => true
+        'user' => true,
+        'discussion' => true
     ];
 
     /**
      * @inheritdoc
      */
-    public static $link = [];
+    public static $link = ['discussion.posts'];
 
     /**
      * @inheritdoc
@@ -84,6 +85,9 @@ class CreateAction extends BaseCreateAction
             );
         }
 
+        $discussion = $post->discussion;
+        $discussion->posts_ids = $discussion->postsVisibleTo($actor)->orderBy('time')->lists('id');
+
         return $post;
     }
 }