FEATURE: Consolidate likes notifications. (#6879)

app/services/post_action_notifier.rb

@@ -76,16 +76,87 @@ class PostActionNotifier
     post = post_action.post
     return if post_action.user.blank?
 
-    alerter.create_notification(
-      post.user,
-      Notification.types[:liked],
-      post,
-      display_username: post_action.user.username,
-      post_action_id: post_action.id,
-      user_id: post_action.user_id
+    user_notifications = post.user.notifications
+
+    consolidation_window =
+      SiteSetting.likes_notification_consolidation_window_mins.minutes.ago
+
+    liked_by_user_notifications =
+      user_notifications
+        .get_liked_by(post_action.user)
+        .where("created_at > ?", consolidation_window)
+
+    user_liked_consolidated_notification =
+      user_notifications
+        .where(
+          "created_at > ? AND notification_type = ?",
+          consolidation_window,
+          Notification.types[:liked_consolidated]
+        )
+        .first
+
+    if user_liked_consolidated_notification
+      update_consolidated_liked_notification_count!(
+        user_liked_consolidated_notification
+      )
+    elsif (
+      liked_by_user_notifications.count >=
+      SiteSetting.likes_notification_consolidation_threshold
     )
+      create_consolidated_liked_notification!(
+        liked_by_user_notifications,
+        post,
+        post_action
+      )
+    else
+      alerter.create_notification(
+        post.user,
+        Notification.types[:liked],
+        post,
+        display_username: post_action.user.username,
+        post_action_id: post_action.id,
+        user_id: post_action.user_id
+      )
+    end
   end
 
+  def self.update_consolidated_liked_notification_count!(notification)
+    Notification.transaction do
+      data = JSON.parse(notification.data)
+      data["count"] += 1
+
+      notification.update!(
+        data: data.to_json,
+        read: false
+      )
+    end
+  end
+  private_class_method :update_consolidated_liked_notification_count!
+
+  def self.create_consolidated_liked_notification!(notifications,
+                                                  post,
+                                                  post_action)
+
+    Notification.transaction do
+      timestamp = notifications.last.created_at
+
+      Notification.create!(
+        notification_type: Notification.types[:liked_consolidated],
+        user_id: post.user_id,
+        data: {
+          username: post_action.user.username,
+          display_username: post_action.user.username,
+          count: notifications.count + 1
+        }.to_json,
+        updated_at: timestamp,
+        created_at: timestamp
+      )
+
+      notifications.delete_all
+    end
+  end
+  private_class_method :create_consolidated_liked_notification!
+
   def self.after_create_post_revision(post_revision)
     return if @disabled