feat(chat): notify message add/removal with pubsub

lib/slax/chat.ex

@@ -10,6 +10,8 @@ defmodule Slax.Chat do
   alias Slax.Chat.Room
   alias Slax.Repo
 
+  @pubsub Slax.PubSub
+
   def create_room(attrs) do
     %Room{}
     |> change_room(attrs)
@@ -53,9 +55,13 @@ defmodule Slax.Chat do
   end
 
   def create_message(room, user, attrs) do
-    %Message{room: room, user: user}
-    |> change_message(attrs)
-    |> Repo.insert()
+    with {:ok, message} <-
+           %Message{room: room, user: user}
+           |> change_message(attrs)
+           |> Repo.insert() do
+      Phoenix.PubSub.broadcast!(@pubsub, topic(room), {:new_message, message})
+      {:ok, message}
+    end
   end
 
   def change_message(message, attrs \\ %{}) do
@@ -63,8 +69,24 @@ defmodule Slax.Chat do
   end
 
   def delete_message_by_id(message_id, %User{id: user_id}) do
-    Message
-    |> Repo.get_by(id: message_id, user_id: user_id)
-    |> Repo.delete()
+    with {:ok, message} <-
+           Message
+           |> Repo.get_by(id: message_id, user_id: user_id)
+           |> Repo.delete() do
+      Phoenix.PubSub.broadcast!(@pubsub, topic(message.room_id), {:deleted_message, message})
+      {:ok, message}
+    end
   end
+
+  def subscribe_to_room(room) do
+    Phoenix.PubSub.subscribe(@pubsub, topic(room))
+  end
+
+  def unsubscribe_from_room(room) do
+    Phoenix.PubSub.unsubscribe(@pubsub, topic(room))
+  end
+
+  defp topic(%Room{id: room_id}), do: "chat_room:#{room_id}"
+
+  defp topic(room_id), do: topic(%Room{id: room_id})
 end

lib/slax_web/live/chat_room_live.ex

@@ -2,6 +2,8 @@ defmodule SlaxWeb.ChatRoomLive do
   @moduledoc false
   use SlaxWeb, :live_view
 
+  require Logger
+
   alias Slax.Accounts.User
   alias Slax.Chat
   alias Slax.Chat.Message
@@ -133,6 +135,8 @@ defmodule SlaxWeb.ChatRoomLive do
 
   @impl Phoenix.LiveView
   def handle_params(params, _session, socket) do
+    if socket.assigns[:room], do: Chat.unsubscribe_from_room(socket.assigns.room)
+
     room =
       case Map.fetch(params, "id") do
         {:ok, id} ->
@@ -144,6 +148,8 @@ defmodule SlaxWeb.ChatRoomLive do
 
     messages = Chat.list_messages_in_room(room)
 
+    Chat.subscribe_to_room(room)
+
     {:noreply,
      socket
      |> assign(hide_topic?: false, page_title: "# #{room.name}", room: room)
@@ -168,10 +174,8 @@ defmodule SlaxWeb.ChatRoomLive do
 
     socket =
       case Chat.create_message(room, user, message_params) do
-        {:ok, message} ->
-          socket
-          |> stream_insert(:messages, message)
-          |> assign_message_form(Chat.change_message(%Message{}))
+        {:ok, _message} ->
+          assign_message_form(socket, Chat.change_message(%Message{}))
 
         {:error, changeset} ->
           assign_message_form(socket, changeset)
@@ -182,8 +186,18 @@ defmodule SlaxWeb.ChatRoomLive do
 
   @impl Phoenix.LiveView
   def handle_event("delete-message", %{"id" => message_id}, socket) do
-    {:ok, message} = Chat.delete_message_by_id(message_id, socket.assigns.current_user)
+    Chat.delete_message_by_id(message_id, socket.assigns.current_user)
 
+    {:noreply, socket}
+  end
+
+  @impl Phoenix.LiveView
+  def handle_info({:new_message, message}, socket) do
+    {:noreply, stream_insert(socket, :messages, message)}
+  end
+
+  @impl Phoenix.LiveView
+  def handle_info({:deleted_message, message}, socket) do
     {:noreply, stream_delete(socket, :messages, message)}
   end