Fix stale PubSub subscriptions on record navigation

Subscription management was only done in mount/3, meaning
navigating to a different record via handle_params/3 left the
old subscription active. A background update for the old record
would then overwrite the currently displayed record.

Fix: manage subscriptions in handle_params/3 (unsubscribe old,
subscribe new) via shared RecordActions.manage_subscription/2,
and guard handle_info({:update,...}) against mismatched IDs.

lib/music_library/records.ex

@@ -110,6 +110,14 @@ defmodule MusicLibrary.Records do
     Phoenix.PubSub.subscribe(MusicLibrary.PubSub, "records:#{record_id}")
   end
 
+  @doc """
+  Unsubscribes the calling process from updates for a given record.
+  """
+  @spec unsubscribe(String.t()) :: :ok | {:error, term()}
+  def unsubscribe(record_id) do
+    Phoenix.PubSub.unsubscribe(MusicLibrary.PubSub, "records:#{record_id}")
+  end
+
   @spec notify_update(Record.t()) :: :ok | {:error, term()}
   def notify_update(record) do
     Phoenix.PubSub.broadcast(

lib/music_library_web/live/collection_live/show.ex

@@ -348,11 +348,7 @@ defmodule MusicLibraryWeb.CollectionLive.Show do
   end
 
   @impl true
-  def mount(%{"id" => record_id}, _session, socket) do
-    if connected?(socket) do
-      Records.subscribe(record_id)
-    end
-
+  def mount(_params, _session, socket) do
     {:ok,
      socket
      |> assign(:current_section, :collection)
@@ -362,6 +358,8 @@ defmodule MusicLibraryWeb.CollectionLive.Show do
 
   @impl true
   def handle_params(%{"id" => id}, _, socket) do
+    RecordActions.manage_subscription(socket, id)
+
     record = Records.get_record!(id)
     last_listened_track = ListeningStats.get_last_listened_track(record)
     play_count = ListeningStats.play_count(record)
@@ -474,10 +472,14 @@ defmodule MusicLibraryWeb.CollectionLive.Show do
 
   @impl true
   def handle_info({:update, record}, socket) do
+    if record.id == socket.assigns.record.id do
       {:noreply,
        socket
        |> RecordActions.handle_record_updated(record)
        |> assign_similar_records()}
+    else
+      {:noreply, socket}
+    end
   end
 
   defp page_title(action, record) do

lib/music_library_web/live/wishlist_live/show.ex

@@ -284,13 +284,9 @@ defmodule MusicLibraryWeb.WishlistLive.Show do
   end
 
   @impl true
-  def mount(%{"id" => record_id}, _session, socket) do
+  def mount(_params, _session, socket) do
     current_date = DateTime.utc_now() |> DateTime.to_date()
 
-    if connected?(socket) do
-      Records.subscribe(record_id)
-    end
-
     {:ok,
      socket
      |> assign(current_section: :wishlist)
@@ -299,6 +295,8 @@ defmodule MusicLibraryWeb.WishlistLive.Show do
 
   @impl true
   def handle_params(%{"id" => id}, _, socket) do
+    RecordActions.manage_subscription(socket, id)
+
     record = Records.get_record!(id)
     online_store_templates = OnlineStoreTemplates.list_enabled_templates()
 
@@ -367,7 +365,11 @@ defmodule MusicLibraryWeb.WishlistLive.Show do
 
   @impl true
   def handle_info({:update, record}, socket) do
+    if record.id == socket.assigns.record.id do
       {:noreply, RecordActions.handle_record_updated(socket, record)}
+    else
+      {:noreply, socket}
+    end
   end
 
   defp page_title(action, record) do

lib/music_library_web/live_helpers/record_actions.ex

@@ -97,6 +97,20 @@ defmodule MusicLibraryWeb.LiveHelpers.RecordActions do
     end
   end
 
+  @doc """
+  Manages PubSub subscriptions when navigating between records.
+  Unsubscribes from the previous record (if any) and subscribes to the new one,
+  but only when the socket is connected.
+  """
+  def manage_subscription(socket, new_id) do
+    if Phoenix.LiveView.connected?(socket) do
+      if socket.assigns[:record], do: Records.unsubscribe(socket.assigns.record.id)
+      Records.subscribe(new_id)
+    end
+
+    :ok
+  end
+
   def handle_chats_changed(socket) do
     {:noreply,
      assign(socket, :chat_count, Chats.count_chats(:record, socket.assigns.record.musicbrainz_id))}