Use Ecto.UUID instead of hand-rolled type

lib/music_library/scrobble_rules/scrobble_rule.ex

@@ -19,7 +19,7 @@ defmodule MusicLibrary.ScrobbleRules.ScrobbleRule do
   schema "scrobble_rules" do
     field :type, :string
     field :match_value, :string
-    field :target_musicbrainz_id, :string
+    field :target_musicbrainz_id, Ecto.UUID
     field :enabled, :boolean, default: true
     field :description, :string
 
@@ -32,28 +32,5 @@ defmodule MusicLibrary.ScrobbleRules.ScrobbleRule do
     |> cast(attrs, [:type, :match_value, :target_musicbrainz_id, :enabled, :description])
     |> validate_required([:type, :match_value, :target_musicbrainz_id])
     |> validate_inclusion(:type, @valid_types)
-    |> validate_musicbrainz_id_format(:target_musicbrainz_id)
-  end
-
-  defp validate_musicbrainz_id_format(changeset, field) do
-    validate_change(changeset, field, fn _, value ->
-      case value do
-        "" ->
-          [{field, "cannot be empty"}]
-
-        value when is_binary(value) ->
-          if String.match?(
-               value,
-               ~r/^[a-f0-9]{8}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{12}$/i
-             ) do
-            []
-          else
-            [{field, "must be a valid MusicBrainz ID (UUID format)"}]
-          end
-
-        _ ->
-          [{field, "must be a string"}]
-      end
-    end)
   end
 end

test/music_library/scrobble_rules/scrobble_rule_test.exs

@@ -108,7 +108,7 @@ defmodule MusicLibrary.ScrobbleRules.ScrobbleRuleTest do
       changeset = ScrobbleRule.changeset(%ScrobbleRule{}, attrs)
       refute changeset.valid?
 
-      assert "must be a valid MusicBrainz ID (UUID format)" in errors_on(changeset).target_musicbrainz_id
+      assert "is invalid" in errors_on(changeset).target_musicbrainz_id
     end
 
     test "valid changeset with uppercase UUID" do

test/music_library_web/live/scrobble_rules_live_test.exs

@@ -162,7 +162,7 @@ defmodule MusicLibraryWeb.ScrobbleRulesLiveTest do
                  target_musicbrainz_id: "invalid-uuid"
                }
              )
-             |> render_change() =~ "must be a valid MusicBrainz ID"
+             |> render_change() =~ "is invalid"
     end
 
     test "updates form labels based on rule type", %{conn: conn} do