Ensure uniqueness of scrobble rules

lib/music_library/scrobble_rules/scrobble_rule.ex

@@ -29,5 +29,6 @@ defmodule MusicLibrary.ScrobbleRules.ScrobbleRule do
     scrobble_rule
     |> cast(attrs, [:type, :match_value, :target_musicbrainz_id, :enabled, :description])
     |> validate_required([:type, :match_value, :target_musicbrainz_id])
+    |> unique_constraint([:type, :match_value], error_key: :match_value)
   end
 end

priv/repo/migrations/20260202101204_add_scrobble_rules_constraints.exs

@@ -0,0 +1,8 @@
+defmodule MusicLibrary.Repo.Migrations.AddScrobbleRulesConstraints do
+  use Ecto.Migration
+
+  def change do
+    drop index(:scrobble_rules, [:type, :match_value])
+    create unique_index(:scrobble_rules, [:type, :match_value], unique: true)
+  end
+end

test/music_library/scrobble_rules_test.exs

@@ -95,6 +95,17 @@ defmodule MusicLibrary.ScrobbleRulesTest do
       assert scrobble_rule.description == "Fix Pink Floyd album"
     end
 
+    test "create_scrobble_rule/1 doesn't allow duplicates for the same type" do
+      valid_attrs = Map.put(@valid_album_attrs, :type, :album)
+
+      assert {:ok, %ScrobbleRule{} = scrobble_rule} =
+               ScrobbleRules.create_scrobble_rule(valid_attrs)
+
+      assert scrobble_rule.type == :album
+
+      assert {:error, _changeset} = ScrobbleRules.create_scrobble_rule(valid_attrs)
+    end
+
     test "create_scrobble_rule/1 with invalid data returns error changeset" do
       assert {:error, %Ecto.Changeset{}} = ScrobbleRules.create_scrobble_rule(@invalid_attrs)
     end