feat(leaderboard_repository): enable ability to check if a username is allowed

packages/leaderboard_repository/lib/src/leaderboard_repository.dart

@@ -152,4 +152,15 @@ class LeaderboardRepository {
       throw FetchPlayerRankingException(error, stackTrace);
     }
   }
+
+  /// Checks if the given [username] is allowed. The [username] is not allowed
+  /// if it is a bad word.
+  Future<bool> isUsernameAllowed({required String username}) async {
+    // TODO(jonathandaniels-vgv): load this list of bad words from an endpoint
+    final badWords = <String>['badword'];
+    final filteredUsername = username.trim().toLowerCase();
+    final isUsernameABadWord = badWords.contains(filteredUsername);
+    final isUsernameAllowed = !isUsernameABadWord;
+    return isUsernameAllowed;
+  }
 }

packages/leaderboard_repository/test/src/leaderboard_repository_test.dart

@@ -223,5 +223,46 @@ void main() {
         );
       });
     });
+
+    group('isUsernameAllowed', () {
+      late LeaderboardRepository leaderboardRepository;
+
+      setUp(() async {
+        leaderboardRepository = LeaderboardRepository(firestore);
+      });
+
+      test('returns true if username is not a bad word', () async {
+        final isUsernameAllowedResponse =
+            await leaderboardRepository.isUsernameAllowed(
+          username: 'goodword',
+        );
+        expect(
+          isUsernameAllowedResponse,
+          isTrue,
+        );
+      });
+
+      test('returns false if username is a bad word', () async {
+        final isUsernameAllowedResponse =
+            await leaderboardRepository.isUsernameAllowed(
+          username: 'badword',
+        );
+        expect(
+          isUsernameAllowedResponse,
+          isFalse,
+        );
+      });
+
+      test('bad word detection should be case insensitive', () async {
+        final isUsernameAllowedResponse =
+            await leaderboardRepository.isUsernameAllowed(
+          username: '  bAdWoRd  ',
+        );
+        expect(
+          isUsernameAllowedResponse,
+          isFalse,
+        );
+      });
+    });
   });
 }