import 'package:flutter_test/flutter_test.dart';
import 'package:fuel_tax_tracker/services/merge_utils.dart';

class _Record {
  final String id;
  final String value;
  final DateTime updatedAt;

  _Record(this.id, this.value, this.updatedAt);
}

void main() {
  group('mergeById', () {
    test('unions records that only exist on one side', () {
      final remote = [_Record('a', 'remote-a', DateTime(2024, 1, 1))];
      final local = [_Record('b', 'local-b', DateTime(2024, 1, 1))];

      final result = mergeById(remote, local, (r) => r.id, (r) => r.updatedAt);

      expect(result.map((r) => r.id), containsAll(['a', 'b']));
      expect(result.length, 2);
    });

    test('keeps the newer updatedAt when a record exists on both sides', () {
      final remote = [_Record('a', 'remote-old', DateTime(2024, 1, 1))];
      final local = [_Record('a', 'local-new', DateTime(2024, 6, 1))];

      final result = mergeById(remote, local, (r) => r.id, (r) => r.updatedAt);

      expect(result.length, 1);
      expect(result.first.value, 'local-new');
    });

    test('keeps the remote copy when it is newer than local', () {
      final remote = [_Record('a', 'remote-new', DateTime(2024, 6, 1))];
      final local = [_Record('a', 'local-old', DateTime(2024, 1, 1))];

      final result = mergeById(remote, local, (r) => r.id, (r) => r.updatedAt);

      expect(result.length, 1);
      expect(result.first.value, 'remote-new');
    });

    test('local wins ties', () {
      final sameTime = DateTime(2024, 1, 1);
      final remote = [_Record('a', 'remote', sameTime)];
      final local = [_Record('a', 'local', sameTime)];

      final result = mergeById(remote, local, (r) => r.id, (r) => r.updatedAt);

      expect(result.first.value, 'local');
    });
  });
}