import 'package:flutter/foundation.dart';

/// ─────────────────────────────────────────────────────────────────────────
/// THE APP WITH NO BACKEND BEHIND IT
///
/// One switch that takes the whole app off the network: sign-in, the day's
/// work, and every status the rider writes. It exists so the flow can be built,
/// demonstrated and judged without `api.doormile.com` answering — on a bench, on
/// a plane, or against a backend that does not have the meal contract yet.
///
/// ── This app has been burned by a mock layer before ──
///
/// One was ripped out for a good reason: it wrote rows into the same
/// SharedPreferences stores the real work uses, so demo stops surfaced on live
/// riders' tabs weeks later with nothing left in the repo to explain them.
/// `purgeDemoRecords()` still runs at every launch to clean up after it.
///
/// Four rules keep this one from becoming that:
///
///  1. **It cannot ship.** [enabled] is false in a release build unless someone
///     types `--dart-define=MOCK_BACKEND=true` on the build command, which is
///     not something that happens by accident. Debug and profile builds — the
///     ones a developer actually runs — get it by default.
///  2. **It intercepts the transport, not the stores.** Everything is served as
///     an *API response*; nothing writes to a store that real work shares. The
///     app cannot tell the difference and neither can its data layer.
///  3. **Its ids are self-identifying.** Every record is `MOCK-…`, which is
///     exactly what `purgeDemoRecords()` looks for, so anything that does leak
///     into a store is removed at the next launch by code that already ships.
///  4. **It says so, loudly.** Every intercepted call is logged with a `[MOCK]`
///     prefix, so a confusing session is one glance at the console away from
///     being explained.
///
/// ── What is given up while it is on ──
///
/// The hub is not told anything. A rider can accept, arrive, pick up and
/// deliver, and the console will show none of it — every write is answered with
/// a success that was manufactured on the phone. That is the correct trade for
/// design and demo work and the wrong one for a real shift, which is what rule 1
/// is for.
/// ─────────────────────────────────────────────────────────────────────────

/// The one switch.
///
/// Default: **on** in debug and profile, **off** in release. Override either
/// way from the build command:
///
///     flutter run                                   # mock
///     flutter run --dart-define=MOCK_BACKEND=false  # real API
///     flutter build apk --dart-define=MOCK_BACKEND=true   # deliberate demo
/// ── Opt in, not opt out ──
///
/// This defaulted to **on** in debug and profile, so every `flutter run` served
/// a canned rider, a canned day and a canned login — and the backend was only
/// ever exercised by someone who remembered to turn the mock off. Three
/// consequences, all of which actually happened:
///
///  • A rider signing in with his real number became the fixture's rider.
///  • A whole class of contract bugs — a field renamed, a number sent where a
///    string was required — could not be seen, because nothing left the device.
///  • The default development experience diverged from production silently,
///    which is the one kind of divergence nobody notices until release.
///
/// The canned day is still one flag away, and is genuinely useful on a bench or
/// a plane. It is just no longer what you get by not deciding:
///
///     flutter run                                   # the real API
///     flutter run --dart-define=MOCK_BACKEND=true   # the canned day
const bool kMockBackend = bool.fromEnvironment('MOCK_BACKEND');

/// Canned answers for the routes the rider's day passes through.
///
/// Everything else gets a generic success, on purpose: the alternative is a
/// mock that fails on an endpoint nobody thought about and reads to the person
/// using it as a broken app rather than an unmapped route.
class MockBackend {
  MockBackend._();

  /// Whether the canned answers are being served.
  ///
  /// Settable so a test can exercise the transport itself — the interception
  /// happens *above* the HTTP client, so with this on there is no request to
  /// assert against. Nothing in the app assigns it; it follows [kMockBackend].
  static bool enabled = kMockBackend;

  /// The signed-in rider, when there is no server to ask.
  ///
  /// `tenantname` is what puts the build on the meal line — see
  /// [ServiceProfile] — so the mock day and the mock login agree about which
  /// application the rider is in.
  static const Map<String, dynamic> rider = {
    'userid': 90001,
    'id': 90001,
    'name': 'Suresh Kumar',
    'phone': '9876543210',
    'mobile': '9876543210',
    'email': 'suresh@doormile.test',
    'roleid': 5,
    'configid': 1001,
    'tenantid': 916,
    'tenantname': 'DailyGrubs',
    'status': 'Active',
    'vehicletype': 'Bike',
    'vehicleno': 'TN 37 CV 4412',
  };

  /// A token that is obviously not a JWT, so nothing tries to read claims out
  /// of it and no log line makes it look like a real session.
  static const String token = 'MOCK-TOKEN-not-a-real-session';

  /// Answers [method] [path], or null when the caller should fall through to
  /// the network. Null is never returned while [enabled] — see the class note.
  static Map<String, dynamic>? respond(
    String method,
    String path, {
    Object? body,
    Map<String, String>? query,
  }) {
    if (!enabled) return null;

    final route = path.split('?').first;
    debugPrint('[MOCK] $method $route');

    // ── Auth ──
    if (route.endsWith('/login')) {
      return _ok({'otpsent': true, 'phone': _field(body, 'phone')});
    }
    if (route.endsWith('/verify-pin')) {
      // The shape the real handler returns, verified against a live 200: the
      // profile lives under `user` / `user.profile`, and there is no `data`
      // key. Getting this wrong cost a debugging session once already — see the
      // note in [MilerApi].
      //
      // The phone is the one the rider actually typed. It used to be the
      // fixture's, so signing in with your own number made you Suresh Kumar and
      // the screen you landed on disagreed with the number on the screen you
      // came from — which reads as a broken login rather than as a mock.
      final phone = _field(body, 'phone');
      final signedIn = <String, dynamic>{
        ...rider,
        if (phone.isNotEmpty) ...{
          'phone': phone,
          'mobile': phone,
          'contactno': phone,
        },
      };
      return {
        'success': true,
        'message': 'ok',
        'token': token,
        'user': {...signedIn, 'profile': signedIn},
      };
    }
    if (route.endsWith('/profile')) return _ok(rider);

    // ── The day's work ──
    //
    // Empty rather than invented: the meal line's stops come from
    // [MealRunMock], which the provider reads *before* it reaches the network
    // at all. A parcel booking list has no fixture and inventing one here would
    // put fictional consignments in front of a parcel rider.
    if (route.endsWith('/bookings') || route.endsWith('/assignments')) {
      return _ok(const <dynamic>[]);
    }

    // ── Everything the rider writes ──
    //
    // Accept, reject, reached, parcels, payment, pickup-complete, deliver,
    // skip, duty, breaks, telemetry, device tokens. All answered yes, and all
    // going nowhere.
    return _ok(const <String, dynamic>{});
  }

  static Map<String, dynamic> _ok(dynamic data) => {
    'success': true,
    'message': 'ok',
    'data': data,
  };

  static String _field(Object? body, String key) =>
      (body is Map && body[key] != null) ? body[key].toString() : '';
}