import 'dart:async';

import 'package:clock/clock.dart';
import 'package:fake_async/fake_async.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:halkyon_app/halkyon_app.dart';
import 'package:halkyon_app/testing.dart';

void main() {
  TestWidgetsFlutterBinding.ensureInitialized();

  late int syncs;
  late Exception? failWith;
  late VoidCallback? merge;
  // While set and not completed, a sync keeps running.
  late Completer<void>? hold;

  SyncService service({
    PendingChangesStore? pendingChanges,
    bool syncedBefore = false,
  }) => SyncService(
    ({required onMerge}) async {
      syncs++;
      merge = onMerge;
      await hold?.future;
      if (failWith case final error?) {
        throw error;
      }
    },
    pendingChanges: pendingChanges,
    syncedBefore: syncedBefore,
  );

  setUp(() {
    syncs = 0;
    failWith = null;
    merge = null;
    hold = null;
  });

  test('syncs once at start', () {
    fakeAsync((async) {
      final sync = service()..start();
      async.flushMicrotasks();

      expect(syncs, 1);
      sync.dispose();
    });
  });

  test('syncs once after a burst of local changes has settled', () {
    fakeAsync((async) {
      final sync = service()..start();
      async.flushMicrotasks();

      sync
        ..requestSync()
        ..requestSync();
      async.elapse(const Duration(seconds: 1));
      sync.requestSync();
      async.elapse(const Duration(seconds: 1));
      expect(syncs, 1, reason: 'still within the debounce');

      async.elapse(const Duration(seconds: 1));
      expect(syncs, 2);
      sync.dispose();
    });
  });

  test('syncs every five minutes without other triggers', () {
    fakeAsync((async) {
      final sync = service()..start();
      async.elapse(const Duration(minutes: 10));

      expect(syncs, 3);
      sync.dispose();
    });
  });

  test('keeps syncing after a failed sync', () {
    fakeAsync((async) {
      failWith = Exception('No connection');
      final sync = service()..start();
      async.flushMicrotasks();

      failWith = null;
      sync.requestSync();
      async.elapse(const Duration(seconds: 2));

      expect(syncs, 2);
      sync.dispose();
    });
  });

  test('reports changes from other devices', () {
    fakeAsync((async) {
      final sync = service();
      var merges = 0;
      sync.merges.listen((_) => merges++);
      sync.start();
      async.flushMicrotasks();

      merge!();
      async.flushMicrotasks();

      expect(merges, 1);
      sync.dispose();
    });
  });

  test('a trigger during a sync runs one more sync afterwards', () {
    fakeAsync((async) {
      final running = hold = Completer<void>();
      final sync = service()..start();
      async.flushMicrotasks();

      sync.requestSync();
      async.elapse(const Duration(seconds: 2));
      sync.requestSync();
      async.elapse(const Duration(seconds: 2));
      expect(syncs, 1, reason: 'the first sync is still running');

      running.complete();
      async.flushMicrotasks();
      expect(syncs, 2);
      sync.dispose();
    });
  });

  test('lets a running sync finish before it stops', () {
    fakeAsync((async) {
      final running = hold = Completer<void>();
      final sync = service()..start();
      async.flushMicrotasks();
      sync.requestSync();
      async.elapse(const Duration(seconds: 2));

      var stopped = false;
      unawaited(sync.dispose().then((_) => stopped = true));
      async.flushMicrotasks();
      expect(stopped, isFalse, reason: 'the database is still in use');

      running.complete();
      async.flushMicrotasks();
      expect(stopped, isTrue);
      expect(syncs, 1, reason: 'no sync starts once it is stopping');
    });
  });

  test('stops syncing when disposed', () {
    fakeAsync((async) {
      final sync = service()..start();
      async.flushMicrotasks();
      sync
        ..requestSync()
        ..dispose();

      async.elapse(const Duration(minutes: 10));
      expect(syncs, 1);
    });
  });

  group('status', () {
    final noon = DateTime.utc(2026, 10, 3, 12);

    test('nothing has synced before the first sync', () {
      expect(service().status, const SyncStatus());
      expect(service().status.hasTrouble, isFalse);
    });

    test('says while a sync runs, and when it went through', () {
      fakeAsync((async) {
        withClock(async.getClock(noon), () {
          final running = hold = Completer<void>();
          final sync = service()..start();
          async.flushMicrotasks();
          expect(sync.status, const SyncStatus(syncing: true));

          async.elapse(const Duration(seconds: 3));
          running.complete();
          async.flushMicrotasks();
          expect(
            sync.status,
            SyncStatus(
              lastSyncedAt: noon.add(const Duration(seconds: 3)),
              syncedHere: true,
            ),
          );
          sync.dispose();
        });
      });
    });

    test('a failed sync is trouble until a sync goes through again', () {
      fakeAsync((async) {
        withClock(async.getClock(noon), () {
          final sync = service()..start();
          async.flushMicrotasks();

          failWith = Exception('No connection');
          async.elapse(const Duration(minutes: 5));
          expect(
            sync.status,
            SyncStatus(
              lastSyncedAt: noon,
              failure: (
                at: noon.add(const Duration(minutes: 5)),
                appMismatch: false,
              ),
              syncedHere: true,
            ),
          );
          expect(sync.status.hasTrouble, isTrue);

          failWith = null;
          async.elapse(const Duration(minutes: 5));
          expect(
            sync.status,
            SyncStatus(
              lastSyncedAt: noon.add(const Duration(minutes: 10)),
              syncedHere: true,
            ),
          );
          sync.dispose();
        });
      });
    });

    test('still shows the failure while the next sync runs', () {
      fakeAsync((async) {
        withClock(async.getClock(noon), () {
          failWith = Exception('No connection');
          final sync = service()..start();
          async.flushMicrotasks();

          hold = Completer<void>();
          sync.syncNow();
          async.flushMicrotasks();
          expect(sync.status.syncing, isTrue);
          expect(sync.status.hasTrouble, isTrue);
          hold!.complete();
          sync.dispose();
        });
      });
    });

    test("tells when this app and the server don't match", () {
      fakeAsync((async) {
        withClock(async.getClock(noon), () {
          failWith = const AppServerMismatchException();
          final sync = service()..start();
          async.flushMicrotasks();

          expect(sync.status.appMismatch, isTrue);
          expect(sync.status.failure, (at: noon, appMismatch: true));
          sync.dispose();
        });
      });
    });

    test('reports every change', () {
      fakeAsync((async) {
        final sync = service();
        final seen = <SyncStatus>[];
        sync.statusChanges.listen(seen.add);
        sync.start();
        async.flushMicrotasks();

        expect(seen.map((status) => status.syncing), [true, false]);
        sync.dispose();
      });
    });
  });

  test('syncs at once when the person asks', () {
    fakeAsync((async) {
      final sync = service()..start();
      async.flushMicrotasks();

      sync.syncNow();
      async.flushMicrotasks();

      expect(syncs, 2, reason: 'no waiting for changes to settle');
      sync.dispose();
    });
  });

  group('changes not on the server yet', () {
    test('are the saves since the last sync that went through', () {
      fakeAsync((async) {
        final sync = service()..start();
        async.flushMicrotasks();

        sync
          ..requestSync()
          ..requestSync();
        expect(sync.status.pending, 2);

        async.elapse(const Duration(seconds: 2));
        expect(sync.status.pending, 0);
        sync.dispose();
      });
    });

    test('stay while syncs fail', () {
      fakeAsync((async) {
        failWith = Exception('No connection');
        final sync = service()..start();
        async.flushMicrotasks();

        sync.requestSync();
        async.elapse(const Duration(seconds: 2));
        expect(sync.status.pending, 1);
        expect(sync.status.hasTrouble, isTrue);

        failWith = null;
        sync.syncNow();
        async.flushMicrotasks();
        expect(sync.status.pending, 0);
        sync.dispose();
      });
    });

    test('saved while a sync runs, wait for the next', () {
      fakeAsync((async) {
        final running = hold = Completer<void>();
        final sync = service()..start();
        async.flushMicrotasks();

        sync.requestSync();
        running.complete();
        async.flushMicrotasks();
        expect(sync.status.pending, 1);

        hold = null;
        async.elapse(const Duration(seconds: 2));
        expect(sync.status.pending, 0);
        sync.dispose();
      });
    });

    test('are kept while the app is closed, and taken by the first sync', () {
      fakeAsync((async) {
        failWith = Exception('No connection');
        final kept = MemoryPendingChangesStore(3);
        final sync = service(pendingChanges: kept)..start();
        async.flushMicrotasks();
        expect(sync.status.pending, 3);

        sync.requestSync();
        async.flushMicrotasks();
        expect(kept.kept, 4);

        failWith = null;
        sync.syncNow();
        async.flushMicrotasks();
        expect(sync.status.pending, 0);
        expect(kept.kept, 0);
        sync.dispose();
      });
    });
  });

  test('says whether a sync ever went through on this device: as kept from '
      'before, and from the first that goes through, kept for next '
      'time', () {
    fakeAsync((async) {
      expect(service(syncedBefore: true).status.syncedHere, isTrue);

      failWith = Exception('No connection');
      final kept = MemoryPendingChangesStore(0, false);
      final sync = service(pendingChanges: kept)..start();
      async.flushMicrotasks();
      expect(sync.status.syncedHere, isFalse);
      expect(sync.status.hasTrouble, isTrue);

      failWith = null;
      sync.syncNow();
      async.flushMicrotasks();
      expect(sync.status.syncedHere, isTrue);
      expect(kept.synced, isTrue);

      sync.requestSync();
      async.flushMicrotasks();
      expect(sync.status.syncedHere, isTrue);
      sync.dispose();
    });
  });
}