// Version: 1.0.0 | Created: 2026-07-04
// Verifies the chat timeline requests older history when scrolled near the
// top (oldest end) of the reverse list. Driven through the real widget tree
// with a fake repository, since Playwright cannot scroll the CanvasKit surface.

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:matrix/matrix.dart';

import 'package:m8chat_app/core/network/matrix_client.dart';
import 'package:m8chat_app/features/chat/data/chat_repository.dart';
import 'package:m8chat_app/features/chat/domain/message_model.dart';
import 'package:m8chat_app/features/chat/presentation/chat_controller.dart';
import 'package:m8chat_app/features/chat/presentation/chat_screen.dart';

class _FakeChatRepository extends ChatRepository {
  _FakeChatRepository() : super(client: Client('test-client'));

  int loadMoreCalls = 0;
  bool _hasMore = true;

  @override
  bool canLoadMore(String roomId) => _hasMore;

  @override
  Future<void> loadMoreMessages(String roomId) async {
    loadMoreCalls++;
    _hasMore = false; // one page then exhausted
  }
}

void main() {
  testWidgets('scrolling to the top requests older history once', (
    tester,
  ) async {
    const roomId = '!paginate:server';
    final base = DateTime(2026, 7, 4, 8);
    final messages = [
      for (var i = 40; i >= 1; i--)
        MessageModel(
          eventId: '\$e$i',
          roomId: roomId,
          senderId: '@me:server',
          senderDisplayName: 'Me',
          timestamp: base.add(Duration(seconds: i)),
          type: MessageType.text,
          body: 'Message $i',
          isMine: true,
        ),
    ];

    final repo = _FakeChatRepository();

    await tester.pumpWidget(
      ProviderScope(
        overrides: [
          matrixClientProvider.overrideWithValue(Client('test-client')),
          chatRepositoryProvider.overrideWithValue(repo),
          chatTimelineProvider(
            roomId,
          ).overrideWith((ref) => Stream.value(messages)),
        ],
        child: const MaterialApp(home: ChatScreen(roomId: roomId)),
      ),
    );
    await tester.pumpAndSettle();

    expect(repo.loadMoreCalls, 0);

    // Confirm the override is actually in effect.
    final container = ProviderScope.containerOf(
      tester.element(find.byType(ChatScreen)),
    );
    expect(identical(container.read(chatRepositoryProvider), repo), isTrue);

    double offset() => tester
        .state<ScrollableState>(find.byType(Scrollable).first)
        .position
        .pixels;
    double maxExtent() => tester
        .state<ScrollableState>(find.byType(Scrollable).first)
        .position
        .maxScrollExtent;

    // Scroll up toward the oldest end (reverse list: drag content down).
    await tester.drag(find.byType(ListView), const Offset(0, 3000));
    await tester.pumpAndSettle();

    expect(
      offset(),
      greaterThan(maxExtent() - 400),
      reason:
          'drag should have reached the oldest end (offset=${offset()}, '
          'max=${maxExtent()})',
    );

    expect(
      repo.loadMoreCalls,
      greaterThan(0),
      reason: 'reaching the top should request older history',
    );
  });
}