frosty/lib/widgets/follow_channel_controller.dart

import 'package:frosty/apis/base_api_client.dart';
import 'package:frosty/apis/twitch_integrity.dart';
import 'package:frosty/screens/settings/stores/auth_store.dart';

/// Shared follow/unfollow state + GQL mutations for channel UI.
///
/// Owns loading/action flags and the session cache via [AuthStore.user].
/// Callers handle UI (integrity WebView, login prompt, snackbars).
class FollowChannelController {
  final AuthStore authStore;
  final String userId;
  final bool? initialIsFollowing;
  final void Function() onChanged;

  bool? isFollowing;
  bool loading = false;
  bool actionInProgress = false;

  FollowChannelController({
    required this.authStore,
    required this.userId,
    this.initialIsFollowing,
    required this.onChanged,
  });

  bool get isSelf =>
      authStore.user.details?.id != null &&
      authStore.user.details!.id == userId;

  bool get canFollow => authStore.isLoggedIn && !isSelf;

  /// Whether the follow control should be visible (loading or known state).
  bool get shouldShow => canFollow && (loading || isFollowing != null);

  void init() {
    if (!canFollow) return;
    if (initialIsFollowing != null) {
      isFollowing = initialIsFollowing;
      onChanged();
      return;
    }
    loadFollowState();
  }

  Future<void> loadFollowState() async {
    final cached = authStore.user.cachedIsFollowing(userId);
    if (cached != null) {
      isFollowing = cached;
      onChanged();
      return;
    }

    loading = true;
    onChanged();
    try {
      final following = await authStore.user.isFollowingChannel(userId);
      isFollowing = following;
    } catch (_) {
      // Leave isFollowing null so the control stays hidden.
    } finally {
      loading = false;
      onChanged();
    }
  }

  /// Toggles follow. Returns the new following state on success.
  ///
  /// Throws [IntegrityCheckException] when a WebView integrity mint is needed,
  /// [ApiException] for API errors, or [StateError] when not ready / no token.
  Future<bool> toggle() async {
    if (actionInProgress || isFollowing == null) {
      throw StateError('Follow toggle not ready');
    }

    final gqlToken = authStore.gqlToken;
    if (gqlToken == null) {
      throw const FollowNeedsWebSessionException();
    }

    final following = isFollowing!;
    actionInProgress = true;
    onChanged();

    try {
      await _runMutation(following: following, gqlToken: gqlToken);
    } catch (_) {
      actionInProgress = false;
      onChanged();
      rethrow;
    }

    final nowFollowing = !following;
    isFollowing = nowFollowing;
    actionInProgress = false;
    onChanged();
    return nowFollowing;
  }

  /// After a WebView integrity mint, apply credentials and retry [toggle]'s
  /// intended mutation (still based on the pre-toggle [wasFollowing] state).
  Future<bool> retryAfterIntegrity({
    required bool wasFollowing,
    required GqlIntegrityCredentials credentials,
  }) async {
    final gqlToken = authStore.gqlToken;
    if (gqlToken == null) {
      throw const FollowNeedsWebSessionException();
    }

    actionInProgress = true;
    onChanged();

    try {
      await authStore.user.applyWebIntegrity(credentials);
      await _runMutation(following: wasFollowing, gqlToken: gqlToken);
    } catch (_) {
      actionInProgress = false;
      onChanged();
      rethrow;
    }

    final nowFollowing = !wasFollowing;
    isFollowing = nowFollowing;
    actionInProgress = false;
    onChanged();
    return nowFollowing;
  }

  Future<void> _runMutation({
    required bool following,
    required String gqlToken,
  }) async {
    if (following) {
      await authStore.user.unfollow(targetId: userId, gqlToken: gqlToken);
    } else {
      await authStore.user.follow(targetId: userId, gqlToken: gqlToken);
    }
  }

  void clearActionInProgress() {
    if (!actionInProgress) return;
    actionInProgress = false;
    onChanged();
  }
}

/// Thrown when follow needs a linked Twitch web (GQL) session.
class FollowNeedsWebSessionException implements Exception {
  const FollowNeedsWebSessionException();
}