import 'dart:async';

import 'package:equatable/equatable.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:halkyon_app/src/auth/data/auth_repository.dart';
import 'package:halkyon_app/src/auth/model/auth_status.dart';
import 'package:halkyon_app/src/auth/model/github_sign_in.dart';

/// Keeps a person signed in: follows who is signed in, and signs out on
/// request. Nobody signed in (at a first start, after signing out or
/// deleting the account, or once the server ended the session), it asks
/// how to start: every account has a way in, and nothing is made until the
/// person chooses (ADR 0020, D4). An anonymous account's session left from
/// before they went ends as the app starts, the account deleted (D25).
class SessionBloc(final AuthRepository _auth)
    extends Bloc<SessionEvent, SessionState> {
  this : super(const SessionStateLoading()) {
    on<SessionEventStarted>(_onStarted);
    on<SessionEventGitHubRequested>(_onGitHubRequested);
    on<SessionEventPasswordOfferDone>(
      (event, emit) => emit(_stateOf(_auth.status)),
    );
    on<SessionEventSignedOut>(
      (event, emit) => emit(SessionStateSignedOut(problem: event.problem)),
    );
    on<SessionEventSignOutRequested>(_onSignOutRequested);
    on<SessionEventDeleteRequested>(_onDeleteRequested);
  }

  Future<void> _onStarted(
    SessionEventStarted event,
    Emitter<SessionState> emit,
  ) async {
    if (_auth.isAnonymous) {
      try {
        await _auth.endAnonymousSession();
      } on Object catch (error, st) {
        // Only the device's own storage fails it: the session stays, but
        // nothing works in it any more ([_stateOf]).
        addError(error, st);
      }
    }
    emit(_stateOf(_auth.status));
    await emit.forEach<AuthStatus>(_auth.statusChanges, onData: _stateOf);
  }

  /// Signing in with GitHub: the GitHub account's person, if there is one.
  Future<void> _onGitHubRequested(
    SessionEventGitHubRequested event,
    Emitter<SessionState> emit,
  ) async {
    emit(const SessionStateSignedOut(busy: true));
    // The person signed in with GitHub is offered a password first (ADR
    // 0017, D2: "at their next sign-in"), while that sign-in is recent
    // enough for the instance to take one (the fourth reading).
    _offerPassword = true;
    try {
      if (!await _auth.switchToGitHub()) {
        _offerPassword = false;
        emit(const SessionStateSignedOut());
      }
      // Signed in: the status change shows the offer, then the person's
      // app.
    } on GitHubSignInFailed catch (e) {
      _offerPassword = false;
      emit(
        SessionStateSignedOut(
          problem: switch (e.problem) {
            GitHubSignInProblem.unknownAccount =>
              SignedOutProblem.noGitHubAccount,
            GitHubSignInProblem.usePassword => SignedOutProblem.usePassword,
            GitHubSignInProblem.ended => SignedOutProblem.gitHubEnded,
            GitHubSignInProblem.deprecated ||
            GitHubSignInProblem.refused => SignedOutProblem.failed,
          },
        ),
      );
    } on Object catch (error, st) {
      _offerPassword = false;
      addError(error, st);
      emit(const SessionStateSignedOut(problem: SignedOutProblem.failed));
    }
  }

  /// Whether the next person signed in comes from a GitHub sign-in, and is
  /// offered a password before their app ([SessionStateGitHubSignedIn]).
  bool _offerPassword = false;

  Future<void> _onSignOutRequested(
    SessionEventSignOutRequested event,
    Emitter<SessionState> emit,
  ) => _onAccountAction(
    SessionAction.signOut,
    // The instance out of reach signs out on this device all the same
    // (Serverpod's `signOutDevice`), as signing out of a borrowed device
    // must work offline; only the device's own storage fails it.
    _auth.signOut,
    SessionProblem.signOutFailed,
    emit,
  );

  Future<void> _onDeleteRequested(
    SessionEventDeleteRequested event,
    Emitter<SessionState> emit,
  ) => _onAccountAction(
    SessionAction.delete,
    _auth.deleteAccount,
    SessionProblem.deleteFailed,
    emit,
  );

  /// Runs [action] for the signed-in person's account, their app in place
  /// meanwhile, [busy] saying what is under way: never through the launch
  /// screen ([SessionStateLoading]), which would close the app and, should
  /// [action] fail, open it again with no word of why. Done, the status
  /// change to signed out asks how to start; failed, the person stays,
  /// told so by [problem].
  Future<void> _onAccountAction(
    SessionAction busy,
    Future<void> Function() action,
    SessionProblem problem,
    Emitter<SessionState> emit,
  ) async {
    if (_auth.status case final SignedIn person) {
      emit(SessionStateActive(person, busy: busy));
    }
    try {
      await action();
    } on Object catch (error, st) {
      addError(error, st);
      emit(switch (_auth.status) {
        final SignedIn person => SessionStateActive(person, problem: problem),
        SignedOut() => const SessionStateSignedOut(),
      });
    }
  }

  SessionState _stateOf(AuthStatus status) => switch (status) {
    // Nothing works in an anonymous account any more (D25): only one that
    // began before the app started could be signed in, and it has ended.
    SignedIn(isIdentified: false) => const SessionStateSignedOut(),
    SignedIn() when _offerPassword => _offered(status),
    SignedIn() => SessionStateActive(status),
    SignedOut() => const SessionStateSignedOut(),
  };

  SessionState _offered(SignedIn person) {
    _offerPassword = false;
    return SessionStateGitHubSignedIn(person);
  }
}

/// What happens to the session.
sealed class const SessionEvent() with Equatable {
  @override
  List<Object?> get props => const [];
}

/// The app starts: follow who is signed in, and end an anonymous account's
/// session left from before (ADR 0020, D25).
final class const SessionEventStarted() extends SessionEvent;

/// Sign in with GitHub, once signed out.
final class const SessionEventGitHubRequested() extends SessionEvent;

/// Signed out, [problem] if any saying why the last way to start failed.
final class const SessionEventSignedOut({final SignedOutProblem? problem})
    extends SessionEvent {
  @override
  List<Object?> get props => [problem];
}

/// The password offered after a GitHub sign-in was set up, put off, or not
/// needed: on to the person's app.
final class const SessionEventPasswordOfferDone() extends SessionEvent;

/// The person confirmed that they want to sign out.
final class const SessionEventSignOutRequested() extends SessionEvent;

/// Delete the signed-in person with everything they have; the person has
/// confirmed it.
final class const SessionEventDeleteRequested() extends SessionEvent;

/// Whether the app has a signed-in person to work for.
sealed class const SessionState() with Equatable;

/// Finding out who is signed in.
final class const SessionStateLoading() extends SessionState {
  @override
  List<Object?> get props => const [];
}

/// A person is signed in.
final class const SessionStateActive(
  /// Who is signed in.
  final SignedIn person, {

  /// What is under way for the account (signing out, deleting it), while
  /// the person's app stays; null for nothing.
  final SessionAction? busy,

  /// Why the last of those failed, the person still signed in; null for
  /// none.
  final SessionProblem? problem,
}) extends SessionState {
  @override
  List<Object?> get props => [person, busy, problem];
}

/// What the person asked for their account, under way while their app
/// stays.
enum SessionAction() {
  /// Signing out.
  signOut,

  /// Deleting the account.
  delete,
}

/// Why signing out or deleting the account failed, the person still signed
/// in.
enum SessionProblem() {
  /// Signing out failed on this device: the instance not reached signs out
  /// here all the same, so only the device's own storage fails it.
  signOutFailed,

  /// Deleting the account failed, the instance not reached or refusing:
  /// nothing deleted.
  deleteFailed,
}

/// [person] signed in with GitHub just now: before their app, a password
/// is offered where the instance offers one and they have none (ADR 0017,
/// D2), while the sign-in is recent enough to set it.
final class const SessionStateGitHubSignedIn(
  /// Who signed in.
  final SignedIn person,
) extends SessionState {
  @override
  List<Object?> get props => [person];
}

/// Nobody is signed in: the app asks how to start.
final class const SessionStateSignedOut({
  /// Whether a way to start is under way.
  final bool busy = false,

  /// Why the last way to start failed; null for none.
  final SignedOutProblem? problem,
}) extends SessionState {
  @override
  List<Object?> get props => [busy, problem];
}

/// Why a way to start failed.
enum SignedOutProblem() {
  /// No account has the GitHub account: GitHub makes none (ADR 0020, D25),
  /// so the person creates one where the instance offers a way.
  noGitHubAccount,

  /// The GitHub account's person signs in with their address and password
  /// now (ADR 0017).
  usePassword,

  /// GitHub signs nobody in here any more.
  gitHubEnded,

  /// Anything else, as no connection.
  failed,
}