import 'dart:async';
import 'dart:typed_data';

import 'package:halkyon_learn_flutter/src/feature/profile/data/profile_gateway.dart';
import 'package:halkyon_learn_flutter/src/feature/profile/model/public_profile.dart';

/// A [ProfileGateway] in memory, on an instance whose account domain is
/// `halkyon.eu`: one profile, refusing the handles others have (whatever
/// their case) and, once its handle is fixed, any other handle.
class FakeProfileGateway({
  /// The person's profile; null while they have none.
  var PublicProfile? profile,

  /// Handles others have.
  final Set<String> taken = const {},

  /// Others' profiles, by their handles.
  final Map<String, PublicProfile> others = const {},
}) implements ProfileGateway {
  @override
  Future<PublicProfile?> byHandle(String handle) async {
    if (fail case final error?) {
      throw error;
    }
    return others[handle.toLowerCase()];
  }

  /// When set, every request fails with it.
  Exception? fail;

  @override
  Future<PublicProfile?> mine() async {
    if (fail case final error?) {
      throw error;
    }
    return profile;
  }

  /// The handles checked, in order.
  final checked = <String>[];

  @override
  Future<ProfileProblem?> checkHandle(String handle) async {
    if (fail case final error?) {
      throw error;
    }
    checked.add(handle);
    return _problemOf(handle);
  }

  ProfileProblem? _problemOf(String handle) {
    final current = profile;
    if (!RegExp(r'^[A-Za-z0-9_]{1,30}$').hasMatch(handle)) {
      return ProfileProblem.handleInvalid;
    }
    if (handle.toLowerCase() == 'admin') {
      return ProfileProblem.handleReserved;
    }
    if (taken.any((other) => other.toLowerCase() == handle.toLowerCase())) {
      return ProfileProblem.handleTaken;
    }
    if (current != null &&
        current.handleFixed &&
        current.handle.toLowerCase() != handle.toLowerCase()) {
      return ProfileProblem.published;
    }
    return null;
  }

  /// Every profile saved, in order.
  final saves = <PublicProfile>[];

  @override
  Future<PublicProfile> save({
    required String handle,
    required String displayName,
    required String bio,
    required List<String> links,
  }) async {
    if (fail case final error?) {
      throw error;
    }
    final current = profile;
    if (_problemOf(handle) case final problem?) {
      throw ProfileRefused(problem);
    }
    final saved = profile = PublicProfile(
      handle: handle,
      address: '$handle@halkyon.eu',
      displayName: displayName,
      bio: bio,
      links: links,
      // As the instance keeps them: those of links left as they were, under
      // the same handle.
      verifiedLinks: [
        if (current?.handle.toLowerCase() == handle.toLowerCase())
          for (final link in current?.verifiedLinks ?? const <String>[])
            if (links.contains(link)) link,
      ],
      pageUrl: 'https://halkyon.eu/@$handle',
      avatarUrl: current?.avatarUrl,
      handleFixed: current?.handleFixed ?? false,
    );
    saves.add(saved);
    return saved;
  }

  /// The avatars set, in order.
  final avatars = <Uint8List>[];

  @override
  Future<PublicProfile> setAvatar(Uint8List png) async {
    if (fail case final error?) {
      throw error;
    }
    avatars.add(png);
    final current = profile!;
    return profile = PublicProfile(
      handle: current.handle,
      address: current.address,
      displayName: current.displayName,
      bio: current.bio,
      links: current.links,
      avatarUrl: 'https://learn.halkyon.eu/avatars/${avatars.length}.png',
      handleFixed: current.handleFixed,
    );
  }

  @override
  Future<PublicProfile> removeAvatar() async {
    final current = profile!;
    return profile = PublicProfile(
      handle: current.handle,
      address: current.address,
      displayName: current.displayName,
      bio: current.bio,
      links: current.links,
      handleFixed: current.handleFixed,
    );
  }

  @override
  Future<void> remove() async {
    if (fail case final error?) {
      throw error;
    }
    if (profile?.handleFixed ?? false) {
      throw ProfileRefused(ProfileProblem.published);
    }
    profile = null;
  }

  /// The links whose pages link back to the profile page.
  final linkingBack = <String>{};

  /// How often the links were checked.
  int linkChecks = 0;

  /// While set, checking the links is refused as asked too often.
  bool refuseLinkChecks = false;

  /// While set, a check waits for it before it answers.
  Completer<void>? checkWaits;

  @override
  Future<PublicProfile> checkLinks() async {
    if (fail case final error?) {
      throw error;
    }
    if (refuseLinkChecks) {
      throw ProfileRefused(ProfileProblem.tooManyLinkChecks);
    }
    linkChecks++;
    // The profile as the check began, as an answer may come after a save.
    final began = profile!;
    await checkWaits?.future;
    final verified = [
      for (final link in began.links)
        if (linkingBack.contains(link)) link,
    ];
    profile = profile!.withVerifiedLinks(verified);
    return began.withVerifiedLinks(verified);
  }
}