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

import 'package:halkyon_learn_flutter/src/core/content/payload.dart';
import 'package:halkyon_learn_flutter/src/feature/card/data/card_gateway.dart';

/// A [CardGateway] in memory. Ids sort by creation, as UUID v7 ids do: cards
/// are `card-0001`, `card-0002`, …, revisions `rev-0001`, …;
/// [receiveRemoteRevision] plays a sync that brought another device's edit.
class FakeCardGateway() implements CardGateway {
  final _cards = <String, ({String studysetId, String position})>{};
  final _revisions = <String, CardRevisionRow>{};
  final _remoteChanges = StreamController<void>.broadcast();
  var _nextId = 1;

  /// Every revision written on this device, in order.
  final written = <CardRevisionRow>[];

  /// The deletion steps, in order: `blank <card id>`, `delete <card id>`.
  final deletions = <String>[];

  /// When set, storing a card or a revision fails with it.
  Exception? failWrites;

  /// The payload each revision holds now, by revision id.
  Map<String, ByteData> get payloads => {
    for (final revision in _revisions.values) revision.id: revision.payload,
  };

  /// Stores a revision as if another device had written it and a sync had
  /// brought it here.
  void receiveRemoteRevision({
    required String id,
    required String cardId,
    required Set<String> parents,
    required ByteData payload,
  }) {
    _revisions[id] = (
      id: id,
      cardId: cardId,
      parents: parents,
      payload: payload,
    );
    _remoteChanges.add(null);
  }

  @override
  Future<List<CardRow>> cardsOf(String studysetId) async => [
    for (final MapEntry(key: id, value: card) in _cards.entries)
      if (card.studysetId == studysetId) (id: id, position: card.position),
  ];

  @override
  Future<List<CardRevisionRow>> revisionsOf(Set<String> cardIds) async => [
    for (final revision in _revisions.values)
      if (cardIds.contains(revision.cardId)) revision,
  ];

  @override
  Future<String> insertCard({
    required String studysetId,
    required String position,
    required ByteData payload,
  }) async {
    if (failWrites case final error?) {
      throw error;
    }
    final id = _newId('card');
    _cards[id] = (studysetId: studysetId, position: position);
    await insertRevision(cardId: id, parents: const {}, payload: payload);
    return id;
  }

  @override
  Future<void> insertRevision({
    required String cardId,
    required Set<String> parents,
    required ByteData payload,
  }) async {
    if (failWrites case final error?) {
      throw error;
    }
    final revision = (
      id: _newId('rev'),
      cardId: cardId,
      parents: parents,
      payload: payload,
    );
    _revisions[revision.id] = revision;
    written.add(revision);
  }

  @override
  Future<void> updatePosition(String cardId, String position) async {
    if (_cards[cardId] case final card?) {
      _cards[cardId] = (studysetId: card.studysetId, position: position);
    }
  }

  @override
  Future<void> blankRevisions(String cardId) async {
    deletions.add('blank $cardId');
    for (final revision in [..._revisions.values]) {
      if (revision.cardId == cardId) {
        _revisions[revision.id] = (
          id: revision.id,
          cardId: cardId,
          parents: revision.parents,
          payload: redactedPayload,
        );
      }
    }
  }

  @override
  Future<void> deleteCard(String cardId) async {
    deletions.add('delete $cardId');
    _cards.remove(cardId);
  }

  @override
  Stream<void> get remoteChanges => _remoteChanges.stream;

  String _newId(String kind) =>
      '$kind-${(_nextId++).toString().padLeft(4, '0')}';
}