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

import 'package:clock/clock.dart';
import 'package:halkyon_learn_flutter/src/core/content/payload.dart';
import 'package:halkyon_learn_flutter/src/feature/note/data/note_gateway.dart';

/// A [NoteGateway] in memory. Ids sort by creation, as UUID v7 ids do: notes
/// are `note-0001`, `note-0002`, …, revisions `nrev-0001`, …, each written
/// at the clock's time; [receiveRemoteRevision] plays a sync that brought
/// another device's edit.
class FakeNoteGateway() implements NoteGateway {
  final _notes = <String, ({String studysetId, String position})>{};
  final _revisions = <String, NoteRevisionRow>{};
  final _remoteChanges = StreamController<void>.broadcast();
  var _nextId = 1;

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

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

  /// When set, storing a note 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 noteId,
    required Set<String> parents,
    required ByteData payload,
  }) {
    _revisions[id] = (
      id: id,
      noteId: noteId,
      parents: parents,
      payload: payload,
      writtenAt: clock.now().toUtc(),
    );
    _remoteChanges.add(null);
  }

  /// Deletes the note [noteId] as if another device had done it and a sync
  /// had brought it here.
  void receiveRemoteDeletion(String noteId) {
    _notes.remove(noteId);
    _remoteChanges.add(null);
  }

  @override
  Future<List<NoteRow>> notesOf(String studysetId) async => [
    for (final MapEntry(key: id, value: note) in _notes.entries)
      if (note.studysetId == studysetId) (id: id, position: note.position),
  ];

  @override
  Future<List<NoteStampRow>> allNotes() async => [
    for (final MapEntry(key: id, value: note) in _notes.entries)
      (id: id, studysetId: note.studysetId),
  ];

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

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

  @override
  Future<String> insertRevision({
    required String noteId,
    required Set<String> parents,
    required ByteData payload,
  }) async {
    if (failWrites case final error?) {
      throw error;
    }
    final revision = (
      id: _newId('nrev'),
      noteId: noteId,
      parents: parents,
      payload: payload,
      writtenAt: clock.now().toUtc(),
    );
    _revisions[revision.id] = revision;
    written.add(revision);
    return revision.id;
  }

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

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

  @override
  Future<void> deleteNote(String noteId) async {
    deletions.add('delete $noteId');
    _notes.remove(noteId);
  }

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

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