import 'dart:async';

import 'package:crdt_sync/crdt_sync.dart';
import 'package:todo/data/note.dart';
import 'package:todo/data/note_import.dart';
import 'package:todo/data/note_query.dart';
import 'package:todo/data/note_record.dart';

export 'package:todo/data/note_import.dart';
export 'package:todo/data/note_query.dart';
export 'package:todo/data/note_record.dart';

// Deliberately free of `dart:io`: the desktop app is a web build, and a single
// `dart:io` import anywhere in the graph makes the whole app fail to compile
// for web. Opening a repository for a real platform lives behind the
// conditional export in `repository_factory.dart`; the legacy sqlite migration
// lives in the io-only `legacy_sqlite_migration.dart`.

/// Local-first persistence for [Note]s, backed by the shared `crdt_sync`
/// [LogStore] (was `sqlite_crdt`).
///
/// Every write goes straight to local storage so the app works fully offline.
/// Each [Note] is stored *as* a crdt_sync [Record] (id + per-field
/// last-writer-wins map + sticky tombstone), so the on-disk log **is** the
/// sync wire format — no separate adapter. Filtering and sorting run in Dart
/// over the in-memory log (the record fields are opaque to the library); the
/// note count of a personal backlog is small enough that this is cheap. This
/// class owns the note↔record mapping and exposes a small, intention-revealing
/// API; the log never leaks past this boundary.
class NoteRepository {
  NoteRepository._(this._store, this._nodeId);

  final LogStore _store;
  final String _nodeId;

  /// Fires after each successful write ([upsert], [delete], [importLog], and
  /// transitively [importNotes]). Emits `void` — pull the data on demand.
  Stream<void> get changes => _store.changes;

  /// SharedPreferences key holding this device's stable CRDT node id.
  static const kNodeId = 'crdt.nodeId';

  /// SharedPreferences key recording that the legacy sqlite import already ran.
  static const kMigrated = 'crdt.migratedFromSqlite';

  /// File name of the persisted log, used by the io factory.
  static const logFileName = 'todo_notes.json';

  /// Opens (or creates) the note log backed by [persistence].
  ///
  /// Platform wiring — where the log lives, and the one-time legacy sqlite
  /// import — belongs to the callers in `repository_factory_*.dart`, so that
  /// this class stays free of `dart:io` and can compile for web.
  static Future<NoteRepository> openWith({
    required LogPersistence persistence,
    required String nodeId,
  }) async {
    final store = LogStore(persistence: persistence, nodeId: nodeId);
    await store.load();
    return NoteRepository._(store, nodeId);
  }

  /// Replaces the whole log, used by the one-time legacy sqlite migration.
  ///
  /// Distinct from [importLog], which merges: migration seeds a store that is
  /// known to be empty and must preserve the records' own clocks verbatim.
  Future<void> seedFrom(Log log) async {
    if (log.isNotEmpty) await _store.replaceAll(log);
  }

  /// Opens a transient in-memory log; intended for tests.
  static Future<NoteRepository> openInMemory({
    String nodeId = 'test-node',
  }) async {
    final store = LogStore(persistence: MemoryPersistence(), nodeId: nodeId);
    await store.load();
    return NoteRepository._(store, nodeId);
  }

  /// Builds a record whose field clocks come from the note's own `updatedAt`
  /// rather than from "now".
  ///
  /// Used by every path that *restores* notes the user already had — the
  /// legacy sqlite migration, backup recovery, and file import. Stamping "now"
  /// there is actively harmful: under per-field last-writer-wins, a restored
  /// copy would outrank the same note on every other device, so a device that
  /// recovered from a backup would silently overwrite newer edits made
  /// elsewhere. Seeding from real edit time makes a restore lose to genuinely
  /// newer data, which is what a restore should do.
  ///
  /// Public because the legacy migration lives in an io-only library that
  /// cannot reach private members here.
  static Record recordAtNoteTime(
    Note note,
    String nodeId, {
    bool deleted = false,
  }) {
    final hlc = Hlc(
      wallTimeMs: note.updatedAt.millisecondsSinceEpoch,
      counter: 0,
      nodeId: nodeId,
    );
    return Record(
      id: note.id,
      fields: noteFields(note, hlc),
      deleted: deleted,
      deletedHlc: deleted ? hlc : null,
    );
  }

  /// Inserts a new note or updates the existing one with the same [id].
  ///
  /// This is the single write path used by the capture screen's
  /// character-by-character autosave: it is cheap and idempotent. All fields
  /// share one fresh monotonic clock (they are written together).
  Future<void> upsert(Note note) async {
    await _store.upsert(
      Record(id: note.id, fields: noteFields(note, _store.nextHlc())),
    );
  }

  /// Soft-deletes a note. The log keeps a sticky tombstone so the deletion
  /// propagates on the next sync instead of resurrecting the record.
  Future<void> delete(String id) => _store.delete(id);

  /// Merges [incoming] notes (e.g. from an imported file) into local storage.
  ///
  /// Safe by design — it never destroys a *newer* local edit: an incoming
  /// note overwrites the local one only when its [Note.updatedAt] is strictly
  /// newer, or when the id is not present locally. Re-importing a stale backup
  /// is therefore a no-op for notes you've since edited. Notes absent from
  /// [incoming] are kept.
  Future<ImportOutcome> importNotes(List<Note> incoming) async {
    final existing = {for (final n in _liveNotes()) n.id: n};
    var added = 0;
    var updated = 0;
    var skipped = 0;
    for (final note in incoming) {
      final local = existing[note.id];
      // Restore at the note's own edit time, never "now" — see
      // [recordAtNoteTime]. The freshness check above is what decides whether
      // the import wins locally; the clock decides whether it wins on *other*
      // devices, and an import must not win there simply by being recent.
      if (local == null) {
        await _store.upsert(recordAtNoteTime(note, _nodeId));
        added++;
      } else if (note.updatedAt.isAfter(local.updatedAt)) {
        await _store.upsert(recordAtNoteTime(note, _nodeId));
        updated++;
      } else {
        skipped++;
      }
    }
    return ImportOutcome(added: added, updated: updated, skipped: skipped);
  }

  /// Returns the live notes matching [filter], ordered by [sort].
  Future<List<Note>> listNotes({
    NoteSort sort = NoteSort.priorityDesc,
    NoteFilter filter = const NoteFilter(),
  }) async => _query(sort, filter);

  /// Emits the matching, ordered note list immediately and re-emits whenever
  /// the log changes, so the UI stays in sync without manual refreshes.
  Stream<List<Note>> watchNotes({
    NoteSort sort = NoteSort.priorityDesc,
    NoteFilter filter = const NoteFilter(),
  }) => _watch(() => _query(sort, filter));

  /// Emits the live count of non-deleted notes immediately and on each change.
  Stream<int> watchCount() => _watch(_liveCount);

  /// A stream that emits `compute()` synchronously when first listened to (the
  /// seed), then again on every log change. Seeding in `onListen` — rather than
  /// lazily in an `async*` body — avoids a race where a write between `listen`
  /// and the first generator tick would swallow the initial snapshot.
  Stream<T> _watch<T>(T Function() compute) {
    StreamSubscription<void>? sub;
    late final StreamController<T> controller;
    controller = StreamController<T>(
      onListen: () {
        controller.add(compute());
        sub = _store.changes.listen((_) => controller.add(compute()));
      },
      onCancel: () => sub?.cancel(),
    );
    return controller.stream;
  }

  /// This device's stable node id. Names its file in the sync repo so two
  /// devices never write the same path.
  String get nodeId => _nodeId;

  /// Returns this device's full note log for upload.
  Log exportLog() => _store.snapshot();

  /// Merges a remote log into local storage (conflict-free, per-field
  /// last-writer-wins with sticky deletes via [mergeLogs]).
  Future<void> importLog(Log remote) async {
    await _store.replaceAll(mergeLogs(_store.snapshot(), remote));
  }

  /// Closes the underlying log and its change stream.
  Future<void> close() => _store.close();

  // --- querying (the note <-> record mapping is in note_record.dart) --------

  Iterable<Note> _liveNotes() =>
      _store.values.where((r) => !r.deleted).map(noteFromRecord);

  int _liveCount() => _store.values.where((r) => !r.deleted).length;

  List<Note> _query(NoteSort sort, NoteFilter filter) {
    final notes = _liveNotes().where((n) => matchesFilter(n, filter)).toList()
      ..sort(comparatorFor(sort));
    return notes;
  }
}