import 'dart:convert';

import 'package:flutter/widgets.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:freezed_annotation/freezed_annotation.dart';
import 'package:shared_preferences/shared_preferences.dart';

import 'tracker_storage.dart';

part 'last_location.freezed.dart';
part 'last_location.g.dart';

/// The deepest route the user was viewing when the app was last active.
///
/// Encoded via [toRouteName] into [Route.settings.name] so a single
/// [NavigatorObserver] can track it without every screen needing to know
/// about persistence.
@freezed
class LastLocation with _$LastLocation {
  const LastLocation._();

  const factory LastLocation({required String trackerId, int? bookIndex}) =
      _LastLocation;

  factory LastLocation.fromJson(Map<String, dynamic> json) =>
      _$LastLocationFromJson(json);

  static const String _trackerPrefix = '/tracker/';

  String toRouteName() => bookIndex == null
      ? '$_trackerPrefix$trackerId'
      : '$_trackerPrefix$trackerId/book/$bookIndex';

  /// Parses a route name such as `/tracker/<id>` or
  /// `/tracker/<id>/book/<bookIndex>` back into a [LastLocation].
  ///
  /// Returns null for the root `/` route, unnamed routes (modals, dialogs),
  /// and malformed names.
  static LastLocation? tryParseRoute(String? name) {
    if (name == null) return null;
    final List<String> parts = name
        .split('/')
        .where((String s) => s.isNotEmpty)
        .toList(growable: false);
    if (parts.isEmpty || parts.first != 'tracker') return null;
    if (parts.length == 2) return LastLocation(trackerId: parts[1]);
    if (parts.length == 4 && parts[2] == 'book') {
      final int? idx = int.tryParse(parts[3]);
      if (idx != null) {
        return LastLocation(trackerId: parts[1], bookIndex: idx);
      }
    }
    return null;
  }
}

/// Reads and writes the most recent [LastLocation] to [SharedPreferences].
class LastLocationService {
  LastLocationService(this._prefs);

  static const String _key = 'bible_tracker.last_location.v1';

  final SharedPreferences _prefs;

  LastLocation? load() {
    final String? raw = _prefs.getString(_key);
    if (raw == null || raw.isEmpty) return null;
    try {
      return LastLocation.fromJson(jsonDecode(raw) as Map<String, dynamic>);
    } catch (_) {
      return null;
    }
  }

  Future<void> save(LastLocation? location) async {
    if (location == null) {
      await _prefs.remove(_key);
      return;
    }
    await _prefs.setString(_key, jsonEncode(location.toJson()));
  }
}

final Provider<LastLocationService> lastLocationServiceProvider =
    Provider<LastLocationService>(
      (Ref ref) => LastLocationService(ref.read(sharedPreferencesProvider)),
    );

/// Populated at startup in `main.dart` with the location that was persisted
/// during the previous session. Reading it once avoids a race where the root
/// navigator's initial `didPush` clears the saved value before the UI has
/// had a chance to restore it.
final Provider<LastLocation?> pendingRestoreProvider = Provider<LastLocation?>(
  (Ref ref) => null,
);

/// Writes the top-most named route to [_onChange] whenever navigation
/// changes. Unnamed routes (bottom sheets, dialogs, the create-tracker page)
/// are ignored so they don't clobber the underlying tracker/book location.
class LastLocationObserver extends NavigatorObserver {
  LastLocationObserver(this._onChange);

  final void Function(LastLocation? location) _onChange;

  @override
  void didPush(Route<dynamic> route, Route<dynamic>? previousRoute) {
    _notify(route);
  }

  @override
  void didPop(Route<dynamic> route, Route<dynamic>? previousRoute) {
    _notify(previousRoute);
  }

  @override
  void didReplace({Route<dynamic>? newRoute, Route<dynamic>? oldRoute}) {
    _notify(newRoute);
  }

  @override
  void didRemove(Route<dynamic> route, Route<dynamic>? previousRoute) {
    _notify(previousRoute);
  }

  void _notify(Route<dynamic>? route) {
    final String? name = route?.settings.name;
    if (name == null) return;
    if (name == '/') {
      _onChange(null);
      return;
    }
    final LastLocation? parsed = LastLocation.tryParseRoute(name);
    if (parsed != null) _onChange(parsed);
  }
}