import 'dart:async';
import 'dart:io';

import 'package:background_downloader/background_downloader.dart';
import 'package:flutter/foundation.dart';

import '../core/app_config.dart';
import '../services/token_store.dart';

class UploadRecord {
  const UploadRecord({
    required this.taskId,
    required this.name,
    required this.filename,
    required this.createdAt,
    this.progress = 0,
    this.status = TaskStatus.enqueued,
    this.sizeBytes = -1,
    this.errorMessage,
  });

  final String taskId;
  final String name;
  final String filename;
  final DateTime createdAt;
  final double progress;
  final TaskStatus status;
  final int sizeBytes;
  final String? errorMessage;

  bool get isFinished => status.isFinalState;
  bool get canRetry => status == TaskStatus.failed;

  UploadRecord copyWith({
    double? progress,
    TaskStatus? status,
    int? sizeBytes,
    String? errorMessage,
  }) => UploadRecord(
    taskId: taskId,
    name: name,
    filename: filename,
    createdAt: createdAt,
    progress: progress ?? this.progress,
    status: status ?? this.status,
    sizeBytes: sizeBytes ?? this.sizeBytes,
    errorMessage: errorMessage ?? this.errorMessage,
  );
}

class UploadController extends ChangeNotifier {
  UploadController(this._tokens) {
    _taskSubscription = FileDownloader().updates.listen(_onUpdate);
    _databaseSubscription = FileDownloader().database.updates.listen(
      _onDatabaseUpdate,
    );
    unawaited(_restoreHistory());
  }

  final TokenStore _tokens;
  late final StreamSubscription<TaskUpdate> _taskSubscription;
  late final StreamSubscription<TaskRecord> _databaseSubscription;
  final Map<String, UploadRecord> _uploads = {};
  final Map<String, Task> _tasks = {};
  bool _notificationPermissionChecked = false;
  bool _disposed = false;

  List<UploadRecord> get uploads {
    final result = _uploads.values.toList()
      ..sort((a, b) => b.createdAt.compareTo(a.createdAt));
    return result;
  }

  int completedVersion = 0;

  Future<void> _restoreHistory() async {
    // start() initializes tracking asynchronously during application startup.
    // A short retry also covers slower devices on their first launch.
    for (var attempt = 0; attempt < 3; attempt++) {
      try {
        final records = await FileDownloader().database.allRecords(
          group: 'uploads',
        );
        for (final record in records) {
          _storeDatabaseRecord(record);
        }
        if (!_disposed) notifyListeners();
        return;
      } catch (_) {
        await Future<void>.delayed(Duration(milliseconds: 400 * (attempt + 1)));
      }
    }
  }

  Future<void> refreshHistory() => _restoreHistory();

  Future<void> enqueue({
    required String filename,
    required String displayName,
    String? folderId,
  }) async {
    await _ensureNotificationPermission();
    final token = await _tokens.read();
    if (token == null) throw StateError('Your session has expired');
    final task = UploadTask(
      url: '${AppConfig.apiBaseUrl}/files/upload',
      filename: filename,
      directory: 'upload_queue',
      baseDirectory: BaseDirectory.applicationSupport,
      fileField: 'file',
      fields: folderId == null ? const {} : {'folderId': folderId},
      headers: {'Authorization': 'Bearer $token'},
      group: 'uploads',
      updates: Updates.statusAndProgress,
      retries: 2,
      displayName: displayName,
      metaData: displayName,
    );
    _tasks[task.taskId] = task;
    _uploads[task.taskId] = UploadRecord(
      taskId: task.taskId,
      name: displayName,
      filename: filename,
      createdAt: task.creationTime,
    );
    notifyListeners();
    final accepted = await FileDownloader().enqueue(task);
    if (!accepted) {
      _uploads[task.taskId] = _uploads[task.taskId]!.copyWith(
        status: TaskStatus.failed,
        errorMessage: 'The background upload queue rejected this file.',
      );
      notifyListeners();
      throw StateError('The background upload queue rejected this file');
    }
  }

  Future<void> _ensureNotificationPermission() async {
    if (_notificationPermissionChecked) return;
    _notificationPermissionChecked = true;
    final status = await FileDownloader().permissions.status(
      PermissionType.notifications,
    );
    if (status != PermissionStatus.granted) {
      await FileDownloader().permissions.request(PermissionType.notifications);
    }
  }

  void _onUpdate(TaskUpdate update) {
    _tasks[update.task.taskId] = update.task;
    final current = _uploads[update.task.taskId] ?? _fromTask(update.task);
    switch (update) {
      case TaskProgressUpdate():
        _uploads[update.task.taskId] = current.copyWith(
          progress: update.progress.clamp(0, 1),
        );
      case TaskStatusUpdate():
        _uploads[update.task.taskId] = current.copyWith(
          status: update.status,
          progress: update.status == TaskStatus.complete ? 1 : current.progress,
          errorMessage: update.exception?.description,
        );
        if (update.status == TaskStatus.complete) completedVersion++;
        if (update.status == TaskStatus.complete ||
            update.status == TaskStatus.canceled ||
            update.status == TaskStatus.notFound) {
          unawaited(_deleteStagedFile(update.task));
        }
    }
    notifyListeners();
  }

  void _onDatabaseUpdate(TaskRecord record) {
    if (record.group != 'uploads') return;
    _storeDatabaseRecord(record);
    if (!_disposed) notifyListeners();
  }

  void _storeDatabaseRecord(TaskRecord record) {
    _tasks[record.taskId] = record.task;
    _uploads[record.taskId] = UploadRecord(
      taskId: record.taskId,
      name: record.task.displayName,
      filename: record.task.filename,
      createdAt: record.task.creationTime,
      progress: record.progress.clamp(0, 1),
      status: record.status,
      sizeBytes: record.expectedFileSize,
      errorMessage: record.exception?.description,
    );
  }

  UploadRecord _fromTask(Task task) => UploadRecord(
    taskId: task.taskId,
    name: task.displayName,
    filename: task.filename,
    createdAt: task.creationTime,
  );

  Future<void> _deleteStagedFile(Task task) async {
    final file = File(await task.filePath());
    if (await file.exists()) await file.delete();
  }

  Future<void> cancel(String taskId) =>
      FileDownloader().cancelTaskWithId(taskId);

  Future<void> retry(String taskId) async {
    final original = _tasks[taskId];
    if (original is! UploadTask) {
      throw StateError('The original upload information is unavailable.');
    }
    final file = File(await original.filePath());
    if (!await file.exists()) {
      throw StateError(
        'The staged file is no longer available. Select it again.',
      );
    }
    final token = await _tokens.read();
    if (token == null) throw StateError('Your session has expired');
    final retried = original.copyWith(
      taskId: DateTime.now().microsecondsSinceEpoch.toString(),
      headers: {'Authorization': 'Bearer $token'},
      creationTime: DateTime.now(),
      retriesRemaining: original.retries,
    );
    _tasks[retried.taskId] = retried;
    _uploads[retried.taskId] = _fromTask(retried);
    notifyListeners();
    if (!await FileDownloader().enqueue(retried)) {
      _uploads[retried.taskId] = _uploads[retried.taskId]!.copyWith(
        status: TaskStatus.failed,
        errorMessage: 'The background upload queue rejected this retry.',
      );
      notifyListeners();
      throw StateError('The background upload queue rejected this retry.');
    }
  }

  Future<void> removeHistory(String taskId) async {
    final task = _tasks.remove(taskId);
    _uploads.remove(taskId);
    await FileDownloader().database.deleteRecordWithId(taskId);
    if (task != null && task.group == 'uploads') {
      await _deleteStagedFile(task);
    }
    notifyListeners();
  }

  Future<void> clearFinished() async {
    final finished = _uploads.values.where((item) => item.isFinished).toList();
    for (final item in finished) {
      await removeHistory(item.taskId);
    }
  }

  @override
  void dispose() {
    _disposed = true;
    _taskSubscription.cancel();
    _databaseSubscription.cancel();
    super.dispose();
  }
}