import 'dart:io';

import 'package:flutter/foundation.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';
import 'package:timezone/data/latest.dart' as tz_data;
import 'package:timezone/timezone.dart' as tz;

/// Platform-agnostic contract for scheduling local (offline) reminders.
///
/// Presentation code depends only on this interface; the concrete
/// [PlatformNotificationService] wraps `flutter_local_notifications` so the
/// package never leaks into feature layers (architecture rule 1/2).
abstract class INotificationService {
  /// Prepares the underlying plugin. Safe to call repeatedly.
  Future<void> initialize();

  /// Requests OS-level notification permission.
  ///
  /// Returns `true` when alerts may be shown, `false` when the platform is
  /// unsupported or the user declined.
  Future<bool> requestPermissions();

  /// Schedules a one-shot reminder at [scheduledAt] and returns whether the
  /// platform accepted it. Times in the past are rejected.
  Future<bool> scheduleDoseReminder({
    required DateTime scheduledAt,
    required String title,
    required String body,
    int id = kDoseReminderNotificationId,
    String? payload,
  });

  /// Cancels the reminder registered under [id].
  Future<void> cancelReminder(int id);

  /// Cancels every pending reminder.
  Future<void> cancelAllReminders();
}

/// Stable notification id for the recurring dose reminder slot; re-using one
/// id replaces the previous scheduling instead of stacking duplicates.
const int kDoseReminderNotificationId = 7401;

/// `flutter_local_notifications`-backed implementation.
///
/// Support matrix (graceful degradation per architecture rule 3):
/// * **Android / iOS / macOS:** full one-shot scheduling via `zonedSchedule`.
/// * **Windows / Linux / Web:** scheduling is a logged no-op - the plugin has
///   no scheduler on those targets yet, and the domain keeps functioning
///   (in-app schedule view) without notifications.
class PlatformNotificationService implements INotificationService {
  PlatformNotificationService({FlutterLocalNotificationsPlugin? plugin})
      : _plugin = plugin ?? FlutterLocalNotificationsPlugin();

  static const String _channelId = 'medication_reminders';
  static const String _channelName = 'Medication Reminders';
  static const String _channelDescription =
      'Dose reminders for GLP-1 injections and site rotation.';

  static const NotificationDetails _notificationDetails = NotificationDetails(
    android: AndroidNotificationDetails(
      _channelId,
      _channelName,
      channelDescription: _channelDescription,
      importance: Importance.max,
      priority: Priority.high,
    ),
    iOS: DarwinNotificationDetails(),
    macOS: DarwinNotificationDetails(),
  );

  final FlutterLocalNotificationsPlugin _plugin;
  Future<void>? _initialization;

  /// Targets where the plugin can schedule future notifications.
  bool get _supportsScheduling =>
      !kIsWeb && (Platform.isAndroid || Platform.isIOS || Platform.isMacOS);

  @override
  Future<void> initialize() => _initialization ??= _initialize();

  Future<void> _initialize() async {
    if (!_supportsScheduling) return;

    // Time zones are initialized once; scheduling uses absolute UTC instants,
    // which the OS converts to the device's local time zone for display.
    tz_data.initializeTimeZones();

    // Permissions are requested explicitly via [requestPermissions] instead
    // of implicitly during initialize().
    const settings = InitializationSettings(
      android: AndroidInitializationSettings('@mipmap/ic_launcher'),
      iOS: DarwinInitializationSettings(
        requestAlertPermission: false,
        requestBadgePermission: false,
        requestSoundPermission: false,
      ),
      macOS: DarwinInitializationSettings(
        requestAlertPermission: false,
        requestBadgePermission: false,
        requestSoundPermission: false,
      ),
    );

    try {
      await _plugin.initialize(
        settings,
        onDidReceiveNotificationResponse: (response) {
          debugPrint('Notification tapped: ${response.payload}');
        },
      );
    } catch (error) {
      debugPrint('Notification initialization failed: $error');
    }
  }

  @override
  Future<bool> requestPermissions() async {
    if (!_supportsScheduling) return false;
    try {
      await initialize();

      if (Platform.isAndroid) {
        return await _plugin
                .resolvePlatformSpecificImplementation<
                    AndroidFlutterLocalNotificationsPlugin>()
                ?.requestNotificationsPermission() ??
            false;
      }
      // iOS and macOS share the Darwin permission surface.
      return await _plugin
              .resolvePlatformSpecificImplementation<
                  IOSFlutterLocalNotificationsPlugin>()
              ?.requestPermissions(alert: true, badge: true, sound: true) ??
          false;
    } catch (error) {
      debugPrint('Notification permission request failed: $error');
      return false;
    }
  }

  @override
  Future<bool> scheduleDoseReminder({
    required DateTime scheduledAt,
    required String title,
    required String body,
    int id = kDoseReminderNotificationId,
    String? payload,
  }) async {
    if (!_supportsScheduling) return false;
    if (!scheduledAt.isAfter(DateTime.now())) return false;

    try {
      await initialize();
      await _plugin.zonedSchedule(
        id,
        title,
        body,
        // Absolute instants; the tray renders them in device-local time.
        tz.TZDateTime.from(scheduledAt.toUtc(), tz.UTC),
        _notificationDetails,
        uiLocalNotificationDateInterpretation:
            UILocalNotificationDateInterpretation.absoluteTime,
        androidScheduleMode: AndroidScheduleMode.inexactAllowWhileIdle,
        payload: payload,
      );
      return true;
    } catch (error) {
      debugPrint('Dose reminder scheduling failed: $error');
      return false;
    }
  }

  @override
  Future<void> cancelReminder(int id) async {
    if (!_supportsScheduling) return;
    try {
      await initialize();
      await _plugin.cancel(id);
    } catch (error) {
      debugPrint('Notification cancel failed: $error');
    }
  }

  @override
  Future<void> cancelAllReminders() async {
    if (!_supportsScheduling) return;
    try {
      await initialize();
      await _plugin.cancelAll();
    } catch (error) {
      debugPrint('Notification cancel-all failed: $error');
    }
  }
}