import 'dart:math';

import 'package:device_info_plus/device_info_plus.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter/foundation.dart';
import 'package:shared_preferences/shared_preferences.dart';

/// Identifiers for this handset: one stable device id, one push token.
///
/// ── Neither of these may ever fail a sign-in ──
///
/// [ensureDeviceId] used to `throw` on every unhappy path — on an empty
/// hardware id, on a `PlatformException`, and on anything else it caught. It is
/// awaited on the line *before* the PIN check posts, inside the sign-in's outer
/// `try`, so a throw here never reached the network at all: the rider got
/// "Could not reach the server", pressed Retry, and the MPIN screen painted
/// **"Incorrect MPIN"** at him. For every phone number, on every attempt.
///
/// Two things made that certain rather than unlucky:
///
///  • It asked for `androidInfo` **unconditionally**. On iOS that call throws,
///    so no iPhone could ever complete a PIN login.
///  • The value is not even sent. `POST /miler/verify-pin` takes `phone`,
///    `pin`, `configid` and `device_token` — `deviceId` is dropped on the floor
///    inside `AuthProvider.login`. The sign-in was being aborted by a field the
///    sign-in does not use.
///
/// So: this file hands back a best-effort answer and **never throws**. A caller
/// that wants to know whether the answer is real can compare against
/// [unknownDeviceId]; nothing currently needs to.
class DeviceUtils {
  static const String _deviceIdKey = 'deviceId';
  static const String _fcmTokenKey = 'fcmToken';

  /// Prefix on ids this class generated rather than read off the hardware.
  static const String unknownDeviceId = 'generated-';

  /// A stable id for this install, persisted on first use.
  ///
  /// Hardware id where the platform has one — Android's `id`, iOS's
  /// `identifierForVendor` — and a persisted random id everywhere else, which
  /// is what the backend actually needs: something that does not change
  /// between launches. Never throws.
  static Future<String> ensureDeviceId(SharedPreferences prefs) async {
    final String? existing = prefs.getString(_deviceIdKey);
    if (existing != null && existing.isNotEmpty) return existing;

    String resolved = '';
    try {
      final info = DeviceInfoPlugin();
      switch (defaultTargetPlatform) {
        case TargetPlatform.android:
          resolved = (await info.androidInfo).id;
        case TargetPlatform.iOS:
          resolved = (await info.iosInfo).identifierForVendor ?? '';
        case TargetPlatform.macOS:
          resolved = (await info.macOsInfo).systemGUID ?? '';
        case TargetPlatform.windows:
          resolved = (await info.windowsInfo).deviceId;
        case TargetPlatform.linux:
          resolved = (await info.linuxInfo).machineId ?? '';
        case TargetPlatform.fuchsia:
          resolved = '';
      }
    } catch (e) {
      // A missing plugin, a denied permission, a simulator with no vendor id.
      // None of these are reasons to stop a rider signing in.
      debugPrint('[DEVICE] hardware id unavailable, generating one: $e');
    }

    if (resolved.trim().isEmpty) resolved = _generateId();
    await prefs.setString(_deviceIdKey, resolved);
    return resolved;
  }

  /// 128 bits of hex behind [unknownDeviceId], so a generated id is
  /// self-identifying in a log and cannot collide with a hardware one.
  static String _generateId() {
    final rand = Random.secure();
    final bytes = List<int>.generate(16, (_) => rand.nextInt(256));
    final hex = bytes.map((b) => b.toRadixString(16).padLeft(2, '0')).join();
    return '$unknownDeviceId$hex';
  }

  /// The FCM registration token, or `''` when push is unavailable.
  ///
  /// Already total, and stays that way: a rider who declined notifications
  /// still has a day's work to do.
  static Future<String> ensureFcmToken(SharedPreferences prefs) async {
    try {
      final String? existing = prefs.getString(_fcmTokenKey);
      if (existing != null && existing.isNotEmpty) {
        return existing;
      }
      if (Firebase.apps.isEmpty) {
        try {
          await Firebase.initializeApp();
        } catch (_) {
          return '';
        }
      }
      final FirebaseMessaging messaging = FirebaseMessaging.instance;
      final NotificationSettings settings = await messaging.requestPermission(
        alert: true,
        badge: true,
        sound: true,
      );
      if (settings.authorizationStatus == AuthorizationStatus.authorized ||
          settings.authorizationStatus == AuthorizationStatus.provisional) {
        final String? token = await messaging.getToken();
        if (token != null && token.isNotEmpty) {
          await prefs.setString(_fcmTokenKey, token);
          return token;
        }
      }
    } catch (_) {}
    return '';
  }
}