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

import 'package:ota_update/ota_update.dart';
import 'package:package_info_plus/package_info_plus.dart';
import 'package:permission_handler/permission_handler.dart';
import 'package:supabase_flutter/supabase_flutter.dart';

import '../models/app_version.dart';

/// Handles the business logic for fetching version information from the
/// ``app_versions`` table and downloading/installing a replacement APK.
///
/// This class is intentionally *not* coupled to any UI framework so that it can
/// be unit‑tested easily.  Widgets should only call into the public methods and
/// display whatever progress / error states they need.
class AppUpdateService {
  AppUpdateService._();

  /// Public singleton that other parts of the app can depend on.  The private
  /// constructor prevents instantiation from tests; they should mock the
  /// individual methods instead.
  static final instance = AppUpdateService._();

  final SupabaseClient _client = Supabase.instance.client;

  /// Fetches the most recent record from ``app_versions``.  The table is
  /// expected to contain a single row per release; we use the highest
  /// ``version_code`` so that historical entries may be kept if desired.
  Future<AppVersion?> _fetchLatestVersion() async {
    try {
      final Map<String, dynamic>? data = await _client
          .from('app_versions')
          .select()
          .order('version_code', ascending: false)
          .limit(1)
          .maybeSingle();
      if (data == null) return null;
      return AppVersion.fromMap(data);
    } catch (e) {
      // rethrow so callers can handle/log
      rethrow;
    }
  }

  /// Compare the running build number with the latest data from the server and
  /// return an [AppUpdateInfo] object describing the relationship.  Errors
  /// (network down, no supabase instance) are simply re‑thrown; the caller can
  /// decide whether to ignore them or surface them to the user.
  Future<AppUpdateInfo> checkForUpdate() async {
    final pkg = await PackageInfo.fromPlatform();
    final currentBuild = int.tryParse(pkg.buildNumber) ?? 0;

    final serverVersion = await _fetchLatestVersion();

    if (serverVersion == null) {
      // table empty – nothing to do
      return AppUpdateInfo(
        currentBuildNumber: currentBuild,
        latestVersion: null,
        isUpdateAvailable: false,
        isForceUpdate: false,
      );
    }

    final available = currentBuild < serverVersion.versionCode;
    final force = currentBuild < serverVersion.minVersionRequired;

    return AppUpdateInfo(
      currentBuildNumber: currentBuild,
      latestVersion: serverVersion,
      isUpdateAvailable: available,
      isForceUpdate: force,
    );
  }

  /// Downloads and installs the APK at [downloadUrl] using `ota_update`.
  /// Progress is surfaced via [onProgress] (0.0–1.0).  The returned future
  /// completes once the download has finished and installation has started.
  ///
  /// Throws on permission denial or when the OTA stream reports an error.
  Future<void> downloadAndInstallApk(
    String downloadUrl, {
    required void Function(double) onProgress,
  }) async {
    if (!Platform.isAndroid) {
      throw UnsupportedError(
        'In‑app updates currently only supported on Android',
      );
    }

    final status = await Permission.requestInstallPackages.request();
    if (!status.isGranted) {
      throw Exception('installation permission denied');
    }

    final completer = Completer<void>();
    StreamSubscription<OtaEvent>? sub;
    try {
      sub = OtaUpdate()
          .execute(
            downloadUrl,
            destinationFilename:
                'app_${DateTime.now().millisecondsSinceEpoch}.apk',
          )
          .listen(
            (event) {
              switch (event.status) {
                case OtaStatus.DOWNLOADING:
                  final pct = double.tryParse(event.value ?? '0') ?? 0;
                  onProgress(pct / 100.0);
                  break;
                case OtaStatus.INSTALLING:
                  if (!completer.isCompleted) completer.complete();
                  break;
                default:
                  // treat all other statuses as failure; they provide a string
                  // description in `event.value`.
                  if (!completer.isCompleted) {
                    completer.completeError(
                      Exception('OTA update failed: ${event.status}'),
                    );
                  }
                  break;
              }
            },
            onError: (e) {
              if (!completer.isCompleted) completer.completeError(e);
            },
          );
      await completer.future;
    } finally {
      if (sub != null) await sub.cancel();
    }
  }
}