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

import 'package:ota_update/ota_update.dart';
import 'package:package_info_plus/package_info_plus.dart';
import 'package:pub_semver/pub_semver.dart';
import 'package:permission_handler/permission_handler.dart';
import 'package:flutter/services.dart';
import 'package:flutter/foundation.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;

  static const MethodChannel _platform = MethodChannel('tasq/ota');

  // Smoothed progress state — the service smooths raw percent updates into
  // small animated increments so UI progress displays feel responsive.
  double _smoothedProgress = 0.0;
  double _smoothedTarget = 0.0;
  Timer? _smoothedTimer;

  Future<void> _openUnknownAppSourcesSettings() async {
    try {
      await _platform.invokeMethod('openUnknownSources');
    } on PlatformException {
      // ignore if platform method is not implemented
    }
  }

  /// 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 {
      // Request all rows so we can compare semantic versions locally. The
      // Supabase client returns a List for select() (maybeSingle returns a Map).
      final data = await _client.from('app_versions').select();
      // The Supabase client returns a PostgrestList (List-like). Convert to
      // a Dart List and pick the highest semantic version.
      final list = data as List;
      if (list.isEmpty) return null;

      Version? best;
      Map<String, dynamic>? bestRow;
      for (final item in list) {
        if (item is Map) {
          final map = Map<String, dynamic>.from(item);
          final v = map['version_code']?.toString() ?? '';
          try {
            final parsed = Version.parse(v);
            if (best == null || parsed > best) {
              best = parsed;
              bestRow = map;
            }
          } catch (_) {
            // ignore non-semver rows
          }
        }
      }
      if (bestRow != null) return AppVersion.fromMap(bestRow);
      // fallback to the first row
      return AppVersion.fromMap(Map<String, dynamic>.from(list.first));
    } catch (e) {
      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 {
    // only run on Android devices; web and other platforms skip
    if (!Platform.isAndroid) {
      return AppUpdateInfo(
        currentBuildNumber: '',
        latestVersion: null,
        isUpdateAvailable: false,
        isForceUpdate: false,
      );
    }

    final pkg = await PackageInfo.fromPlatform();
    // prefer the version name which commonly holds semantic versions like
    // "1.2.3". fall back to buildNumber when version is empty.
    final ver = pkg.version.trim();
    final build = pkg.buildNumber.trim();
    final currentVersion = ver.isNotEmpty ? ver : build;

    final serverVersion = await _fetchLatestVersion();

    if (serverVersion == null) {
      return AppUpdateInfo(
        currentBuildNumber: currentVersion,
        latestVersion: null,
        isUpdateAvailable: false,
        isForceUpdate: false,
      );
    }

    // compare using semantic versioning where possible
    Version safeParse(String s) {
      try {
        return Version.parse(s);
      } catch (_) {
        return Version(0, 0, 0);
      }
    }

    final vCurrent = safeParse(currentVersion);
    final vLatest = safeParse(serverVersion.versionCode);
    final vMin = safeParse(serverVersion.minVersionRequired);

    final available = vCurrent < vLatest;
    final force = vCurrent < vMin;

    return AppUpdateInfo(
      currentBuildNumber: currentVersion,
      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) {
      // Open the system settings page so the user can enable "Install unknown apps"
      try {
        await _openUnknownAppSourcesSettings();
      } catch (_) {}
      throw Exception('installation permission denied; opened settings');
    }

    // Wrap OTA download in a retry loop to handle transient network issues
    // (socket closed / timeout) that the underlying okhttp client may throw.
    const int maxAttempts = 3;
    for (int attempt = 1; attempt <= maxAttempts; attempt++) {
      final completer = Completer<void>();
      StreamSubscription<OtaEvent>? sub;
      try {
        debugPrint('OTA: starting attempt $attempt/$maxAttempts');
        sub = OtaUpdate()
            .execute(
              downloadUrl,
              destinationFilename:
                  'app_${DateTime.now().millisecondsSinceEpoch}.apk',
            )
            .listen(
              (event) {
                final statusStr = event.status.toString();
                // DOWNLOADING usually reports percent in event.value
                if (statusStr.endsWith('DOWNLOADING')) {
                  final pct = double.tryParse(event.value ?? '0') ?? 0;
                  try {
                    _setSmoothedProgress(pct / 100.0, onProgress);
                  } catch (_) {}
                } else if (statusStr.endsWith('INSTALLING')) {
                  if (!completer.isCompleted) completer.complete();
                } else if (statusStr.toLowerCase().contains('cancel')) {
                  if (!completer.isCompleted) {
                    completer.completeError(
                      Exception('OTA cancelled: ${event.value ?? ''}'),
                    );
                  }
                } else if (statusStr.toLowerCase().contains('permission') ||
                    (event.value ?? '').toLowerCase().contains('permission')) {
                  try {
                    _openUnknownAppSourcesSettings();
                  } catch (_) {}
                  if (!completer.isCompleted) {
                    completer.completeError(
                      Exception(
                        'OTA permission not granted: ${event.value ?? ''}',
                      ),
                    );
                  }
                } else {
                  // Only treat events containing known network/error keywords as fatal
                  final val = (event.value ?? '').toLowerCase();
                  if (val.contains('timeout') ||
                      val.contains('socket') ||
                      val.contains('closed') ||
                      statusStr.toLowerCase().contains('error')) {
                    if (!completer.isCompleted) {
                      completer.completeError(
                        Exception(
                          'OTA update failed ($statusStr): ${event.value ?? ''}',
                        ),
                      );
                    }
                  } else {
                    // Unknown non-error status — ignore to avoid premature failure.
                  }
                }
              },
              onError: (e) {
                if (!completer.isCompleted) completer.completeError(e);
              },
            );

        await completer.future;
        debugPrint('OTA: attempt $attempt succeeded');
        return;
      } catch (e, st) {
        debugPrint('OTA: attempt $attempt failed: $e\n$st');
        // If last attempt, rethrow so caller can handle/report it.
        if (attempt == maxAttempts) rethrow;

        final msg = e.toString();
        // Retry only on network/timeouts/socket-related failures.
        if (msg.toLowerCase().contains('timeout') ||
            msg.toLowerCase().contains('socket') ||
            msg.toLowerCase().contains('closed')) {
          final backoff = Duration(seconds: 2 * attempt);
          debugPrint('OTA: retrying after ${backoff.inSeconds}s backoff');
          await Future.delayed(backoff);
          continue; // next attempt
        }

        // For non-network errors, do not retry.
        rethrow;
      } finally {
        if (sub != null) await sub.cancel();
        _smoothedTimer?.cancel();
        _smoothedTimer = null;
      }
    }
    // If we reach here all ota_update attempts failed; try a Dart HTTP download
    // to a temp file and ask native code to install it via FileProvider.
    try {
      debugPrint('OTA: falling back to Dart HTTP download');
      final filePath = await _downloadApkToFile(downloadUrl, onProgress);
      try {
        await _platform.invokeMethod('installApk', {'path': filePath});
      } on PlatformException catch (e) {
        throw Exception('Failed to invoke native installer: ${e.message}');
      }
    } catch (e) {
      rethrow;
    }
  }

  Future<String> _downloadApkToFile(
    String url,
    void Function(double) onProgress,
  ) async {
    final uri = Uri.parse(url);
    final client = HttpClient();
    client.connectionTimeout = const Duration(minutes: 5);
    final req = await client.getUrl(uri);
    final resp = await req.close();
    if (resp.statusCode != 200) {
      throw Exception('Download failed: HTTP ${resp.statusCode}');
    }

    final tempDir = Directory.systemTemp.createTempSync('ota_');
    final file = File(
      '${tempDir.path}/app_${DateTime.now().millisecondsSinceEpoch}.apk',
    );
    final sink = file.openWrite();
    final contentLength = resp.contentLength;
    int received = 0;
    try {
      await for (final chunk in resp) {
        received += chunk.length;
        sink.add(chunk);
        if (contentLength > 0) {
          try {
            _setSmoothedProgress(received / contentLength, onProgress);
          } catch (_) {}
        }
      }
    } finally {
      await sink.close();
      client.close(force: true);
      _smoothedTimer?.cancel();
      _smoothedTimer = null;
      _smoothedProgress = 0.0;
    }
    return file.path;
  }

  void _setSmoothedProgress(double target, void Function(double) onProgress) {
    // Clamp
    target = target.clamp(0.0, 1.0);

    // If target is less than or equal to current, update immediately.
    if (target <= _smoothedProgress) {
      _smoothedTarget = target;
      _smoothedProgress = target;
      try {
        onProgress(_smoothedProgress);
      } catch (_) {}
      return;
    }

    // Otherwise, set the target and ensure a single periodic timer is running
    // which will nudge _smoothedProgress toward _smoothedTarget. This avoids
    // canceling/creating timers on every small update which caused batching.
    _smoothedTarget = target;
    if (_smoothedTimer != null) return;

    const tickMs = 100;
    _smoothedTimer = Timer.periodic(const Duration(milliseconds: tickMs), (t) {
      // Move a fraction toward the target for a smooth ease-out feel.
      final remaining = _smoothedTarget - _smoothedProgress;
      final step = (remaining * 0.5).clamp(0.002, 0.05);
      _smoothedProgress = (_smoothedProgress + step).clamp(0.0, 1.0);
      try {
        onProgress(_smoothedProgress);
      } catch (_) {}
      // Stop when we're very close to the target.
      if ((_smoothedTarget - _smoothedProgress) < 0.001) {
        _smoothedProgress = _smoothedTarget;
        try {
          onProgress(_smoothedProgress);
        } catch (_) {}
        _smoothedTimer?.cancel();
        _smoothedTimer = null;
      }
    });
  }
}