import 'dart:async';
import 'dart:convert';

import 'package:crypto/crypto.dart';
import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;

@immutable
class R2DownloadResult {
  final bool success;
  final String? cloudRideId;
  final Uint8List? zipBytes;
  final String? sha256Hash;
  final String? etag;
  final String? errorMessage;
  final int? statusCode;
  final bool isRetryable;
  final bool requiresAuth;

  const R2DownloadResult({
    required this.success,
    this.cloudRideId,
    this.zipBytes,
    this.sha256Hash,
    this.etag,
    this.errorMessage,
    this.statusCode,
    this.isRetryable = true,
    this.requiresAuth = false,
  });

  const R2DownloadResult.success({
    required String cloudRideId,
    required Uint8List zipBytes,
    required String sha256Hash,
    String? etag,
  }) : this(
          success: true,
          cloudRideId: cloudRideId,
          zipBytes: zipBytes,
          sha256Hash: sha256Hash,
          etag: etag,
          statusCode: 200,
          isRetryable: false,
        );

  const R2DownloadResult.authRequired(String message, {int statusCode = 401})
      : this(
          success: false,
          errorMessage: message,
          statusCode: statusCode,
          isRetryable: true,
          requiresAuth: true,
        );

  const R2DownloadResult.temporaryFailure(String message, {int? statusCode})
      : this(success: false, errorMessage: message, statusCode: statusCode, isRetryable: true);

  const R2DownloadResult.permanentFailure(String message, {int? statusCode})
      : this(success: false, errorMessage: message, statusCode: statusCode, isRetryable: false);
}

/// Downloads a verified telemetry bundle through the authenticated Worker gateway.
/// The Worker authorizes the ride, and this service verifies the returned SHA-256
/// before exposing the bytes to restore code.
class R2DownloadService {
  static const String defaultWorkerUrl = String.fromEnvironment(
    'R2_WORKER_URL',
    defaultValue: 'https://motorsignal-r2-worker.bponders12.workers.dev',
  );

  final http.Client _client;
  final String _workerBaseUrl;

  R2DownloadService({http.Client? client, String? workerBaseUrl})
      : _client = client ?? http.Client(),
        _workerBaseUrl = (workerBaseUrl ?? defaultWorkerUrl).replaceAll(RegExp(r'/+$'), '');

  String get workerBaseUrl => _workerBaseUrl;

  Future<R2DownloadResult> downloadTelemetryBundle({
    required String idToken,
    required String cloudRideId,
    Duration timeout = const Duration(seconds: 45),
  }) async {
    if (idToken.trim().isEmpty) {
      return const R2DownloadResult.authRequired('Firebase ID token is required for R2 download.');
    }
    if (!RegExp(r'^ride_[A-Za-z0-9_-]+$').hasMatch(cloudRideId)) {
      return const R2DownloadResult.permanentFailure('Invalid cloud ride identifier.', statusCode: 400);
    }

    try {
      final uri = Uri.parse('$_workerBaseUrl/r2/download').replace(
        queryParameters: {'rideId': cloudRideId},
      );
      final response = await _client.get(
        uri,
        headers: {
          'Authorization': 'Bearer ${idToken.trim()}',
          'Accept': 'application/zip',
        },
      ).timeout(timeout);

      final status = response.statusCode;
      if (status == 401 || status == 403) {
        return R2DownloadResult.authRequired(
          'R2 Worker authorization denied ($status).',
          statusCode: status,
        );
      }
      if (status == 404) {
        return R2DownloadResult.permanentFailure(
          'Telemetry bundle is not available in MotorCloud.',
          statusCode: status,
        );
      }
      if (status == 409 || status == 422) {
        return R2DownloadResult.permanentFailure(
          'MotorCloud rejected the telemetry bundle integrity or ownership metadata.',
          statusCode: status,
        );
      }
      if (status < 200 || status >= 300) {
        return R2DownloadResult.temporaryFailure(
          'R2 Worker temporary error ($status).',
          statusCode: status,
        );
      }

      final returnedRideId = response.headers['x-motorsignal-ride-id'];
      if (returnedRideId != cloudRideId) {
        return const R2DownloadResult.permanentFailure(
          'R2 Worker returned an unexpected cloud ride identifier.',
          statusCode: 422,
        );
      }

      final expectedSha256 = response.headers['x-motorsignal-sha256']?.trim().toLowerCase();
      if (expectedSha256 == null || !RegExp(r'^[a-f0-9]{64}$').hasMatch(expectedSha256)) {
        return const R2DownloadResult.permanentFailure(
          'R2 Worker did not provide a valid telemetry SHA-256.',
          statusCode: 422,
        );
      }

      final bytes = Uint8List.fromList(response.bodyBytes);
      if (bytes.isEmpty) {
        return const R2DownloadResult.permanentFailure('Downloaded telemetry bundle is empty.', statusCode: 422);
      }

      final actualSha256 = sha256.convert(bytes).toString().toLowerCase();
      if (actualSha256 != expectedSha256) {
        return const R2DownloadResult.permanentFailure(
          'Telemetry bundle SHA-256 verification failed.',
          statusCode: 422,
        );
      }

      return R2DownloadResult.success(
        cloudRideId: cloudRideId,
        zipBytes: bytes,
        sha256Hash: actualSha256,
        etag: response.headers['etag'],
      );
    } on TimeoutException {
      return R2DownloadResult.temporaryFailure(
        'Download from Cloudflare R2 timed out after ${timeout.inSeconds} seconds.',
      );
    } on FormatException catch (e) {
      return R2DownloadResult.permanentFailure('Invalid R2 download response: $e', statusCode: 422);
    } catch (e) {
      return R2DownloadResult.temporaryFailure('Network error downloading from Cloudflare R2: $e');
    }
  }

  /// Useful when the Worker returns a JSON error body for diagnostics.
  static String errorBody(http.Response response) {
    try {
      final decoded = jsonDecode(response.body);
      if (decoded is Map && decoded['error'] is String) return decoded['error'] as String;
    } catch (_) {}
    return 'R2 Worker request failed (${response.statusCode}).';
  }
}