import 'dart:convert';
import 'dart:io';

import 'package:crypto/crypto.dart';
import 'package:dio/dio.dart';
import 'package:flutter/foundation.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:uuid/uuid.dart';
import 'package:worldhopper/models/koreader_progress.dart';
import 'package:worldhopper/models/opds_server.dart';

/// Exception thrown when KOReader sync authentication fails (401).
class KoreaderSyncAuthException implements Exception {
  final String message;
  KoreaderSyncAuthException([this.message = 'Authentication failed']);

  @override
  String toString() => 'KoreaderSyncAuthException: $message';
}

/// Service for interacting with a KOReader-compatible sync server.
///
/// The KOReader sync protocol uses:
/// - Custom headers `x-auth-user` and `x-auth-key` for authentication
/// - MD5 hashes as document identifiers
/// - API versioning via Accept header (`application/vnd.koreader.v1+json`)
class KoreaderSyncService {
  final OPDSServer _server;
  final Dio _dio;

  static const String _deviceIdKey = 'koreader_sync_device_id';
  static const String _deviceName = 'Worldhopper';

  KoreaderSyncService(this._server) : _dio = _createClient(_server);

  static Dio _createClient(OPDSServer server) {
    final baseUrl = server.koreaderSyncUrl ?? '';

    final dio = Dio(
      BaseOptions(
        baseUrl: baseUrl,
        connectTimeout: const Duration(seconds: 15),
        receiveTimeout: const Duration(seconds: 15),
        headers: {
          'Accept': 'application/vnd.koreader.v1+json',
          'Content-Type': 'application/json',
        },
      ),
    );

    // Add KOReader auth headers
    final username = server.koreaderSyncUsername;
    final password = server.koreaderSyncPassword;

    if (username != null &&
        username.isNotEmpty &&
        password != null &&
        password.isNotEmpty) {
      // KOReader clients send the MD5 of the password as x-auth-key
      final hashedPassword = md5.convert(utf8.encode(password)).toString();

      dio.interceptors.add(
        InterceptorsWrapper(
          onRequest: (options, handler) {
            options.headers['x-auth-user'] = username;
            options.headers['x-auth-key'] = hashedPassword;
            return handler.next(options);
          },
        ),
      );
    }

    return dio;
  }

  /// Test authentication against the sync server.
  /// Returns `true` if credentials are valid.
  /// Also serves as a connectivity check — a connection error means
  /// the server is unreachable, while a 401 means bad credentials.
  Future<bool> authenticate() async {
    try {
      final response = await _dio.get('/users/auth');
      return response.statusCode == 200;
    } on DioException catch (e) {
      if (e.response?.statusCode == 401) {
        return false;
      }
      rethrow;
    }
  }

  /// Register a new user on the sync server.
  /// Returns `true` if registration succeeded.
  /// Throws if the server has registration disabled or user already exists.
  Future<bool> registerUser() async {
    try {
      final response = await _dio.post(
        '/users/create',
        data: {
          'username': _server.koreaderSyncUsername,
          'password': md5
              .convert(utf8.encode(_server.koreaderSyncPassword ?? ''))
              .toString(),
        },
      );
      return response.statusCode == 201;
    } on DioException catch (e) {
      debugPrint('KOReader sync registration failed: ${e.message}');
      rethrow;
    }
  }

  /// Get reading progress for a document.
  /// [documentHash] is the MD5 hash identifying the document.
  /// Returns `null` if no progress is stored for this document.
  Future<KoreaderProgress?> getProgress(String documentHash) async {
    try {
      final response = await _dio.get('/syncs/progress/$documentHash');

      if (response.statusCode == 200 && response.data is Map) {
        final data = response.data as Map<String, dynamic>;
        // Empty response means no progress stored
        if (data.isEmpty) return null;
        // Response without document field means no real progress
        if (!data.containsKey('document')) return null;
        return KoreaderProgress.fromJson(data);
      }
      return null;
    } on DioException catch (e) {
      if (e.response?.statusCode == 401) {
        throw KoreaderSyncAuthException();
      }
      debugPrint('KOReader sync getProgress error: ${e.message}');
      return null;
    }
  }

  /// Update reading progress for a document.
  /// Returns `true` if the update was successful.
  Future<bool> updateProgress({
    required String documentHash,
    required double percentage,
    required String progress,
    String? device,
    String? deviceId,
  }) async {
    try {
      final resolvedDeviceId = deviceId ?? await _getDeviceId();
      final response = await _dio.put(
        '/syncs/progress',
        data: {
          'document': documentHash,
          'percentage': percentage,
          'progress': progress,
          'device': device ?? _deviceName,
          'device_id': resolvedDeviceId,
        },
      );
      return response.statusCode == 200;
    } on DioException catch (e) {
      if (e.response?.statusCode == 401) {
        throw KoreaderSyncAuthException();
      }
      debugPrint('KOReader sync updateProgress error: ${e.message}');
      return false;
    }
  }

  /// Compute the partial MD5 hash of a file, matching KOReader's algorithm.
  ///
  /// KOReader uses a non-uniform sampling strategy: it reads 1024-byte chunks
  /// at exponentially increasing offsets (0, 1024, 4096, 16384, …). This
  /// ensures the hash is dominated by the file head and is resilient to data
  /// appended at the tail (e.g. PDF highlight annotations).
  ///
  /// See `util.partialMD5` in KOReader source.
  static Future<String> computeFileHash(File file) async {
    const int step = 1024;
    const int size = 1024;

    // Offsets sampled by KOReader's partialMD5:
    //   i = -1  →  lshift(1024, -2) overflows 32-bit → 0
    //   i =  0  →  1024
    //   i =  1  →  4096
    //   ...
    //   i = 10  →  1073741824
    final offsets = <int>[
      0, // i = -1 (LuaJIT 32-bit overflow gives 0)
      for (int i = 0; i <= 10; i++) step << (2 * i),
    ];

    final raf = await file.open(mode: FileMode.read);
    try {
      final samples = <int>[];
      for (final offset in offsets) {
        await raf.setPosition(offset);
        final chunk = await raf.read(size);
        if (chunk.isEmpty) break;
        samples.addAll(chunk);
      }
      return md5.convert(samples).toString();
    } finally {
      await raf.close();
    }
  }

  /// Compute MD5 hash from a string (e.g., entry ID) for document identification.
  /// Used as a fallback when the actual file is not available.
  static String computeStringHash(String input) {
    return md5.convert(utf8.encode(input)).toString();
  }

  /// Get or create a persistent device ID for this app installation.
  static Future<String> _getDeviceId() async {
    final prefs = await SharedPreferences.getInstance();
    var deviceId = prefs.getString(_deviceIdKey);
    if (deviceId == null) {
      deviceId = const Uuid().v4();
      await prefs.setString(_deviceIdKey, deviceId);
    }
    return deviceId;
  }

  /// Get the device ID (public accessor for use in providers).
  static Future<String> getDeviceId() => _getDeviceId();
}