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

import 'package:crypto/crypto.dart';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter_secure_storage/flutter_secure_storage.dart';
import 'package:shared_preferences/shared_preferences.dart';

import '../push/push_secure_storage.dart';

class AccountData {
  static const _usernameField = 'username';
  static const _passwordField = 'password';
  // App password lives in the push-shared (group-scoped) keystore so the iOS
  // Notification Service Extension can authenticate Nextcloud calls too.
  static const _appPasswordField = 'nextcloud_app_password';

  static const FlutterSecureStorage _secureStorage = FlutterSecureStorage();

  static final AccountData _instance = AccountData._construct();
  Completer<void> _populated = Completer();

  factory AccountData() => _instance;

  AccountData._construct() {
    _migrateAndLoad();
  }

  String? _username;
  String? _password;
  String? _appPassword;

  String getUsername() {
    if (_username == null) throw Exception('Username not initialized');
    return _username!;
  }

  String getPassword() {
    if (_password == null) throw Exception('Password not initialized');
    return _password!;
  }

  String getUserSecret() => sha512
      .convert(utf8.encode('${getUsername()}:${getPassword()}'))
      .toString();

  Future<String> getDeviceId() async => sha512
      .convert(
        utf8.encode(
          '${getUserSecret()}@${await FirebaseMessaging.instance.getToken()}',
        ),
      )
      .toString();

  Future<void> setData(String username, String password) async {
    await _secureStorage.write(key: _usernameField, value: username);
    await _secureStorage.write(key: _passwordField, value: password);
    _username = username;
    _password = password;
    if (!_populated.isCompleted) _populated.complete();
  }

  Future<void> removeData() async {
    _populated = Completer();
    _username = null;
    _password = null;
    _appPassword = null;
    await _secureStorage.delete(key: _usernameField);
    await _secureStorage.delete(key: _passwordField);
    await _clearAppPasswordStorage();
  }

  /// Persists a freshly minted Nextcloud app password. After this every
  /// [getBasicAuthHeader] call authenticates with the app password instead of
  /// the real password.
  Future<void> setAppPassword(String appPassword) async {
    _appPassword = appPassword;
    try {
      await pushSecureStorage.write(key: _appPasswordField, value: appPassword);
    } on Object {
      // Group-scoped keystore may be unavailable (e.g. iOS entitlement not yet
      // provisioned). Keeping it in memory still lets this session use it.
    }
  }

  Future<void> clearAppPassword() async {
    _appPassword = null;
    await _clearAppPasswordStorage();
  }

  bool hasAppPassword() => _appPassword != null && _appPassword!.isNotEmpty;

  Future<void> _clearAppPasswordStorage() async {
    try {
      await pushSecureStorage.delete(key: _appPasswordField);
    } on Object {
      // ignore — nothing stored or keystore unavailable
    }
  }

  Future<void> _migrateAndLoad() async {
    await _migrateFromLegacyStorage();
    _username = await _secureStorage.read(key: _usernameField);
    _password = await _secureStorage.read(key: _passwordField);
    try {
      _appPassword = await pushSecureStorage.read(key: _appPasswordField);
    } on Object {
      _appPassword = null;
    }
    if (!_populated.isCompleted) _populated.complete();
  }

  // Move credentials from the old SharedPreferences plain-text storage into the
  // platform's secure keystore. Run once per install and clear the legacy keys.
  Future<void> _migrateFromLegacyStorage() async {
    final prefs = await SharedPreferences.getInstance();
    final legacyUsername = prefs.getString(_usernameField);
    final legacyPassword = prefs.getString(_passwordField);
    if (legacyUsername == null || legacyPassword == null) return;

    final hasSecure = (await _secureStorage.read(key: _usernameField)) != null;
    if (!hasSecure) {
      await _secureStorage.write(key: _usernameField, value: legacyUsername);
      await _secureStorage.write(key: _passwordField, value: legacyPassword);
    }
    await prefs.remove(_usernameField);
    await prefs.remove(_passwordField);
  }

  Future<bool> waitForPopulation() async {
    await _populated.future;
    return isPopulated();
  }

  bool isPopulated() => _username != null && _password != null;

  /// Returns the value for an HTTP `Authorization` header using HTTP Basic.
  /// Prefer this over embedding credentials in URLs — error logs and crash
  /// reports often capture the URL but not headers.
  String getBasicAuthHeader() {
    if (!isPopulated()) {
      throw Exception(
        'AccountData (e.g. username or password) is not initialized!',
      );
    }
    // Prefer the scoped app password once available; it survives real-password
    // rotation and is what the push-v2 registration is bound to.
    final secret = _appPassword ?? _password;
    return 'Basic ${base64Encode(utf8.encode('$_username:$secret'))}';
  }

  /// Basic-auth header that always uses the real password. Needed exactly once,
  /// to mint the app password via `core/getapppassword` (an app password cannot
  /// mint another).
  String getRealPasswordBasicAuthHeader() {
    if (!isPopulated()) {
      throw Exception(
        'AccountData (e.g. username or password) is not initialized!',
      );
    }
    return 'Basic ${base64Encode(utf8.encode('$_username:$_password'))}';
  }

  /// Convenience wrapper around [getBasicAuthHeader] returning a single-entry
  /// header map ready to merge into HTTP request headers.
  Map<String, String> authHeaders() => {'Authorization': getBasicAuthHeader()};
}