import 'package:flutter/foundation.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:shared_preferences/shared_preferences.dart';

const _prefsKey = 'api_base_url';

/// Backend origin when the user has not chosen one. Override at build time:
/// `flutter run --dart-define=API_BASE_URL=https://fin.example.com`.
/// On web the default is the page's own origin (Caddy serves app and API together).
String defaultApiBaseUrl() {
  const fromEnv = String.fromEnvironment('API_BASE_URL');
  if (fromEnv.isNotEmpty) return fromEnv;
  if (kIsWeb) return Uri.base.origin;
  return 'http://127.0.0.1:8000';
}

/// The address saved on this device, read in `main()` before `runApp`. Loading it up front,
/// rather than lazily like the theme, matters: the session restore fires a request on
/// startup and it must already go to the right server.
Future<String?> loadStoredApiBaseUrl() async =>
    (await SharedPreferences.getInstance()).getString(_prefsKey);

/// Overridden in `main()` with [loadStoredApiBaseUrl]; null (tests, nothing saved) means default.
final initialApiBaseUrlProvider = Provider<String?>((_) => null);

/// Backend origin every client is built against. Watched by `apiProvider` and
/// `authDioProvider`, so changing it rebuilds them. To switch servers use
/// `switchApiBaseUrl`: tokens and cached data belong to the old one.
final apiBaseUrlProvider = NotifierProvider<ApiBaseUrlController, String>(
  ApiBaseUrlController.new,
);

class ApiBaseUrlController extends Notifier<String> {
  @override
  String build() => ref.watch(initialApiBaseUrlProvider) ?? defaultApiBaseUrl();

  /// [input] as an origin-like URL without a trailing slash, or null if it is not an
  /// absolute http(s) URL.
  static String? normalize(String input) {
    final uri = Uri.tryParse(input.trim());
    if (uri == null || !uri.hasAuthority || uri.host.isEmpty) return null;
    if (uri.scheme != 'http' && uri.scheme != 'https') return null;
    final s = uri.toString();
    return s.endsWith('/') ? s.substring(0, s.length - 1) : s;
  }

  /// Persists [url]; null goes back to [defaultApiBaseUrl].
  Future<void> save(String? url) async {
    final prefs = await SharedPreferences.getInstance();
    if (url == null) {
      await prefs.remove(_prefsKey);
      state = defaultApiBaseUrl();
    } else {
      await prefs.setString(_prefsKey, url);
      state = url;
    }
  }
}