import 'dart:convert';
import 'package:http/http.dart' as http;

typedef TokenProvider = String? Function();
typedef UnauthorizedHandler = Future<void> Function();

class ApiService {
  final String baseUrl;
  final http.Client _client;
  final Duration timeout;
  TokenProvider? _getToken;
  UnauthorizedHandler? _onUnauthorized;

  ApiService({
    required this.baseUrl,
    http.Client? client,
    this.timeout = const Duration(seconds: 30),
  }) : _client = client ?? http.Client();

  void setTokenProvider(TokenProvider provider) {
    _getToken = provider;
  }

  void setUnauthorizedHandler(UnauthorizedHandler handler) {
    _onUnauthorized = handler;
  }

  void dispose() {
    _client.close();
  }

  Map<String, String> _buildHeaders(Map<String, String>? extra) {
    final token = _getToken?.call();
    final headers = {'accept': 'application/json', ...?extra};
    if (token != null && token.isNotEmpty) {
      headers['Authorization'] = 'Bearer $token';
    }
    return headers;
  }

  Future<dynamic> get(String endpoint, {Map<String, String>? headers}) async {
    final response = await _client
        .get(
          Uri.parse('$baseUrl$endpoint'),
          headers: _buildHeaders(headers),
        )
        .timeout(timeout);
    return _processResponse(response);
  }

  Future<dynamic> post(
    String endpoint,
    dynamic data, {
    Map<String, String>? headers,
  }) async {
    final hasBody = data != null;
    final response = await _client
        .post(
          Uri.parse('$baseUrl$endpoint'),
          headers: _buildHeaders(hasBody ? _jsonHeaders(headers) : headers),
          body: hasBody ? jsonEncode(data) : null,
        )
        .timeout(timeout);
    return _processResponse(response);
  }

  Future<dynamic> postForm(String endpoint, Map<String, String> data) async {
    final response = await _client
        .post(
          Uri.parse('$baseUrl$endpoint'),
          headers: _buildHeaders({
            'Content-Type': 'application/x-www-form-urlencoded',
            'accept': 'application/json',
          }),
          body: data, // http package handles form-encoding for Map<String, String>
        )
        .timeout(timeout);
    return _processResponse(response);
  }

  Future<dynamic> put(
    String endpoint,
    dynamic data, {
    Map<String, String>? headers,
  }) async {
    final hasBody = data != null;
    final response = await _client
        .put(
          Uri.parse('$baseUrl$endpoint'),
          headers: _buildHeaders(hasBody ? _jsonHeaders(headers) : headers),
          body: hasBody ? jsonEncode(data) : null,
        )
        .timeout(timeout);
    return _processResponse(response);
  }

  Future<dynamic> delete(
    String endpoint, {
    Map<String, String>? headers,
  }) async {
    final response = await _client
        .delete(
          Uri.parse('$baseUrl$endpoint'),
          headers: _buildHeaders(headers),
        )
        .timeout(timeout);
    return _processResponse(response);
  }

  Map<String, String> _jsonHeaders(Map<String, String>? extra) {
    return {'Content-Type': 'application/json', if (extra != null) ...extra};
  }

  Future<dynamic> _processResponse(http.Response res) async {
    final body = _decodeBody(res);
    if (res.statusCode >= 200 && res.statusCode < 300) {
      return body;
    }

    if (res.statusCode == 401 && _onUnauthorized != null) {
      await _onUnauthorized!();
    }

    throw Exception('API error ${res.statusCode}: $body');
  }

  dynamic _decodeBody(http.Response res) {
    if (res.body.isEmpty) return null;

    final contentType = res.headers['content-type'] ?? '';
    final shouldTryJson = contentType.contains('application/json') ||
        contentType.contains('+json') ||
        res.body.trimLeft().startsWith('{') ||
        res.body.trimLeft().startsWith('[');

    if (!shouldTryJson) return res.body;

    try {
      return jsonDecode(res.body);
    } catch (_) {
      // Avoid turning a server-side error body into a client-side crash.
      return res.body;
    }
  }
}