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

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

class ForexConversionResult {
  ForexConversionResult({required this.quote, required this.result});

  final double quote;
  final double result;
}

class ForexRateApiService {
  ForexRateApiService({required this.httpClient, required this.apiKey});

  final http.Client httpClient;
  final String apiKey;

  void _log(String message) {
    if (kDebugMode) {
      debugPrint('[ForexRateApiService] $message');
    }
  }

  String _redactedUri(Uri uri) {
    final redactedQuery = <String, String>{...uri.queryParameters};
    if (redactedQuery.containsKey('access_key')) {
      redactedQuery['access_key'] = '***REDACTED***';
    }
    return uri.replace(queryParameters: redactedQuery).toString();
  }

  bool _isRateLimitedResponse(http.Response response) {
    if (response.statusCode == 429) {
      return true;
    }

    try {
      final parsed = jsonDecode(response.body) as Map<String, dynamic>;
      final error = parsed['error'] as Map<String, dynamic>?;
      final code = error?['code']?.toString().toLowerCase();
      return code == 'rate_limit_reached';
    } catch (_) {
      return false;
    }
  }

  Future<http.Response> _getWithRateLimitRetry(
    Uri uri, {
    required String operation,
  }) async {
    const maxAttempts = 3;

    for (var attempt = 1; attempt <= maxAttempts; attempt++) {
      final response = await httpClient.get(uri);
      _log('$operation HTTP status: ${response.statusCode}');
      _log('$operation raw response: ${response.body}');

      final shouldRetry = _isRateLimitedResponse(response);
      if (!shouldRetry || attempt == maxAttempts) {
        return response;
      }

      final delayMs = 1200 * attempt;
      _log(
        '$operation rate limited; retrying in ${delayMs}ms (attempt ${attempt + 1}/$maxAttempts)',
      );
      await Future.delayed(Duration(milliseconds: delayMs));
    }

    throw StateError('Unexpected rate-limit retry flow for $operation.');
  }

  Future<double> fetchUsdToSekRate({required DateTime estDate}) async {
    if (apiKey == 'REPLACE_WITH_YOUR_EXCHANGE_RATE_API_KEY') {
      throw StateError('ExchangeratesAPI key is not configured.');
    }

    final date = DateFormat('yyyy-MM-dd').format(estDate);
    final uri = Uri.https(
      'api.exchangeratesapi.io',
      '/v1/$date',
      // Free-tier plans can restrict custom base currencies.
      // We request EUR-based USD and SEK rates and derive USD->SEK via cross-rate.
      <String, String>{'access_key': apiKey, 'symbols': 'USD,SEK'},
    );

    _log('Daily rate request: ${_redactedUri(uri)}');

    final response = await _getWithRateLimitRetry(uri, operation: 'Daily rate');
    if (response.statusCode != 200) {
      throw StateError(
        'ExchangeratesAPI request failed (${response.statusCode}).',
      );
    }

    final json = jsonDecode(response.body) as Map<String, dynamic>;
    final success = json['success'] as bool? ?? false;
    if (!success) {
      final error = json['error'];
      _log('Daily rate success=false. error=$error');
      throw StateError('ExchangeratesAPI returned success=false. error=$error');
    }

    final rates = json['rates'] as Map<String, dynamic>?;
    final usdPerEur = rates?['USD'];
    final sekPerEur = rates?['SEK'];
    if (usdPerEur == null || sekPerEur == null) {
      throw StateError('USD/SEK rates were missing in API response.');
    }

    final usdPerEurValue = (usdPerEur as num).toDouble();
    final sekPerEurValue = (sekPerEur as num).toDouble();
    if (usdPerEurValue == 0) {
      throw StateError('USD rate was zero; cannot derive USD->SEK.');
    }

    final usdToSek = sekPerEurValue / usdPerEurValue;

    _log(
      'Daily rate parsed usdPerEur=$usdPerEurValue sekPerEur=$sekPerEurValue derivedUsdToSek=$usdToSek',
    );

    return usdToSek;
  }

  Future<ForexConversionResult> convertUsdToSek({
    required DateTime estDate,
    required double amount,
  }) async {
    if (apiKey == 'REPLACE_WITH_YOUR_EXCHANGE_RATE_API_KEY') {
      throw StateError('ExchangeratesAPI key is not configured.');
    }

    final quote = await fetchUsdToSekRate(estDate: estDate);
    final result = quote * amount;

    _log(
      'Computed conversion from daily rate quote=$quote result=$result amount=$amount date=${DateFormat('yyyy-MM-dd').format(estDate)}',
    );

    return ForexConversionResult(quote: quote, result: result);
  }
}