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

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

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

  final double quote;
  final double result;
}

class FrankfurterApiService {
  FrankfurterApiService({required this.httpClient});

  final http.Client httpClient;

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

  String _redactedUri(Uri uri) => uri.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 statusCode = error?['statusCode']?.toString();
      return statusCode == '429';
    } catch (_) {
      return false;
    }
  }

  DateTime _asUtcDate(DateTime value) {
    return DateTime.utc(value.year, value.month, value.day);
  }

  DateTime _todayUtcDate() {
    final nowUtc = DateTime.now().toUtc();
    return DateTime.utc(nowUtc.year, nowUtc.month, nowUtc.day);
  }

  DateTime _normalizeHistoricalDate(DateTime requestedDate) {
    final requestedUtcDate = _asUtcDate(requestedDate);
    final latestAllowed = _todayUtcDate();
    if (requestedUtcDate.isAfter(latestAllowed)) {
      _log(
        'Requested date ${DateFormat('yyyy-MM-dd').format(requestedUtcDate)} is in the future; clamping to ${DateFormat('yyyy-MM-dd').format(latestAllowed)}.',
      );
      return latestAllowed;
    }
    return requestedUtcDate;
  }

  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 {
    final effectiveDate = _normalizeHistoricalDate(estDate);
    final date = DateFormat('yyyy-MM-dd').format(effectiveDate);
    final uri = Uri.https('api.frankfurter.dev', '/v1/$date', <String, String>{
      'base': 'USD',
      'symbols': 'SEK',
    });

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

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

    final json = jsonDecode(response.body) as Map<String, dynamic>;
    final rates = json['rates'] as Map<String, dynamic>?;
    final sek = rates?['SEK'];
    if (sek == null) {
      throw StateError('SEK rate was missing in Frankfurter response.');
    }

    _log('Daily rate parsed SEK quote: $sek');

    return (sek as num).toDouble();
  }

  Future<ConversionResult> convertUsdToSek({
    required DateTime estDate,
    required double amount,
  }) async {
    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 ConversionResult(quote: quote, result: result);
  }

  /// Fetches USD->SEK cross-rates for [year] using Frankfurter's date-range
  /// endpoint. Returns a map of 'yyyy-MM-dd' -> rate.
  Future<Map<String, double>?> tryFetchYearRates(int year) async {
    final start = DateTime(year, 1, 1);
    final end = DateTime(year, 12, 31);
    final rangePath =
        '/v1/${DateFormat('yyyy-MM-dd').format(start)}..${DateFormat('yyyy-MM-dd').format(end)}';
    final uri = Uri.https('api.frankfurter.dev', rangePath, <String, String>{
      'base': 'USD',
      'symbols': 'SEK',
    });

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

    final response = await _getWithRateLimitRetry(uri, operation: 'Range');
    if (response.statusCode != 200) {
      _log(
        'Range endpoint unavailable; falling back to per-day requests. status=${response.statusCode}',
      );
      return null;
    }

    final json = jsonDecode(response.body) as Map<String, dynamic>;
    final rates = json['rates'] as Map<String, dynamic>?;
    if (rates == null) {
      _log('Range response missing rates; falling back to per-day requests.');
      return null;
    }

    final results = <String, double>{};
    for (final entry in rates.entries) {
      final dayRates = entry.value as Map<String, dynamic>?;
      final sek = dayRates?['SEK'];
      if (sek is num) {
        results[entry.key] = sek.toDouble();
      }
    }

    if (results.isEmpty) {
      _log('Range parsed no SEK entries; falling back to per-day requests.');
      return null;
    }

    _log('Range parsed ${results.length} daily SEK quotes.');
    return results;
  }
}