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

import 'package:flutter/services.dart';
import 'package:http/http.dart' as http;

final class RemoteConnectionsService {
  const RemoteConnectionsService({http.Client? client}) : _client = client;

  static Future<String>? _cachedEndpoint;

  final http.Client? _client;

  Future<List<String>> fetchConfigLinks() async {
    final Uri uri = await _connectionsUri();

    final http.Client client = _client ?? http.Client();

    try {
      final http.Response response = await client
          .get(
            uri,
            headers: const <String, String>{'accept': 'application/json'},
          )
          .timeout(const Duration(seconds: 15));

      if (response.statusCode != 200) {
        throw RemoteConnectionsException(
          'Remote server returned ${response.statusCode} for GET /connections',
        );
      }

      final dynamic decoded = jsonDecode(response.body);
      final List<String> links = _extractLinks(decoded);
      return links.toSet().toList();
    } on TimeoutException {
      throw const RemoteConnectionsException('Remote request timeout');
    } on FormatException {
      throw const RemoteConnectionsException(
        'Remote response is not valid JSON',
      );
    } finally {
      if (_client == null) {
        client.close();
      }
    }
  }

  Future<void> addConfigLink(String link) async {
    final String normalized = link.trim();
    if (normalized.isEmpty) {
      throw const RemoteConnectionsException('Config link is empty');
    }

    final Uri uri = await _connectionsUri();
    final http.Client client = _client ?? http.Client();

    try {
      final http.Response response = await client
          .post(
            uri,
            headers: const <String, String>{
              'accept': 'application/json',
              'content-type': 'application/json',
            },
            body: jsonEncode(<String, String>{'url': normalized}),
          )
          .timeout(const Duration(seconds: 15));

      if (response.statusCode == 201) {
        return;
      }

      if (response.statusCode == 409) {
        throw const RemoteConnectionsException('Remote link already exists');
      }

      if (response.statusCode == 400) {
        throw const RemoteConnectionsException(
          'Remote server rejected payload',
        );
      }

      throw RemoteConnectionsException(
        'Remote server returned ${response.statusCode} for POST /connections',
      );
    } on TimeoutException {
      throw const RemoteConnectionsException('Remote request timeout');
    } finally {
      if (_client == null) {
        client.close();
      }
    }
  }

  Future<void> deleteConfigLink(String link) async {
    final String normalized = link.trim();
    if (normalized.isEmpty) {
      throw const RemoteConnectionsException('Config link is empty');
    }

    final Uri uri = await _connectionsUri();
    final http.Client client = _client ?? http.Client();

    try {
      final http.Response response = await client
          .delete(
            uri,
            headers: const <String, String>{
              'accept': 'application/json',
              'content-type': 'application/json',
            },
            body: jsonEncode(<String, String>{'url': normalized}),
          )
          .timeout(const Duration(seconds: 15));

      if (response.statusCode == 200) {
        return;
      }

      if (response.statusCode == 404) {
        throw const RemoteConnectionsException('Remote link not found');
      }

      if (response.statusCode == 400) {
        throw const RemoteConnectionsException(
          'Remote server rejected payload',
        );
      }

      throw RemoteConnectionsException(
        'Remote server returned ${response.statusCode} for DELETE /connections',
      );
    } on TimeoutException {
      throw const RemoteConnectionsException('Remote request timeout');
    } finally {
      if (_client == null) {
        client.close();
      }
    }
  }

  Future<Uri> _connectionsUri() async {
    final String endpoint = (await _getEndpoint()).trim();
    if (endpoint.isEmpty) {
      throw const RemoteConnectionsException(
        'REMOTE_CONFIGS_URL is not configured in assets/env',
      );
    }

    final Uri uri;
    try {
      uri = Uri.parse(endpoint);
    } catch (_) {
      throw RemoteConnectionsException(
        'Invalid REMOTE_CONFIGS_URL in assets/env: $endpoint',
      );
    }

    final String normalizedPath;
    if (uri.path.isEmpty || uri.path == '/') {
      normalizedPath = '/connections';
    } else {
      normalizedPath = uri.path;
    }

    return uri.replace(path: normalizedPath);
  }

  Future<String> _getEndpoint() {
    return _cachedEndpoint ??= _loadEndpoint();
  }

  Future<String> _loadEndpoint() async {
    final String content;
    try {
      content = await rootBundle.loadString('assets/env');
    } catch (_) {
      throw const RemoteConnectionsException('Failed to load assets/env');
    }

    final Map<String, String> env = _parseEnv(content);
    return env['REMOTE_CONFIGS_URL'] ?? '';
  }

  Map<String, String> _parseEnv(String source) {
    final Map<String, String> values = <String, String>{};
    final List<String> lines = const LineSplitter().convert(source);

    for (final String line in lines) {
      final String trimmed = line.trim();
      if (trimmed.isEmpty || trimmed.startsWith('#')) {
        continue;
      }

      final int separator = trimmed.indexOf('=');
      if (separator <= 0) {
        continue;
      }

      final String key = trimmed.substring(0, separator).trim();
      String value = trimmed.substring(separator + 1).trim();

      if (value.length >= 2) {
        final bool quotedWithDouble =
            value.startsWith('"') && value.endsWith('"');
        final bool quotedWithSingle =
            value.startsWith("'") && value.endsWith("'");
        if (quotedWithDouble || quotedWithSingle) {
          value = value.substring(1, value.length - 1);
        }
      }

      if (key.isNotEmpty) {
        values[key] = value;
      }
    }

    return values;
  }

  List<String> _extractLinks(dynamic data) {
    if (data is! Map) {
      throw const RemoteConnectionsException(
        'Invalid payload: expected {"links": ["..."]}',
      );
    }

    final Map<String, dynamic> map = Map<String, dynamic>.from(data);
    final dynamic linksPayload = map['links'];
    if (linksPayload is! List) {
      throw const RemoteConnectionsException(
        'Invalid payload: expected {"links": ["..."]}',
      );
    }

    final List<String> links = <String>[];

    for (final dynamic item in linksPayload) {
      if (item is! String) {
        throw const RemoteConnectionsException(
          'Invalid payload: expected {"links": ["..."]}',
        );
      }

      final String link = item.trim();
      if (link.isNotEmpty) {
        links.add(link);
      }
    }

    return links;
  }
}

final class RemoteConnectionsException implements Exception {
  const RemoteConnectionsException(this.message);

  final String message;

  @override
  String toString() => message;
}