// Author: fruit.com.cn

import 'dart:io';

import 'package:flutter/foundation.dart';

/// 客户端与后端约定的运行时配置。
///
/// 接口地址优先级：运行时设置 > `--dart-define=API_BASE_URL=...` > 平台默认值。
/// 开发机的局域网地址会随网络变化，换网络后改 [devHostBaseUrl] 即可。
class AppConfig {
  const AppConfig._();

  /// 开发调试默认服务地址，当前指向本机局域网 IP。
  ///
  /// 换网络时只改这一行，地址不要带结尾斜杠。
  static const String devHostBaseUrl = 'http://192.168.31.187:8081';

  /// 本机后端地址：通过 `adb reverse tcp:8081 tcp:8081` 映射到开发机，
  /// 探测可达时 App 直连本机服务；不可达时回落到公网地址。
  static const String lanBaseUrl = 'http://127.0.0.1:8081';

  /// 公网地址（远程/移动网络访问时使用）。
  static const String publicBaseUrl = 'http://39.162.50.99:8081';

  static const String _overrideBaseUrl = String.fromEnvironment('API_BASE_URL');

  static String _runtimeBaseUrl = '';

  static Future<void>? _ready;

  /// 启动地址探测完成信号；默认已完成，避免影响既有测试与调用方。
  static Future<void> get ready => _ready ?? Future<void>.value();
  static set ready(Future<void> value) => _ready = value;

  static const Duration _probeTimeout = Duration(seconds: 2);
  static const List<String> _probeCandidates = [
    lanBaseUrl,
    devHostBaseUrl,
    if (devHostBaseUrl != publicBaseUrl) publicBaseUrl,
  ];

  /// Build-time server URL supplied through `--dart-define=API_BASE_URL`.
  static String get compiledBaseUrl => _overrideBaseUrl;

  /// Existing platform-aware fallback used when no runtime or build override exists.
  static String get defaultBaseUrl => _defaultBaseUrl;

  /// Effective server URL, including the debug-only runtime override.
  static String get apiBaseUrl => _runtimeBaseUrl.isNotEmpty
      ? _runtimeBaseUrl
      : (compiledBaseUrl.isNotEmpty ? compiledBaseUrl : defaultBaseUrl);

  static final String _defaultBaseUrl = _runsOnDevMachine
      ? lanBaseUrl
      : devHostBaseUrl;

  /// 模拟器、桌面端与开发机同机，环回地址可用；iOS 真机不满足。
  /// Android 没有等价的探测方式，统一按真机处理（模拟器用
  /// `--dart-define=API_BASE_URL=http://10.0.2.2:8081` 覆盖）。
  static final bool _runsOnDevMachine =
      kIsWeb ||
      defaultTargetPlatform == TargetPlatform.macOS ||
      defaultTargetPlatform == TargetPlatform.windows ||
      defaultTargetPlatform == TargetPlatform.linux ||
      (defaultTargetPlatform == TargetPlatform.iOS &&
          Platform.environment.containsKey('SIMULATOR_DEVICE_NAME'));

  /// Applies an already normalized runtime URL. Passing null clears it.
  static void applyRuntimeBaseUrl(String? value) {
    _runtimeBaseUrl = value ?? '';
  }

  /// Clears the in-memory runtime override, mainly for tests and restarts.
  static void clearRuntimeBaseUrl() {
    _runtimeBaseUrl = '';
  }

  static const Duration requestTimeout = Duration(seconds: 8);

  /// 按环回、开发机、公网顺序探测，写入首个返回 200 的地址。
  ///
  /// 全部不可达时使用平台默认地址，真机保留开发机地址，避免退回公网。
  static Future<void> probeAndApplyBaseUrl({
    Future<bool> Function(String baseUrl)? probe,
    String? fallbackBaseUrl,

    /// 编译期地址测试注入；未传时读取 `API_BASE_URL`。
    String? compiledOverride,
  }) async {
    final compiled = compiledOverride ?? compiledBaseUrl;
    if (compiled.isNotEmpty) {
      if (_runtimeBaseUrl.isEmpty) applyRuntimeBaseUrl(compiled);
      return;
    }
    final candidates = <String>[
      if (_runtimeBaseUrl.isNotEmpty) _runtimeBaseUrl,
      for (final candidate in _probeCandidates)
        if (candidate != _runtimeBaseUrl) candidate,
    ];
    final results = await Future.wait([
      for (final candidate in candidates)
        probe == null
            ? _probeBaseUrl(candidate)
            : _runInjectedProbe(candidate, probe),
    ]);
    for (var index = 0; index < candidates.length; index++) {
      final candidate = candidates[index];
      final result = results[index];
      if (kDebugMode) {
        final status = result.ok
            ? 'ok'
            : 'fail(${result.reason ?? 'request failed'})';
        debugPrint('[probe] $candidate -> $status');
      }
      if (result.ok) {
        applyRuntimeBaseUrl(candidate);
        return;
      }
    }
    applyRuntimeBaseUrl(fallbackBaseUrl ?? defaultBaseUrl);
  }

  static Future<_ProbeResult> _runInjectedProbe(
    String baseUrl,
    Future<bool> Function(String baseUrl) probe,
  ) async {
    try {
      return _ProbeResult(ok: await probe(baseUrl));
    } catch (error) {
      return _ProbeResult(ok: false, reason: error.toString());
    }
  }

  static Future<_ProbeResult> _probeBaseUrl(String baseUrl) async {
    final client = HttpClient()..connectionTimeout = _probeTimeout;
    try {
      return await _requestCategories(
        client,
        Uri.parse('$baseUrl/app/categories'),
      ).timeout(_probeTimeout);
    } catch (error) {
      return _ProbeResult(ok: false, reason: error.toString());
    } finally {
      client.close(force: true);
    }
  }

  static Future<_ProbeResult> _requestCategories(
    HttpClient client,
    Uri uri,
  ) async {
    final request = await client.getUrl(uri);
    final response = await request.close();
    await response.drain<void>();
    final ok = response.statusCode == 200;
    return _ProbeResult(
      ok: ok,
      reason: ok ? null : 'HTTP ${response.statusCode}',
    );
  }

  /// 后端返回的是相对路径（/files/...），这里补上服务地址。
  static String mediaUrl(String path) {
    if (path.isEmpty) return '';
    if (path.startsWith('http://') || path.startsWith('https://')) return path;
    return '$apiBaseUrl$path';
  }
}

class _ProbeResult {
  const _ProbeResult({required this.ok, this.reason});

  final bool ok;
  final String? reason;
}