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._();

  /// 真机默认使用的开发机局域网地址。
  ///
  /// 这个地址跟着电脑所在的网络走，换网络后要用
  /// `ipconfig getifaddr en0` 重新确认。默认值只改这一行。
  static const String devHostBaseUrl = 'http://192.168.31.187:8081';

  static const String _loopbackBaseUrl = 'http://127.0.0.1:8081';

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

  static String _runtimeBaseUrl = '';

  /// 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
      ? _loopbackBaseUrl
      : 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);

  /// 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';
  }
}