function trimTrailingSlashes(value: string): string {
  return value.replace(/\/+$/, '');
}

export type AppVariant = 'development' | 'staging' | 'production';

const MISSING_ENV_HINT =
  'Run `npm run use-env -- <development|staging|production>` in app-expo, ' +
  'then restart Metro or re-run `expo prebuild` before building.';

/**
 * EXPO_PUBLIC_* must be set at bundle time (Metro / EAS / Xcode Archive).
 * Refuses silent fallbacks to a hard-coded LAN IP.
 */
export function requirePublicEnv(name: string): string {
  const value = process.env[name]?.trim();
  if (!value) {
    throw new Error(`[config] Missing ${name}. ${MISSING_ENV_HINT}`);
  }
  return value;
}

function parseBackendUrl(raw: string, envName: string): URL {
  let parsed: URL;
  try {
    parsed = new URL(raw);
  } catch {
    throw new Error(`[config] Invalid ${envName}: ${raw}`);
  }
  if (!parsed.protocol || parsed.protocol === ':') {
    throw new Error(`[config] ${envName} must include a scheme (http/https or ws/wss): ${raw}`);
  }
  return parsed;
}

function resolveApiBaseUrl(): string {
  const raw = requirePublicEnv('EXPO_PUBLIC_API_URL');
  const parsed = parseBackendUrl(raw, 'EXPO_PUBLIC_API_URL');
  if (parsed.protocol !== 'http:' && parsed.protocol !== 'https:') {
    throw new Error(
      `[config] EXPO_PUBLIC_API_URL must use http:// or https:// (got ${parsed.protocol})`,
    );
  }
  return trimTrailingSlashes(raw);
}

function resolveWsBaseUrl(): string {
  const raw = requirePublicEnv('EXPO_PUBLIC_WS_URL');
  const parsed = parseBackendUrl(raw, 'EXPO_PUBLIC_WS_URL');
  if (parsed.protocol !== 'ws:' && parsed.protocol !== 'wss:') {
    throw new Error(
      `[config] EXPO_PUBLIC_WS_URL must use ws:// or wss:// (got ${parsed.protocol})`,
    );
  }
  return trimTrailingSlashes(raw);
}

function resolveAppVariant(): AppVariant {
  const raw = process.env.EXPO_PUBLIC_APP_VARIANT;
  if (raw === 'development' || raw === 'staging' || raw === 'production') {
    return raw;
  }
  if (__DEV__) {
    return 'development';
  }
  // Release 包若 env 未写入 APP_VARIANT（例如仅复制了 env/staging 到 .env 但变量缺失），
  // 仍按 API 是否为 http 推断预发，避免关于页误隐藏后端地址。
  const apiUrl = process.env.EXPO_PUBLIC_API_URL ?? '';
  if (apiUrl.startsWith('http://')) {
    return 'staging';
  }
  return 'production';
}

/** Shown on About screen for dev/staging builds only (never production Release). */
export function shouldShowAboutBackendUrl(variant: AppVariant = appVariant): boolean {
  // Metro / 调试包：始终显示，避免 .env 误用 production variant 时看不到实际 API
  if (__DEV__) {
    return true;
  }
  return variant === 'development' || variant === 'staging';
}

export const appVariant = resolveAppVariant();

export const config = {
  apiBaseUrl: resolveApiBaseUrl(),
  wsBaseUrl: resolveWsBaseUrl(),
  isDebugMode: __DEV__,
  appVariant,
  showAboutBackendUrl: shouldShowAboutBackendUrl(),

  api: {
    timeoutMs: 30_000,
    refreshPath: '/api/auth/refresh',
  },

  ws: {
    reconnectMaxRetries: 10,
    reconnectBaseDelayMs: 1_000,
    reconnectMaxDelayMs: 30_000,
    heartbeatIntervalMs: 30_000,
    /**
     * 仅当 App 处于 `background` 连续超过该毫秒数才释放当前会话 WebSocket。
     * 短暂切到其它应用再返回时保持连接，避免反复重连。
     */
    backgroundDisconnectAfterMs: 300_000,
  },
} as const;