// http.ts — HttpClient：真实后端薄客户端（阶段 B 联调）。
// 特性：API 域名池(故障转移) + 指数退避重试 + 统一错误体解析 + 静默续期。
import {
  ApiClient,
  ApiError,
  ApiErrorBody,
  Device,
  LoginResult,
  Me,
  RedeemResult,
  Session,
  SubscriptionInfo,
  TotpSetup,
} from './types';
import {
  accessValid,
  clearSession,
  getAccessToken,
  getRefreshToken,
  setSession,
} from './session';

function domains(): string[] {
  const raw = process.env.NEXT_PUBLIC_API_DOMAINS || '';
  const list = raw.split(',').map((s) => s.trim()).filter(Boolean);
  return list.length ? list : ['/api'];
}

const sleep = (ms: number) => new Promise((r) => setTimeout(r, ms));

interface ReqOpts {
  method?: string;
  body?: unknown;
  auth?: boolean;
  /** 401 时是否尝试静默续期后重放(默认 true,refresh 自身置 false 防递归) */
  allowRefresh?: boolean;
  refreshToken?: string;
}

export class HttpClient implements ApiClient {
  private refreshing: Promise<Session> | null = null;

  /** 跨域名池 + 退避的核心请求 */
  private async request<T>(path: string, opts: ReqOpts = {}): Promise<T> {
    const { method = 'GET', body, auth = true, allowRefresh = true } = opts;

    if (auth && !accessValid() && getRefreshToken()) {
      await this.ensureFresh();
    }

    const pool = domains();
    let lastErr: unknown;

    for (let attempt = 0; attempt < pool.length * 2; attempt++) {
      const base = pool[attempt % pool.length];
      try {
        const headers: Record<string, string> = { Accept: 'application/json' };
        if (body !== undefined) headers['Content-Type'] = 'application/json';
        const token = getAccessToken();
        if (auth && token) headers['Authorization'] = `Bearer ${token}`;
        if (opts.refreshToken) headers['X-Refresh-Token'] = opts.refreshToken;

        const res = await fetch(base + path, {
          method,
          headers,
          body: body !== undefined ? JSON.stringify(body) : undefined,
          credentials: 'omit',
        });

        if (res.status === 401 && auth && allowRefresh && getRefreshToken()) {
          await this.ensureFresh(true);
          // 续期后重放一次（不再允许二次续期）
          return this.request<T>(path, { ...opts, allowRefresh: false });
        }

        if (!res.ok) throw await this.toApiError(res);
        if (res.status === 204) return undefined as T;
        return (await res.json()) as T;
      } catch (err) {
        lastErr = err;
        // 业务错误(ApiError)不重试;仅网络/5xx 才退避换域名
        if (err instanceof ApiError && err.code !== 'network') throw err;
        await sleep(Math.min(1000 * 2 ** attempt, 4000));
      }
    }
    throw lastErr instanceof ApiError
      ? lastErr
      : new ApiError({ code: 'network', message_zh: '网络异常,请稍后重试', message_en: 'Network error, please retry' });
  }

  private async toApiError(res: Response): Promise<ApiError> {
    let bodyJson: Partial<ApiErrorBody> = {};
    try {
      bodyJson = await res.json();
    } catch {
      /* non-json error */
    }
    const code = bodyJson.code || (res.status === 401 ? 'unauthorized' : 'unknown');
    const retryAfter = Number(res.headers.get('Retry-After')) || undefined;
    return new ApiError(
      {
        code,
        message_zh: bodyJson.message_zh || '',
        message_en: bodyJson.message_en || '',
      },
      retryAfter,
    );
  }

  private ensureFresh(force = false): Promise<Session> {
    if (!force && accessValid()) return Promise.resolve(null as unknown as Session);
    if (this.refreshing) return this.refreshing;
    this.refreshing = this.refresh().finally(() => {
      this.refreshing = null;
    });
    return this.refreshing;
  }

  async login(email: string, password: string): Promise<LoginResult> {
    const r = await this.request<
      { kind: 'session'; session: Session } | { kind: 'totp_required'; pending_token: string }
    >('/v1/auth/login', { method: 'POST', body: { email, password }, auth: false });
    if ('pending_token' in r) return { kind: 'totp_required', pendingToken: r.pending_token };
    setSession(r.session);
    return r;
  }

  async loginTotp(pendingToken: string, code: string): Promise<Session> {
    const s = await this.request<Session>('/v1/auth/login/totp', {
      method: 'POST',
      body: { pending_token: pendingToken, code },
      auth: false,
    });
    setSession(s);
    return s;
  }

  async refresh(): Promise<Session> {
    const rt = getRefreshToken();
    if (!rt) throw new ApiError({ code: 'unauthorized', message_zh: '登录已失效', message_en: 'Session expired' });
    const s = await this.request<Session>('/v1/auth/refresh', {
      method: 'POST',
      auth: false,
      allowRefresh: false,
      refreshToken: rt,
    });
    setSession(s);
    return s;
  }

  getMe = () => this.request<Me>('/v1/me');
  getSubscription = () => this.request<SubscriptionInfo>('/v1/me/subscription');
  resetSubscription = () => this.request<SubscriptionInfo>('/v1/me/subscription/reset', { method: 'POST' });
  listDevices = () => this.request<Device[]>('/v1/me/devices');
  removeDevice = (id: string) => this.request<void>(`/v1/me/devices/${encodeURIComponent(id)}`, { method: 'DELETE' });
  redeem = (code: string) => this.request<RedeemResult>('/v1/me/redeem', { method: 'POST', body: { code } });

  // 契约增补待 #1 合入：POST /v1/me/totp/setup|verify|disable
  totpSetup = () => this.request<TotpSetup>('/v1/me/totp/setup', { method: 'POST' });
  totpVerify = (code: string) => this.request<void>('/v1/me/totp/verify', { method: 'POST', body: { code } });
  totpDisable = (code: string) => this.request<void>('/v1/me/totp/disable', { method: 'POST', body: { code } });

  async logout(): Promise<void> {
    try {
      await this.request<void>('/v1/auth/logout', { method: 'POST' });
    } finally {
      clearSession();
    }
  }
}