export interface ApiEnvelope<T> {
  code: string;
  message: string;
  data: T;
  requestId: string;
}
export interface ApiFailure {
  code: string;
  message: string;
  status: number | undefined;
  requestId: string | undefined;
}
export interface ApiClientOptions {
  fetcher?: typeof fetch;
  baseUrl?: string;
  getToken: () => string | null;
  setToken: (token: string | null) => void;
  onUnauthorized?: () => void;
}

export class ApiError extends Error implements ApiFailure {
  public status: number | undefined;
  public requestId: string | undefined;
  constructor(
    public code: string,
    message: string,
    status?: number,
    requestId?: string,
  ) {
    super(message);
    this.status = status;
    this.requestId = requestId;
  }
}

export function createApiClient(options: ApiClientOptions) {
  const fetcher = options.fetcher ?? fetch;
  const baseUrl = options.baseUrl ?? "/api/v1";
  let refreshing: Promise<string> | null = null;
  let failedRefresh: { token: string | null; error: unknown } | null = null;

  async function refresh(
    staleToken: string | null = options.getToken(),
  ): Promise<string> {
    // 同一认证失败周期内:只要令牌仍是失败时的令牌(或已被清空),
    // 就直接抛出已记录的失败,不再请求 refresh 接口或重复触发登出。
    if (
      failedRefresh !== null &&
      (staleToken === failedRefresh.token || staleToken === null)
    )
      throw failedRefresh.error;
    if (!refreshing) {
      refreshing = (async () => {
        try {
          const response = await fetcher(`${baseUrl}/auth/token/refresh`, {
            method: "POST",
            credentials: "include",
          });
          const body = (await response.json()) as ApiEnvelope<{
            accessToken: string;
          }>;
          if (!response.ok)
            throw new ApiError(
              body.code,
              body.message,
              response.status,
              body.requestId,
            );
          options.setToken(body.data.accessToken);
          failedRefresh = null;
          return body.data.accessToken;
        } catch (error) {
          const failure = networkError(error);
          failedRefresh = { token: staleToken, error: failure };
          options.setToken(null);
          options.onUnauthorized?.();
          throw failure;
        } finally {
          refreshing = null;
        }
      })();
    }
    return refreshing;
  }

  async function request<T>(
    path: string,
    init: RequestInit = {},
    retry = true,
  ): Promise<T> {
    const headers = new Headers(init.headers);
    const token = options.getToken();
    if (token) headers.set("authorization", `Bearer ${token}`);
    if (init.body && !headers.has("content-type"))
      headers.set("content-type", "application/json");
    let response: Response;
    try {
      response = await fetcher(`${baseUrl}${path}`, {
        ...init,
        headers,
        credentials: "include",
      });
    } catch (error) {
      throw networkError(error);
    }
    const body = (await response.json()) as ApiEnvelope<T>;
    if (response.status === 401 && retry && path !== "/auth/token/refresh") {
      await refresh(token);
      return request<T>(path, init, false);
    }
    if (!response.ok)
      throw new ApiError(
        body.code,
        body.message,
        response.status,
        body.requestId,
      );
    return body.data;
  }
  return {
    get: <T>(path: string) => request<T>(path),
    post: <T>(path: string, body?: unknown, headers?: HeadersInit) =>
      request<T>(path, {
        method: "POST",
        ...(body === undefined ? {} : { body: JSON.stringify(body) }),
        ...(headers === undefined ? {} : { headers }),
      }),
    put: <T>(path: string, body: unknown) =>
      request<T>(path, { method: "PUT", body: JSON.stringify(body) }),
    patch: <T>(path: string, body: unknown) =>
      request<T>(path, { method: "PATCH", body: JSON.stringify(body) }),
    delete: <T>(path: string) => request<T>(path, { method: "DELETE" }),
    refresh,
  };
}
function networkError(error: unknown): ApiError {
  if (error instanceof ApiError) return error;
  return new ApiError(
    "NETWORK_ERROR",
    error instanceof Error ? error.message : "网络连接失败",
  );
}