import { z } from "zod";

export const PROJECT_REQUEST_TIMEOUT_MS = 15_000;
const READINESS_TIMEOUT_MS = 3_000;
const readinessSchema = z.object({
  status: z.enum(["ready", "not_ready"]),
  checks: z.object({
    startup: z.string(),
    metadata_database: z.string(),
    mcp_transport: z.string()
  })
});

const isTimeout = (error: unknown) => Boolean(error && typeof error === "object"
  && "name" in error && error.name === "TimeoutError");

async function describeServerReadiness(baseUrl: string): Promise<string> {
  try {
    const response = await fetch(`${baseUrl}/ready`, {
      signal: AbortSignal.timeout(READINESS_TIMEOUT_MS),
      headers: { Accept: "application/json" },
      cache: "no-store"
    });
    const parsed = readinessSchema.safeParse(await response.json());
    if (parsed.success) {
      const { status, checks } = parsed.data;
      if (checks.startup === "not_ready") {
        return "后端服务正在启动，尚未准备好处理项目请求。请稍后重新加载。";
      }
      if (checks.metadata_database === "unavailable") {
        return "后端项目元数据库暂不可用。请稍后重试，若持续失败，请检查后端数据库连接。";
      }
      if (checks.mcp_transport === "not_ready") {
        return "后端查询服务尚未就绪。请稍后重新加载。";
      }
      if (response.ok && status === "ready") {
        return "后端当前已就绪，请重新加载项目。";
      }
    }
    return "暂时无法确认后端就绪状态。服务可能正在重启或响应缓慢，请稍后重新加载。";
  } catch {
    return "后端服务未响应，可能正在重启或热重载。请稍后重新加载，若持续失败，请检查后端服务。";
  }
}

/** Keep caller cancellation distinct from a request deadline or unavailable backend. */
export async function withProjectRequest<T>(
  baseUrl: string,
  operation: string,
  request: (signal: AbortSignal) => Promise<T>,
  signal?: AbortSignal
): Promise<T> {
  const deadline = AbortSignal.timeout(PROJECT_REQUEST_TIMEOUT_MS);
  const combined = signal ? AbortSignal.any([signal, deadline]) : deadline;
  try {
    combined.throwIfAborted();
    return await request(combined);
  } catch (error) {
    if (signal?.aborted && !isTimeout(signal.reason)) throw signal.reason;
    if (isTimeout(error) || (combined.aborted && isTimeout(combined.reason))) {
      const diagnosis = await describeServerReadiness(baseUrl);
      throw new Error(`${operation}超时（已等待 15 秒）。${diagnosis}`, { cause: error });
    }
    if (error instanceof TypeError || (error instanceof DOMException && error.name === "NetworkError")) {
      throw new Error(`${operation}失败：无法连接后端服务。请检查网络和后端服务状态后重试。`, { cause: error });
    }
    throw error;
  }
}