import { transferableAbortController } from 'node:util';
import { AiApiError, AiErrorCodes } from './AiError';

export interface AiTimeoutBudget {
  readonly signal: AbortSignal;
  remainingMs(): number;
  throwIfExpired(): void;
  dispose(): void;
}

export function createAiTimeoutBudget(
  timeoutMs: number,
  parentSignal?: AbortSignal,
): AiTimeoutBudget {
  const startedAt = performance.now();
  // Node fetch validates AbortSignal's realm.  Server code can temporarily run
  // beside a DOM realm during smoke rendering, so keep this timeout signal native.
  const controller = transferableAbortController();
  const timeout = setTimeout(() => {
    controller.abort(new DOMException('AI request timed out', 'TimeoutError'));
  }, timeoutMs);
  const onParentAbort = () => controller.abort(
    parentSignal?.reason ?? new DOMException('AI request aborted', 'AbortError'),
  );
  if (parentSignal?.aborted) {
    onParentAbort();
  } else {
    parentSignal?.addEventListener('abort', onParentAbort, { once: true });
  }

  const remainingMs = () => Math.max(0, Math.ceil(timeoutMs - (performance.now() - startedAt)));
  return {
    signal: controller.signal,
    remainingMs,
    throwIfExpired() {
      if (remainingMs() <= 0 || controller.signal.aborted) {
        throw new AiApiError(AiErrorCodes.AI_UPSTREAM_TIMEOUT, 'AI 服务调用超时');
      }
    },
    dispose() {
      clearTimeout(timeout);
      parentSignal?.removeEventListener('abort', onParentAbort);
    },
  };
}