import { AsyncLocalStorage } from "node:async_hooks";
import { generateId } from "../utils";

// Request-scoped propagation. Populated by the HTTP middleware and by the
// event-dispatcher when it runs an MSP-apply, so ctx.appendEvent downstream
// automatically stamps the right provenance on every event it writes.
//
//   requestId     — unique per HTTP request (or Job run). Log correlation.
//   correlationId — the end-to-end business operation id; propagates across
//                   service boundaries and MSP causation chains. Comes from
//                   the `x-correlation-id` header if set, otherwise mirrors
//                   requestId (clients that don't set the header pay no
//                   penalty — a single HTTP call == one correlation).
//   causationId   — the events.id that triggered THIS execution. Null for
//                   root HTTP commands; set when an MSP-apply is running
//                   (event-dispatcher wraps the handler call). Together
//                   with correlationId, forms a causal DAG across streams.
//   signal        — AbortSignal from the underlying HTTP request. Aborts
//                   when the client disconnects (mobile back-press, tab
//                   close). Long-running framework code (event streaming,
//                   projection rebuild) checks signal.aborted at chunk
//                   boundaries; short queries don't pay the overhead.
//                   Undefined for non-HTTP entry-points (jobs, MSP-applies).
export type RequestContextData = {
  readonly requestId: string;
  readonly correlationId: string;
  readonly causationId?: string;
  readonly signal?: AbortSignal;
  // Client IP for per-IP rate limiting (L1, L2, L3 with per: "ip*").
  // Populated by requestIdMiddleware from x-forwarded-for or the
  // socket address. Undefined for non-HTTP entry points (jobs, MSP).
  readonly ip?: string;
  // Raw User-Agent header — audit trails (download tokens, GDPR export
  // access) want it alongside `ip`. Undefined for non-HTTP entry points.
  readonly userAgent?: string;
  // Client-declared active UI locale (BCP-47), resolved once from
  // X-Locale / Accept-Language by requestIdMiddleware — see
  // request-locale.ts. Undefined when neither header carried a valid tag;
  // callers fall back further (dispatch-shared.ts's ctx.locale chain).
  readonly locale?: string;
};

const storage = new AsyncLocalStorage<RequestContextData>();

export const requestContext = {
  run<T>(data: RequestContextData, fn: () => T): T {
    return storage.run(data, fn);
  },

  get(): RequestContextData | undefined {
    return storage.getStore();
  },

  generateId(): string {
    return generateId();
  },
};