diachron/express/context.ts

// context.ts
//
// Request-scoped context using AsyncLocalStorage.
// Allows services to access request data (like the current user) without
// needing to pass Call through every function.

import { AsyncLocalStorage } from "node:async_hooks";
import { AnonymousUser, type MaybeUser } from "./user";

type RequestContext = {
    user: MaybeUser;
};

const asyncLocalStorage = new AsyncLocalStorage<RequestContext>();

// Run a function within a request context
function runWithContext<T>(context: RequestContext, fn: () => T): T {
    return asyncLocalStorage.run(context, fn);
}

// Get the current user from context, or AnonymousUser if not in a request
function getCurrentUser(): MaybeUser {
    const context = asyncLocalStorage.getStore();
    return context?.user ?? AnonymousUser;
}

export { getCurrentUser, runWithContext, type RequestContext };