import { test } from "node:test";
import assert from "node:assert/strict";
import type { StreamActionResult } from "../jobs/streamCommand";
import type { StreamActionView } from "./streamAction";

// THE ASSIGNABILITY, ASSERTED AT COMPILE TIME.
//
// `StreamActionLog` takes a `() => Promise<StreamActionView>` while every
// caller hands it a server action returning `StreamActionResult`. That only
// keeps working while the richer dispatch-layer type stays assignable to the
// narrower view. If someone renames a field on either side, `tsc --noEmit`
// fails HERE, naming both types, instead of failing at the twenty-odd call
// sites with a wall of structural mismatch.
//
// tsc sees this file; the runtime assertion below only exists so the file is a
// test rather than a lint the suite would skip.
//
// BOTH SIDES ARE WRAPPED IN TUPLES, and that is the whole assertion. A bare
// `A extends B ? …` DISTRIBUTES over a naked union type parameter: it would
// check each member of `StreamActionResult` separately and union the results,
// so a member that does not fit contributes `never` — and `true | never` is
// `true`. The check would pass while being wrong about exactly the case it
// exists to catch. `[A] extends [B]` defeats the distribution and compares the
// unions whole.
type AssignableTo<A, B> = [A] extends [B] ? true : never;
const _resultIsAView: AssignableTo<StreamActionResult, StreamActionView> = true;

test("StreamActionResult is assignable to StreamActionView", () => {
  assert.equal(_resultIsAView, true);
});