import { readFileSync } from "node:fs";
import { expect, it } from "vitest";

// One rule, two languages, no shared wire format — so a test is the only thing that holds them
// together. Which point a library item keeps is the server's (`routes/_common.kept_position`); the
// client repeats it (`lib/resume.ts`) for the shared link, which has no server side, and for the
// library row it patches before the server has answered. A server-only change left the row showing
// a Continue point the server had already cleared, and a link resuming at points the library no
// longer keeps. Both must be EQUAL: neither direction is merely conservative here.
//
// Read from source rather than imported, as in plexFinishMargin.contract.test.ts.
function constantIn(path: string, pattern: RegExp): number {
  const source = readFileSync(new URL(path, import.meta.url), "utf8");
  const m = pattern.exec(source);
  // If this fails the constant was renamed or moved — find it and re-point this test, because the
  // rule it guards did not go away.
  expect(m, `${pattern} not found in ${path}`).not.toBeNull();
  return Number(m![1]);
}

const SERVER = "../../../backend/app/routes/_common.py";

it.each([
  ["the least position that counts as started", "PROGRESS_MIN_SECONDS", "PROGRESS_MIN_S"],
  ["the margin before the end that counts as finished", "FINISH_MARGIN_SECONDS", "FINISH_MARGIN_S"],
])("keeps %s the same as the server", (_what, server, client) => {
  const backend = constantIn(SERVER, new RegExp(`^${server}\\s*=\\s*(\\d+)`, "m"));
  const frontend = constantIn("./resume.ts", new RegExp(`^const ${client}\\s*=\\s*(\\d+)`, "m"));
  expect(backend).toBeGreaterThan(0);
  expect(frontend).toBe(backend);
});