sandboxRunner.ts

import type { SandboxWorkerRequest, SandboxWorkerResponse } from "@/types/sandbox";

let worker: Worker | null = null;
let nextId = 1;

function getWorker(): Worker {
  if (!worker) {
    worker = new Worker(new URL("../workers/sandbox.worker.ts", import.meta.url), {
      type: "module",
    });
  }
  return worker;
}

/**
 * Evaluates a numeric expression off the main thread (module worker).
 * The worker only runs {@link evaluateSafeNumericExpression}; no general JS execution.
 */
export function evaluateInSandbox(expr: string): Promise<number> {
  const id = nextId++;
  const w = getWorker();
  return new Promise((resolve, reject) => {
    const handler = (ev: MessageEvent<SandboxWorkerResponse>) => {
      if (ev.data.id !== id) return;
      w.removeEventListener("message", handler);
      if (ev.data.ok) resolve(ev.data.value);
      else reject(new Error(ev.data.error));
    };
    w.addEventListener("message", handler);
    const req: SandboxWorkerRequest = { id, type: "eval", expr };
    w.postMessage(req);
  });
}