import "server-only";
import { after } from "next/server";

const workerKey = "__generated_image_archive_worker__";
type Worker = {
  running: boolean;
  scheduled: boolean;
  requested: boolean;
  retryTimer?: ReturnType<typeof setTimeout>;
};
function getWorker(): Worker {
  const root = globalThis as typeof globalThis & { [workerKey]?: Worker };
  return (root[workerKey] ??= { running: false, scheduled: false, requested: false });
}

export function scheduleImageArchiveWorker(deliveryConfirmed = false) {
  const worker = getWorker();
  worker.requested = true;
  if (worker.running || (worker.scheduled && !deliveryConfirmed)) return;
  worker.scheduled = true;
  if (worker.retryTimer) {
    clearTimeout(worker.retryTimer);
    worker.retryTimer = undefined;
  }
  const run = async () => {
    if (worker.running) return;
    worker.scheduled = false;
    worker.running = true;
    let retryNeeded = false;
    try {
      const { runImageArchiveJob } = await import("@/lib/jobs/image-archive-job");
      do {
        worker.requested = false;
        const result = await runImageArchiveJob();
        retryNeeded = result.stats.pendingStore > 0 || result.stats.pendingReplace > 0;
        // Stop when only backoff tasks remain; do not spin while storage is down.
        if (!worker.requested && result.store.total === 0 && result.replace.total === 0) break;
      } while (true);
    } catch (error) {
      retryNeeded = true;
      console.error("[ImageArchiveWorker] background archive failed", error);
    } finally {
      worker.running = false;
      if (worker.requested) scheduleImageArchiveWorker();
      else if (retryNeeded) {
        worker.retryTimer = setTimeout(scheduleImageArchiveWorker, 60_000);
        worker.retryTimer.unref?.();
      }
    }
  };
  // Detached generation tasks may inherit a request that has already closed. Keep
  // a Node-server fallback so archiving never depends on the user leaving a tab open.
  const deliveryFallback = setTimeout(() => {
    if (worker.scheduled && !worker.running) void run();
  }, 1_000);
  deliveryFallback.unref?.();
  try {
    // Request handlers deliver first. Durable task rows also allow cron/restart recovery.
    after(run);
  } catch {
    // Durable canvas tasks can run outside Next's request context on the Node server.
    setImmediate(() => {
      void run();
    });
  }
}