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import type { ExportRequest, ExportResult, WorkerInbound, WorkerOutbound } from "../types";
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/**
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 * Main-thread handle to the export worker. The worker owns the heavy pixel work
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 * (decode → transform → encode); here we just correlate requests/responses by id
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 * and hand back a promise. The source bytes are transferred (not copied).
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 */
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let worker: Worker | null = null;
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let seq = 0;
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const pending = new Map<number, { resolve: (r: ExportResult) => void; reject: (e: Error) => void }>();
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function getWorker(): Worker {
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  if (worker) return worker;
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  worker = new Worker(new URL("../workers/export.worker.ts", import.meta.url), {
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    type: "module",
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    name: "wimp-export",
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  });
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  worker.onmessage = (e: MessageEvent<WorkerOutbound>) => {
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    const { id, response } = e.data;
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    const entry = pending.get(id);
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    if (!entry) return;
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    pending.delete(id);
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    if (response.ok) entry.resolve(response);
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    else entry.reject(new Error(response.error));
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  };
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  worker.onerror = (e: ErrorEvent) => {
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    const message = e.message || "The export worker crashed.";
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    for (const [, entry] of pending) entry.reject(new Error(message));
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    pending.clear();
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    // Drop the broken worker; the next request spins up a fresh one.
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    worker?.terminate();
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    worker = null;
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  };
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  return worker;
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}
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export function exportImage(req: ExportRequest): Promise<ExportResult> {
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  const w = getWorker();
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  const id = ++seq;
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  const message: WorkerInbound = { id, request: req };
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  return new Promise<ExportResult>((resolve, reject) => {
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    pending.set(id, { resolve, reject });
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    w.postMessage(message, { transfer: [req.bytes] });
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  });
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}