// One Mandelbrot band, computed in its own wasm instance.
//
// Each worker instantiates its own copy of the module. That is the whole
// reason this needs no SharedArrayBuffer and no COOP/COEP headers: nothing is
// shared, so there is nothing to synchronise. The wasm is ~34 KB, so N copies
// is cheap.
importScripts('nimflutter.js');

const SIG = ['number', 'number', 'number', 'number', 'number',
             'number', 'number', 'number', 'number', 'number'];

let mod = null;
const ready = createNimFlutterModule().then((m) => {
  mod = m;
  m.ccall('nf_init', null, [], []);
});

self.onmessage = async (e) => {
  await ready;
  const { id, w, h, cx, cy, scale, iter, y0, y1 } = e.data;

  const bytes = (y1 - y0) * w * 4;
  const buf = mod._malloc(bytes);
  try {
    mod.ccall('nf_mandelbrot', null, SIG,
              [buf, bytes, w, h, cx, cy, scale, iter, y0, y1]);
    // .slice() copies out of the wasm heap, which may be detached by a later
    // growth; the copy is then transferred rather than structured-cloned.
    const band = mod.HEAPU8.slice(buf, buf + bytes);
    self.postMessage({ id, y0, band }, [band.buffer]);
  } finally {
    mod._free(buf);
  }
};