// One queue for the records screen: visible previews get four network slots.
const waiting: Array<() => void> = [];
let active = 0;
function pump() {
  while (active < 4 && waiting.length) waiting.shift()?.();
}
export function queuePreview(start: (release: () => void) => void) {
  let released = false;
  let started = false;
  const release = () => {
    if (released) return;
    released = true;
    if (started) active--;
    else {
      const index = waiting.indexOf(run);
      if (index >= 0) waiting.splice(index, 1);
    }
    pump();
  };
  const run = () => {
    started = true;
    active++;
    start(release);
  };
  waiting.push(run);
  pump();
  // Active fetches release their slot in finally, after abort has settled.
  return () => {
    if (!started) release();
  };
}