type ProgressEvent = "start" | "done";
type Listener = (event: ProgressEvent) => void;

const listeners = new Set<Listener>();
let active = false;

function emit(event: ProgressEvent) {
  listeners.forEach((listener) => listener(event));
}

export function subscribeNavigationProgress(listener: Listener) {
  listeners.add(listener);

  return () => {
    listeners.delete(listener);
  };
}

export function startNavigationProgress() {
  if (active) {
    return;
  }

  active = true;
  emit("start");
}

export function completeNavigationProgress() {
  if (!active) {
    return;
  }

  active = false;
  emit("done");
}