let order: string[] = [];
const listeners = new Set<() => void>();
let host: HTMLDivElement | undefined;
export type FloatingWindowEntry = { id: string; title: string; focus: () => void; close: () => void };
const registered = new Map<string, {
  entry: FloatingWindowEntry;
  actions: Pick<FloatingWindowEntry, "focus" | "close">;
}>();
let entries: readonly FloatingWindowEntry[] = [];

function publishWindows() {
  entries = order.flatMap((id) => {
    const record = registered.get(id);
    return record ? [record.entry] : [];
  });
  listeners.forEach((listener) => listener());
}

export const floatingWindowOrder = () => order;
/** Stable between changes, ordered from the back window to the foreground. */
export const floatingWindowEntries = () => entries;
export const subscribeFloatingWindows = (listener: () => void) => {
  listeners.add(listener);
  return () => { listeners.delete(listener); };
};

export function registerFloatingWindow(entry: FloatingWindowEntry) {
  const previous = registered.get(entry.id);
  if (previous) {
    // Callbacks can change without invalidating the subscribed presentation.
    previous.actions.focus = entry.focus;
    previous.actions.close = entry.close;
    if (previous.entry.title === entry.title) return;
    previous.entry = { ...previous.entry, title: entry.title };
  } else {
    const actions = { focus: entry.focus, close: entry.close };
    registered.set(entry.id, { actions, entry: { id: entry.id, title: entry.title,
      focus: () => { if (registered.get(entry.id)?.actions === actions) actions.focus(); },
      close: () => { if (registered.get(entry.id)?.actions === actions) actions.close(); } } });
    if (!order.includes(entry.id)) order = [...order, entry.id];
  }
  publishWindows();
}

export function raiseFloatingWindow(id: string) {
  if (order.at(-1) === id) return;
  order = [...order.filter((item) => item !== id), id];
  publishWindows();
}

export function removeFloatingWindow(id: string) {
  if (!order.includes(id) && !registered.has(id)) return;
  registered.delete(id);
  order = order.filter((item) => item !== id);
  publishWindows();
}

export function floatingWindowHost() {
  if (!host?.isConnected) {
    host = document.createElement("div");
    // One stacking context keeps windows below dialogs and newly opened menus.
    host.className = "pointer-events-none fixed inset-0 z-50";
    host.dataset.floatingWindowLayer = "";
    document.body.appendChild(host);
  }
  return host;
}