/** Modifier-held preview lifecycle; surfaces own their target and semantic commit. */
export function installKeyboardStaging<T>(options: {
  host: HTMLElement;
  owns: (element: HTMLElement) => boolean;
  onCancel: () => void;
  onCommit: (value: T) => void;
}) {
  let staged: { source: HTMLElement; value: T; releaseKey: string } | null = null;
  const cancel = () => {
    if (!staged) return;
    staged = null;
    options.host.removeAttribute("data-key-staging");
    options.onCancel();
  };
  const commit = () => {
    if (!staged) return;
    const value = staged.value;
    staged = null;
    options.host.removeAttribute("data-key-staging");
    options.onCommit(value);
  };
  const onKeyUp = (event: KeyboardEvent) => {
    if (staged?.releaseKey === event.key) commit();
  };
  const onPointerDown = (event: PointerEvent) => {
    if (event.target instanceof HTMLElement && options.owns(event.target)) cancel();
  };
  const onFocus = (event: FocusEvent) => {
    if (staged && event.target !== staged.source) cancel();
  };
  window.addEventListener("keyup", onKeyUp);
  window.addEventListener("blur", commit);
  options.host.addEventListener("pointerdown", onPointerDown);
  document.addEventListener("focusin", onFocus, true);
  return {
    get current(): T | null {
      return staged?.value ?? null;
    },
    set(source: HTMLElement, value: T, event: KeyboardEvent, releaseKey?: string) {
      staged = {
        source,
        value,
        releaseKey:
          releaseKey ??
          (event.altKey
            ? "Alt"
            : event.shiftKey
              ? "Shift"
              : event.ctrlKey
                ? "Control"
                : event.metaKey
                  ? "Meta"
                  : event.key),
      };
      options.host.setAttribute("data-key-staging", "");
    },
    cancel,
    dispose() {
      cancel();
      window.removeEventListener("keyup", onKeyUp);
      window.removeEventListener("blur", commit);
      options.host.removeEventListener("pointerdown", onPointerDown);
      document.removeEventListener("focusin", onFocus, true);
    },
  };
}