/**
 * 手机/平板双指与手势缩放锁（头像裁剪、图片灯箱区域放行 pinch）。
 *
 * 只监听用户手势事件，而手势必然发生在页面加载与客户端 bundle 执行之后，
 * 因此无需像主题脚本那样内联在 <head> 中，在客户端入口安装即可。
 */
export function installZoomGuard(): void {
  if (typeof document === 'undefined') return;

  const inZoomAllowArea = (target: EventTarget | null): boolean =>
    !!target
      && target instanceof Element
      && typeof target.closest === 'function'
      && !!target.closest('.avatar-crop-stage, .image-lightbox');

  const blockGesture = (e: Event) => {
    if (inZoomAllowArea(e.target)) return;
    if (e.cancelable) e.preventDefault();
  };

  const blockMultiTouch = (e: TouchEvent) => {
    if (e.touches && e.touches.length > 1) {
      if (inZoomAllowArea(e.target)) return;
      if (e.cancelable) e.preventDefault();
    }
  };

  document.addEventListener('gesturestart', blockGesture, { passive: false });
  document.addEventListener('gesturechange', blockGesture, { passive: false });
  document.addEventListener('gestureend', blockGesture, { passive: false });
  document.addEventListener('touchstart', blockMultiTouch, { passive: false });
  document.addEventListener('touchmove', blockMultiTouch, { passive: false });
}