using UnityEngine;
using UnityEngine.UI;

namespace Utils
{
    public static class DragGhost
    {
        private static GameObject ghost;
        private static Image ghostImage;
        private static Canvas parentCanvas;
        private static CanvasGroup ghostCanvasGroup;

        // Ensure ghost exists under given canvas
        public static void Show(Canvas canvas, Sprite sprite)
        {
            if (canvas == null || sprite == null) return;
            if (ghost == null || parentCanvas != canvas)
            {
                if (ghost != null) Object.Destroy(ghost);
                parentCanvas = canvas;
                ghost = new GameObject("_SharedDragGhost");
                ghost.transform.SetParent(parentCanvas.transform, false);
                ghostImage = ghost.AddComponent<Image>();
                ghostImage.raycastTarget = false;
                ghostCanvasGroup = ghost.AddComponent<CanvasGroup>();
                ghostCanvasGroup.blocksRaycasts = false;
                ghostCanvasGroup.alpha = 0.5f; // Set transparency to half
            }
            ghostImage.sprite = sprite;
            // set size to sprite rect (avoid SetNativeSize to reduce layout work)
            var rt = ghostImage.rectTransform;
            rt.sizeDelta = new Vector2(sprite.rect.width, sprite.rect.height);
            ghost.SetActive(true);
        }

        public static void Hide()
        {
            if (ghost != null) ghost.SetActive(false);
        }

        public static void UpdatePosition(Vector2 screenPosition, Camera cam)
        {
            if (ghost == null || parentCanvas == null) return;
            RectTransformUtility.ScreenPointToLocalPointInRectangle(
                parentCanvas.transform as RectTransform,
                screenPosition,
                cam,
                out Vector2 localPoint);
            ghost.transform.localPosition = localPoint;
        }
    }
}