geometry-tower-defense/Assets/GameMain/Scripts/UI/Game/View/RepoItem.cs

using GeometryTD.CustomEvent;
using GeometryTD.Definition;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

namespace GeometryTD.UI
{
    public class RepoItem : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
    {
        [SerializeField] private Image _bgImage;
        
        [SerializeField] private IconArea _iconArea;

        private static readonly Color SelectedColor = new Color32(255, 216, 102, 255);
        private static readonly Color EmptyEnduranceColor = new Color(0.8f, 0f, 0f, 1f);
        private static readonly Color FullEnduranceColor = new Color(0f, 0.8f, 0f, 1f);
        private static readonly Vector2 DefaultDragGhostSize = new Vector2(64f, 64f);

        [SerializeField] private RepoItemContext _context;
        private CanvasGroup _canvasGroup;
        private RectTransform _dragRoot;
        private GameObject _dragGhostObject;
        private RectTransform _dragGhostRect;
        private bool _isSelected;
        private bool _isDragging;
        private bool _dropHandled;
        private bool _dropAssigned;

        public RepoItemContext Context => _context;

        private void Awake()
        {
            _canvasGroup = GetComponent<CanvasGroup>();
            if (_canvasGroup == null)
            {
                _canvasGroup = gameObject.AddComponent<CanvasGroup>();
            }
        }

        private void OnDisable()
        {
            ResetDragState();
        }

        public void OnInit(RepoItemContext context)
        {
            if (context == null)
            {
                OnReset();
                return;
            }

            _context = context;

            _iconArea.OnInit(context.IconAreaContext);

            SetSelected(false);
            ResetDragState();
        }

        public void OnReset()
        {
            _context = null;
            _iconArea.OnReset();

            SetSelected(false);
            ResetDragState();
        }

        public void SetSelected(bool isSelected)
        {
            _isSelected = isSelected;
            RefreshBackgroundColor();
        }

        private void RefreshBackgroundColor()
        {
            if (_bgImage == null)
            {
                return;
            }

            if (_isSelected)
            {
                _bgImage.color = SelectedColor;
                return;
            }

            float enduranceRate = _context != null ? Mathf.Clamp01(_context.EnduranceRate01) : 1f;
            _bgImage.color = Color.Lerp(EmptyEnduranceColor, FullEnduranceColor, enduranceRate);
        }

        public void OnClick()
        {
            if (_context == null)
            {
                return;
            }

            if (_isDragging)
            {
                return;
            }

            GameEntry.Event.Fire(this, RepoItemClickedEventArgs.Create(_context.InstanceId, transform.position));
        }

        public void OnBeginDrag(PointerEventData eventData)
        {
            if (!CanStartDrag(eventData))
            {
                return;
            }

            _dragRoot = ResolveDragRoot();
            if (_dragRoot == null)
            {
                return;
            }

            _isDragging = true;
            _dropHandled = false;
            _dropAssigned = false;

            CloseItemDescFormIfOpen();

            if (!CreateDragGhost())
            {
                _isDragging = false;
                _dragRoot = null;
                return;
            }

            if (_canvasGroup != null)
            {
                _canvasGroup.blocksRaycasts = false;
            }

            SetSelected(true);
            UpdateDragGhostPosition(eventData);
        }

        public void OnDrag(PointerEventData eventData)
        {
            if (!_isDragging)
            {
                return;
            }

            UpdateDragGhostPosition(eventData);
        }

        public void OnEndDrag(PointerEventData eventData)
        {
            if (!_isDragging)
            {
                return;
            }

            bool assigned = _dropHandled && _dropAssigned;
            _isDragging = false;

            if (_canvasGroup != null)
            {
                _canvasGroup.blocksRaycasts = true;
            }
            DestroyDragGhost();
            _dragRoot = null;

            if (_context == null)
            {
                return;
            }

            GameEntry.Event.Fire(this, RepoItemDragEndedEventArgs.Create(_context.InstanceId, assigned));
        }

        public void SetDropResult(bool assigned)
        {
            if (!_isDragging)
            {
                return;
            }

            _dropHandled = true;
            _dropAssigned = assigned;
        }

        private bool CanStartDrag(PointerEventData eventData)
        {
            if (_context == null || _isDragging)
            {
                return false;
            }

            if (_isSelected && _context.ComponentSlotType != TowerCompSlotType.None)
            {
                return false;
            }

            if (!_context.CanDrag)
            {
                return false;
            }

            if (eventData == null || eventData.button != PointerEventData.InputButton.Left)
            {
                return false;
            }

            return true;
        }

        private static void CloseItemDescFormIfOpen()
        {
            var itemDescForm = GameEntry.UI.GetUIForm(UIFormType.ItemDescForm);
            if (itemDescForm != null)
            {
                GameEntry.UI.CloseUIForm(itemDescForm);
            }
        }

        private RectTransform ResolveDragRoot()
        {
            Canvas canvas = GetComponentInParent<Canvas>();
            if (canvas == null || canvas.rootCanvas == null)
            {
                return null;
            }

            return canvas.rootCanvas.transform as RectTransform;
        }

        private bool CreateDragGhost()
        {
            DestroyDragGhost();

            if (_dragRoot == null)
            {
                return false;
            }

            Sprite iconSprite = _iconArea != null ? _iconArea.CurrentIconSprite : null;
            Color iconColor = _iconArea != null ? _iconArea.CurrentIconColor : Color.white;
            Material iconMaterial = _iconArea != null ? _iconArea.CurrentIconMaterial : null;
            Vector2 iconSize = _iconArea != null ? _iconArea.CurrentIconSize : Vector2.zero;

            // Towers may not have an icon sprite; fall back to background sprite so drag still works.
            if (iconSprite == null && _bgImage != null)
            {
                iconSprite = _bgImage.sprite;
                iconColor = _bgImage.color;
                iconMaterial = _bgImage.material;
                iconSize = _bgImage.rectTransform.rect.size;
            }

            if (iconSprite == null)
            {
                return false;
            }

            _dragGhostObject = new GameObject("RepoItemDragGhost", typeof(RectTransform), typeof(CanvasGroup), typeof(Image));
            _dragGhostObject.layer = gameObject.layer;

            _dragGhostRect = _dragGhostObject.GetComponent<RectTransform>();
            _dragGhostRect.SetParent(_dragRoot, false);
            _dragGhostRect.anchorMin = new Vector2(0.5f, 0.5f);
            _dragGhostRect.anchorMax = new Vector2(0.5f, 0.5f);
            _dragGhostRect.pivot = new Vector2(0.5f, 0.5f);

            if (iconSize.x <= 0f || iconSize.y <= 0f)
            {
                iconSize = DefaultDragGhostSize;
            }
            _dragGhostRect.sizeDelta = iconSize;

            Image ghostImage = _dragGhostObject.GetComponent<Image>();
            ghostImage.raycastTarget = false;
            ghostImage.sprite = iconSprite;
            ghostImage.color = iconColor;
            ghostImage.material = iconMaterial;
            ghostImage.preserveAspect = true;

            CanvasGroup ghostCanvasGroup = _dragGhostObject.GetComponent<CanvasGroup>();
            ghostCanvasGroup.blocksRaycasts = false;
            ghostCanvasGroup.interactable = false;

            _dragGhostObject.transform.SetAsLastSibling();
            return true;
        }

        private void UpdateDragGhostPosition(PointerEventData eventData)
        {
            if (_dragGhostRect == null || _dragRoot == null || eventData == null)
            {
                return;
            }

            if (RectTransformUtility.ScreenPointToLocalPointInRectangle(_dragRoot, eventData.position,
                    eventData.pressEventCamera, out Vector2 localPoint))
            {
                _dragGhostRect.anchoredPosition = localPoint;
            }
        }

        private void DestroyDragGhost()
        {
            if (_dragGhostObject != null)
            {
                Destroy(_dragGhostObject);
                _dragGhostObject = null;
                _dragGhostRect = null;
            }
        }

        private void ResetDragState()
        {
            _isDragging = false;
            _dropHandled = false;
            _dropAssigned = false;
            _dragRoot = null;
            DestroyDragGhost();

            if (_canvasGroup != null)
            {
                _canvasGroup.blocksRaycasts = true;
            }
        }
    }
}