PIM_6/Assets/_Scripts/DraggableObject.cs

using UnityEngine;

[RequireComponent(typeof(Collider))]
public class DraggableObject : MonoBehaviour
{
    [Header("Item")]
    public ItemType itemType;
    public Material normalMaterial;
    public Material highlightMaterial;
    public Material dragMaterial;
    public Material inactiveMaterial;
    public Vector3 startPosition;
    public bool isLocked;

    [Header("Drag")]
    public float dragLift = 0.35f;
    public float snapDistance = 1.25f;
    public bool isInteractable = true;

    private Camera mainCamera;
    private Renderer itemRenderer;
    private Plane dragPlane;
    private Vector3 dragOffset;
    private Vector3 returnPosition;
    private Slot highlightedSlot;
    private bool isDragging;
    private bool isMouseOver;

    private void Awake()
    {
        mainCamera = Camera.main;
        itemRenderer = GetComponent<Renderer>();
        startPosition = transform.position;
        returnPosition = startPosition;

        if (itemRenderer != null && normalMaterial == null)
        {
            normalMaterial = itemRenderer.sharedMaterial;
        }
    }

    private void Start()
    {
        ApplyNormalMaterial();
    }

    private void OnMouseEnter()
    {
        if (!CanInteract())
        {
            return;
        }

        isMouseOver = true;
        ApplyMaterial(highlightMaterial);
    }

    private void OnMouseExit()
    {
        isMouseOver = false;

        if (!isDragging && !isLocked)
        {
            ApplyNormalMaterial();
        }
    }

    private void OnMouseDown()
    {
        if (!CanInteract())
        {
            return;
        }

        if (mainCamera == null)
        {
            mainCamera = Camera.main;
        }

        // Запоминаем позицию перед перетаскиванием, чтобы вернуть предмет при ошибке.
        returnPosition = transform.position;
        dragPlane = new Plane(Vector3.up, new Vector3(0f, startPosition.y, 0f));

        if (TryGetMousePointOnDragPlane(out Vector3 mouseWorldPoint))
        {
            dragOffset = transform.position - mouseWorldPoint;
            dragOffset.y = 0f;
        }
        else
        {
            dragOffset = Vector3.zero;
        }

        isDragging = true;
        ApplyMaterial(dragMaterial != null ? dragMaterial : highlightMaterial);
    }

    private void OnMouseDrag()
    {
        if (!isDragging || !CanInteract())
        {
            return;
        }

        if (!TryGetMousePointOnDragPlane(out Vector3 mouseWorldPoint))
        {
            return;
        }

        // Offset сохраняет относительное положение курсора и предмета без резких скачков.
        Vector3 targetPosition = mouseWorldPoint + dragOffset;
        targetPosition.y = startPosition.y + dragLift;
        transform.position = targetPosition;

        UpdateSlotPreview();
    }

    private void OnMouseUp()
    {
        if (!isDragging)
        {
            return;
        }

        isDragging = false;
        // Предмет фиксируется только в ближайшем подходящем слоте.
        Slot nearestSlot = FindNearestSlot();
        ClearHighlightedSlot();

        if (nearestSlot != null && nearestSlot.CanAccept(this))
        {
            nearestSlot.PlaceItem(this);
            return;
        }

        transform.position = returnPosition;
        ApplyNormalMaterial();
    }

    public void LockToSlot(Vector3 slotPosition)
    {
        isLocked = true;
        isInteractable = false;
        transform.position = slotPosition;
        ApplyNormalMaterial();
    }

    public void SetInteractable(bool value)
    {
        if (isLocked)
        {
            isInteractable = false;
            return;
        }

        isInteractable = value;
        ApplyNormalMaterial();
    }

    public void SetNormalMaterial(Material material)
    {
        normalMaterial = material;
        ApplyNormalMaterial();
    }

    private bool CanInteract()
    {
        return isInteractable && !isLocked;
    }

    private bool TryGetMousePointOnDragPlane(out Vector3 worldPoint)
    {
        worldPoint = Vector3.zero;

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

        // Raycast в математическую плоскость делает drag стабильным для ортографической камеры.
        Ray ray = mainCamera.ScreenPointToRay(Input.mousePosition);
        if (!dragPlane.Raycast(ray, out float distance))
        {
            return false;
        }

        worldPoint = ray.GetPoint(distance);
        return true;
    }

    private void UpdateSlotPreview()
    {
        Slot nearestSlot = FindNearestSlot();

        if (nearestSlot == highlightedSlot)
        {
            return;
        }

        ClearHighlightedSlot();
        highlightedSlot = nearestSlot;

        if (highlightedSlot != null)
        {
            highlightedSlot.ShowPreview(this);
        }
    }

    private Slot FindNearestSlot()
    {
        Slot[] slots = FindObjectsOfType<Slot>();
        Slot nearest = null;
        float bestDistance = snapDistance;

        foreach (Slot slot in slots)
        {
            float distance = Vector3.Distance(transform.position, slot.transform.position);
            if (distance <= bestDistance)
            {
                bestDistance = distance;
                nearest = slot;
            }
        }

        return nearest;
    }

    private void ClearHighlightedSlot()
    {
        if (highlightedSlot != null)
        {
            highlightedSlot.ClearPreview();
            highlightedSlot = null;
        }
    }

    private void ApplyNormalMaterial()
    {
        if (isLocked)
        {
            ApplyMaterial(normalMaterial);
            return;
        }

        if (isMouseOver && CanInteract())
        {
            ApplyMaterial(highlightMaterial);
            return;
        }

        if (!isInteractable && inactiveMaterial != null)
        {
            ApplyMaterial(inactiveMaterial);
            return;
        }

        ApplyMaterial(normalMaterial);
    }

    private void ApplyMaterial(Material material)
    {
        if (itemRenderer != null && material != null)
        {
            itemRenderer.sharedMaterial = material;
        }
    }
}