using System.Collections.Generic;
using Items;
using Terrain;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

namespace UI {
    public class DragAndDropHandler : MonoBehaviour {
        [SerializeField] private UIItemSlot cursorSlot = null;
        private ItemSlot _cursorItemSlot;
        [SerializeField] private GraphicRaycaster raycaster = null;
        private PointerEventData _pointerEventData;
        [SerializeField] private EventSystem eventSystem = null;

        private World _world;

        private void Start() {
            _world = GameObject.Find("World").GetComponent<World>();
            
            _cursorItemSlot = new ItemSlot(cursorSlot);
        }


        private void Update() {
            if (!_world.MenuOpen) return;

            cursorSlot.transform.position = Input.mousePosition + new Vector3(-24, 0, 0);

            if (Input.GetMouseButtonDown(0)) {
                HandleSlotClick(CheckForSlot());
            }
        }

        private void HandleSlotClick(UIItemSlot clickedSlot) {
            if (clickedSlot == null) return;
            if (!cursorSlot.HasItem && !clickedSlot.HasItem) return;

            if (clickedSlot.itemSlot.creative) {
                _cursorItemSlot.EmptySlot();
                _cursorItemSlot.InsertStack(clickedSlot.itemSlot.Stack);
                return;
            }

            if (!cursorSlot.HasItem && clickedSlot.HasItem) {
                _cursorItemSlot.InsertStack(clickedSlot.itemSlot.TakeAll());
                return;
            }
            
            if (cursorSlot.HasItem && !clickedSlot.HasItem) {
                clickedSlot.itemSlot.InsertStack(_cursorItemSlot.TakeAll());
                return;
            }

            if (cursorSlot.HasItem && clickedSlot.HasItem) {
                if (cursorSlot.itemSlot.Stack.Block != clickedSlot.itemSlot.Stack.Block) {
                    ItemStack oldCursorSlot = cursorSlot.itemSlot.TakeAll();
                    ItemStack oldSlot = clickedSlot.itemSlot.TakeAll();
                    
                    clickedSlot.itemSlot.InsertStack(oldCursorSlot);
                    cursorSlot.itemSlot.InsertStack(oldSlot);
                }
            }
        }

        private UIItemSlot CheckForSlot() {
            _pointerEventData = new PointerEventData(eventSystem);
            _pointerEventData.position = Input.mousePosition;

            List<RaycastResult> results = new List<RaycastResult>();
            raycaster.Raycast(_pointerEventData, results);
            
            foreach (RaycastResult result in results) {
                if (result.gameObject.CompareTag("UIItemSlot")) {
                    return result.gameObject.GetComponent<UIItemSlot>();
                }
            }
            
            return null;
        }
    }
}