//--------------------------------------------------------
//    [Author]:           玩个游戏
//    [  Date ]:           Monday, July 31, 2017
//--------------------------------------------------------
using UnityEngine;
using System.Collections;
using UnityEngine.EventSystems;
using System;
using UnityEngine.Events;

/// <summary>
/// 拖拽组件，实现拖拽功能并限制拖拽范围
/// </summary>
public class DragItem:MonoBehaviour,ICanvasRaycastFilter,IBeginDragHandler,IDragHandler,IEndDragHandler 
{
    [SerializeField] public Canvas parentCanvas;
    [SerializeField] public Canvas canvas;
    // 拖拽区域限制
    [SerializeField]
    RectTransform m_Area;
    public RectTransform area { get { return m_Area; } }

    // 是否允许射线检测
    [SerializeField]
    bool m_RaycastTarget = true;
    public bool raycastTarget {
        get { return m_RaycastTarget; }
        private set { m_RaycastTarget = value; }
    }

    [NonSerialized] public int pos;

    private DragContainer lastTransform;

    // 当前对象的RectTransform组件
    RectTransform rectTransform { get { return this.transform as RectTransform; } }


    /// <summary>
    /// 开始拖拽时调用
    /// </summary>
    public void OnBeginDrag(PointerEventData eventData)
    {
        raycastTarget = false;
        this.transform.position = UIUtility.ClampWorldPosition(area, eventData);
        rectTransform.localScale = Vector3.one * 1.2f;

        canvas.sortingLayerID =  parentCanvas.sortingLayerID;
        canvas.sortingOrder = parentCanvas.sortingOrder + pos + 10;
    }

    /// <summary>
    /// 拖拽过程中调用
    /// </summary>
    public void OnDrag(PointerEventData eventData) {
        this.transform.position = UIUtility.ClampWorldPosition(area,eventData);
        
        // 检测是否进入目标区域
        if (eventData.pointerEnter != null)
        {
            if (lastTransform != null && lastTransform != eventData.pointerEnter.GetComponent<DragContainer>())
            { 
                lastTransform.mainTransform.localScale = Vector3.one;
                lastTransform = null;
            }
            var target = eventData.pointerEnter.GetComponent<DragContainer>();
            // 输出组件路径
            if (target != null)
            {
                lastTransform = target;
                // 进入目标区域，放大 1.2 倍
                lastTransform.mainTransform.localScale = Vector3.one * 1.2f;
            }
        }
        rectTransform.localScale = Vector3.one * 1.2f;
    }

    /// <summary>
    /// 结束拖拽时调用
    /// </summary>
    public Action<int, int> onEndDragEvent;

    public void OnEndDrag(PointerEventData eventData)
    {
        raycastTarget = true;
        rectTransform.localScale = Vector3.one;
        
        if (lastTransform != null)
        {
            lastTransform.mainTransform.localScale = Vector3.one;
            lastTransform = null;
        }

        if (eventData.pointerEnter == null)
        {
            onEndDragEvent?.Invoke(pos, -1);
            return;
        }

        var container = eventData.pointerEnter.GetComponent<DragContainer>();
        if (container == null)
        {
            onEndDragEvent?.Invoke(pos, -1);
            return;
        }
        onEndDragEvent?.Invoke(pos, container.pos);
        canvas.sortingLayerID =  parentCanvas.sortingLayerID;
        canvas.sortingOrder = parentCanvas.sortingOrder + pos + 1;
    }

    /// <summary>
    /// 判断射线检测是否有效
    /// </summary>
    public bool IsRaycastLocationValid(Vector2 sp,Camera eventCamera) {
        return raycastTarget;
    }
}