using UnityEngine;
using UnityEngine.UI;
using UnityEngine.Events;
using System.Collections.Generic;
using UnityEngine.EventSystems;
/// <summary>
/// 用于在Ui中切割Renderer的组件，类似RectMask2d；
/// 暂时未处理Mask嵌套的情况
/// </summary>
[DisallowMultipleComponent]
[RequireComponent(typeof(RectTransform))]
public class UICameraMask : UIBehaviour, IClipper
{
    private RectTransform rectTransform;
    private bool m_ShouldRecalculateClipRects;
    private List<UICameraMaskable> maskableList;
    private Vector4 clipArea;

    protected override void Awake()
    {
        base.Awake();
        rectTransform = (RectTransform)transform;
        maskableList = new List<UICameraMaskable>();
    }
    protected override void OnEnable()
    {
        base.OnEnable();
        m_ShouldRecalculateClipRects = true;
        ClipperRegistry.Register(this);
    }
    protected override void OnDisable()
    {
        base.OnDisable();
        maskableList.Clear();
        ClipperRegistry.Unregister(this);
    }
    // 暂时使用低端的transform.hasChanged Api来追踪Transform状态变化。
    // 用ClipperRegistry获得Clipping流程时间点。
    public virtual void PerformClipping()
    {
        if (IsTransformDirty(rectTransform))
            m_ShouldRecalculateClipRects = true;
        if (m_ShouldRecalculateClipRects)
        {
            m_ShouldRecalculateClipRects = false;
            ResetClipArea();
        }
    }

    public void AddClippable(UICameraMaskable clippable)
    {
        if (clippable == null)
            return;
        if (!maskableList.Contains(clippable))
            maskableList.Add(clippable);
        SetClipForOne(clippable);
    }

    public void RemoveClippable(UICameraMaskable clippable)
    {
        if (clippable == null)
            return;
        var index = maskableList.IndexOf(clippable);
        if (index >= 0)
        {
            maskableList.RemoveAt(index);
            RemoveClipForOne(clippable);
        }
    }

    private void ResetClipArea()
    {
        var corners = new Vector3[4];
        rectTransform.GetWorldCorners(corners);
        for (int i = 0; i < corners.Length; i++)
        {
            corners[i] = RectTransformUtility.WorldToScreenPoint(GetWorldCamera(), corners[i]);
            corners[i].x = corners[i].x / Screen.width * 2f - 1f;
            corners[i].y = corners[i].y / Screen.height * 2f - 1f;
        }
        clipArea = new Vector4(corners[0].x, corners[0].y, corners[2].x, corners[2].y);
        for (int i = 0; i < maskableList.Count; i++)
            SetClipForOne(maskableList[i]);
    }

    private void SetClipForOne(UICameraMaskable clippable)
    {
        clippable.SetClipRect(clipArea);
    }

    private Camera GetWorldCamera()
    {
        var uiManager = UIManager.Instance();
        if (uiManager)
            return uiManager.UICamera;
        else
            return Camera.main;
    }

    // 暂时使用transform.hasChanged api来检测Mask是否有变化
    Rect lastRect;
    private bool IsTransformDirty(RectTransform rectTransform)
    {
        bool result = false;
        if (rectTransform.hasChanged)
        {
            rectTransform.hasChanged = false;
            result = true;
        }
        else if (rectTransform.rect != lastRect)
            result = true;
        if (result)
            lastRect = rectTransform.rect;
        return result;
    }

    public static void RemoveClipForOne(UICameraMaskable clippable)
    {
        clippable.SetClipRect(new Vector4(-1f, -1f, 1f, 1f));
    }
}