using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;

public class PerspectiveScrollRect : MonoBehaviour
{
    /// <summary>
    /// 中心點(diǎn)，中心點(diǎn)可以設(shè)置為不是原點(diǎn)
    /// </summary>
    public Vector3 uiCenterPoint = Vector3.zero;

    /// <summary>
    /// 圖片的回拉像素，每距離中心點(diǎn)100個(gè)像素往回拉的距離
    /// </summary>
    [Range(0,100)]
    public float perspective = 0;

    public ScrollRect scrollRect;

    /// <summary>
    /// 滑動(dòng)列表節(jié)點(diǎn)
    /// </summary>
    private RectTransform scrollRectRectTransform;
    private List<RectTransform> childRectTransformList = new List<RectTransform>();
    private RectTransform rectTransform;

    private void Start()
    {
        scrollRectRectTransform = scrollRect.GetComponent<RectTransform>();
        rectTransform = GetComponent<RectTransform>();
        for(int i = 0;i < transform.childCount;i++)
        {
            if(transform.GetChild(i).gameObject.activeInHierarchy)
            {
                childRectTransformList.Add(transform.GetChild(i).GetComponent<RectTransform>());
            }
        }
        scrollRect.onValueChanged.AddListener(UpdataChilds);
        UpdataChilds(Vector2.zero);
    }

    void UpdataChilds(Vector2 vector2)
    {
        ModifyMesh(new VertexHelper());
    }

    public void ModifyMesh(VertexHelper vh)
    {
        if (!gameObject.activeInHierarchy || childRectTransformList.Count <= 0)
        {
            return;
        }

        foreach(var item in childRectTransformList)
        {
            float offset_left;
            float offset_right;
            Vector3 distanceVector = new Vector3(item.localPosition.x - scrollRectRectTransform.sizeDelta.x / 2 + rectTransform.anchoredPosition.x, item.localPosition.y, 0) - uiCenterPoint;
            //distanceVector.x小于0則證明當(dāng)前節(jié)點(diǎn)在中心點(diǎn)右邊，設(shè)置的透視左右值需要反過(guò)來(lái)
            if (distanceVector.x < 0)
            {
                offset_left = -perspective * distanceVector.x / 100f;
                offset_right = -perspective * distanceVector.x / 100f;
            }
            else
            {
                offset_left = -perspective * distanceVector.x / 100f;
                offset_right = -perspective * distanceVector.x / 100f;
            }
            Image[] images = item.GetComponentsInChildren<Image>();
            Text[] texts = item.GetComponentsInChildren<Text>();
            ModifyImagesInItem(offset_left, offset_right, images, item.sizeDelta.y);
            ModifyTextsInItem(offset_left, offset_right, texts, item.sizeDelta.y);
        }

    }

    public void ModifyImagesInItem(float offset_left, float offset_right, Image[] images, float itemHeight)
    {
        VertexHelper vh = new VertexHelper();
        for (int i = 0; i < images.Length; i++)
        {
            Graphic graphic = images[i];
            vh.Clear();
            graphic.OnPopulateMesh_Public(vh);

            var vertexs = new List<UIVertex>();
            vh.GetUIVertexStream(vertexs);

            UIVertex vt;
            float ratio0;
            float ratio1;
            float ratio2;
            float ratio3;
            float graphicPosY = Mathf.Abs(graphic.rectTransform.localPosition.y);

            vt = vertexs[0];
            ratio0 = (Mathf.Abs(vt.position.y) + graphicPosY) / itemHeight;
            vt.position += new Vector3(offset_left * ratio0, 0, 0);
            vh.SetUIVertex(vt, 0);

            vt = vertexs[1];
            ratio1 = (Mathf.Abs(vt.position.y) + graphicPosY) / itemHeight;
            vt.position += new Vector3(offset_left * ratio1, 0, 0);
            vh.SetUIVertex(vt, 1);

            vt = vertexs[2];
            ratio2 = (Mathf.Abs(vt.position.y) + graphicPosY) / itemHeight;
            vt.position += new Vector3(offset_right * ratio2, 0, 0);
            vh.SetUIVertex(vt, 2);

            vt = vertexs[4];
            ratio3 = (Mathf.Abs(vt.position.y) + graphicPosY) / itemHeight;
            vt.position += new Vector3(offset_right * ratio3, 0, 0);
            vh.SetUIVertex(vt, 3);

            Mesh mesh = new Mesh();
            vh.FillMesh(mesh);
            graphic.canvasRenderer.SetMesh(mesh);
            MeshCollider meshCollider = graphic.GetComponent<MeshCollider>();
            if(meshCollider != null)
            {
                meshCollider.sharedMesh = mesh;
            }
        }
    }

    public void ModifyTextsInItem(float offset_left, float offset_right, Text[] texts, float itemHeight)
    {
        VertexHelper vh = new VertexHelper();
        for (int i = 0; i < texts.Length; i++)
        {
            Graphic graphic = texts[i];
            vh.Clear();
            graphic.OnPopulateMesh_Public(vh);

            var vertexs = new List<UIVertex>();
            vh.GetUIVertexStream(vertexs);

            UIVertex vt;
            float ratio;
            float graphicPosY = Mathf.Abs(graphic.rectTransform.localPosition.y);

            int vert_index = 0;

            for (int j = 0; j < vertexs.Count; j++)
            {
                //剔除不必要的頂點(diǎn)
                if((j - 3) % 6 == 0 || (j - 5) % 6 == 0)
                {
                    continue;
                }

                if((j - 0) % 6 == 0 || (j - 1) % 6 == 0)
                {
                    vt = vertexs[j];
                    ratio = (Mathf.Abs(vt.position.y) + graphicPosY) / itemHeight;
                    vt.position += new Vector3(offset_left * ratio, 0, 0);
                    vh.SetUIVertex(vt, vert_index);
                    vert_index++;
                }

                if((j - 2) % 6 == 0 || (j - 4) % 6 == 0)
                {
                    vt = vertexs[j];
                    ratio = (Mathf.Abs(vt.position.y) + graphicPosY) / itemHeight;
                    vt.position += new Vector3(offset_right * ratio, 0, 0);
                    vh.SetUIVertex(vt, vert_index);
                    vert_index++;
                }
            }

            Mesh mesh = new Mesh();
            vh.FillMesh(mesh);
            graphic.canvasRenderer.SetMesh(mesh);
            MeshCollider meshCollider = graphic.GetComponent<MeshCollider>();
            if (meshCollider != null)
            {
                meshCollider.sharedMesh = mesh;
            }
        }
    }
}

public void OnPopulateMesh_Public(VertexHelper toFill)
{
    OnPopulateMesh(toFill);
}

protected virtual void OnPopulateMesh(VertexHelper vh)
{
    var r = GetPixelAdjustedRect();
    var v = new Vector4(r.x, r.y, r.x + r.width, r.y + r.height);

    Color32 color32 = color;
    vh.Clear();
    vh.AddVert(new Vector3(v.x, v.y), color32, new Vector2(0f, 0f));
    vh.AddVert(new Vector3(v.x, v.w), color32, new Vector2(0f, 1f));
    vh.AddVert(new Vector3(v.z, v.w), color32, new Vector2(1f, 1f));
    vh.AddVert(new Vector3(v.z, v.y), color32, new Vector2(1f, 0f));

    vh.AddTriangle(0, 1, 2);
    vh.AddTriangle(2, 3, 0);
}