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

public class UIGradient : BaseMeshEffect
{
    [SerializeField]
    private DirType _dir = DirType.Vertical;
    [SerializeField]
    private BlendType _blend = BlendType.Override;
    [SerializeField, Range(-1, 1)]
    private float _offset = 0f;
    [SerializeField]
    private Gradient _gradient = new Gradient() { colorKeys = new GradientColorKey[] { new GradientColorKey(Color.black, 0), new GradientColorKey(Color.white, 1) } };

    public override void ModifyMesh(VertexHelper vh)
    {
        if (!IsActive() || vh.currentVertCount == 0)
        {
            return;
        }

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

        bool isX = true;
        switch (_dir)
        {
            case DirType.Horizontal:
                isX = true;
                break;
            case DirType.Vertical:
                isX = false;
                break;
            default:
                break;
        }

        var inverseLength = GetInverseLength(vertexs, isX, out float min, out float max);

        var vertex = new UIVertex();
        for (int i = 0; i < vh.currentVertCount; i++)
        {
            vh.PopulateUIVertex(ref vertex, i);
            vertex.color = BlendColor(vertex.color, _gradient.Evaluate((isX ? (vertex.position.x - min) : (vertex.position.y - min)) * inverseLength - _offset), _blend);
            vh.SetUIVertex(vertex, i);
        }

    }

    // 若isX是false，则认为是y
    private float GetInverseLength(List<UIVertex> vertexs, bool isX, out float min, out float max)
    {
        float inverseLength = 0;
        min = isX ? vertexs[0].position.x : vertexs[0].position.y;
        max = min;
        for (int i = 1; i < vertexs.Count; i++)
        {
            var temp = isX ? vertexs[i].position.x : vertexs[i].position.y;

            if (temp > max)
            {
                max = temp;
            }
            else if (temp < min)
            {
                min = temp;
            }
        }

        inverseLength = 1 / (max - min);
        return inverseLength;
    }

    private Color BlendColor(Color originalColor, Color newColor, BlendType blendType)
    {
        var ret = newColor;
        switch (blendType)
        {
            case BlendType.Override: ret = newColor; break;
            case BlendType.Add: ret = originalColor + newColor; break;
            case BlendType.Multiply: ret = originalColor * newColor; break;
            default: break;
        }

        return ret;
    }

    private enum DirType
    {
        None,
        Horizontal,
        Vertical,
    }

    private enum BlendType
    {
        None,
        Override,
        Add,
        Multiply
    }
}