/// Credit Brad Nelson (playemgames - bitbucket)
/// Modified Gradient effect script from http://answers.unity3d.com/questions/1086415/gradient-text-in-unity-522-basevertexeffect-is-obs.html
/// <summary>
/// -Uses Unity's Gradient class to define the color
/// -Offset is now limited to -1,1
/// -Multiple color blend modes
///
/// Remember that for radial and diamond gradients, colors are applied per-vertex so if you have multiple points on your gradient where the color changes and there aren't enough vertices, you won't see all of the colors.
/// </summary>

using System;
using System.Collections.Generic;

namespace UnityEngine.UI.Extensions
{
    [AddComponentMenu("UI/Effects/Extensions/Gradient2")]
    public class Gradient2 : BaseMeshEffect
    {
        public enum Blend
        {
            Override,
            Add,
            Multiply
        }

        public enum Type
        {
            Horizontal,
            Vertical,
            Radial,
            Diamond
        }

        [SerializeField] private Type _gradientType;

        [SerializeField] private Blend _blendMode = Blend.Multiply;

        [SerializeField]
        [Tooltip(
            "Add vertices to display complex gradients. Turn off if your shape is already very complex, like text.")]
        private bool _modifyVertices = true;

        [SerializeField] [Range(-1, 1)] private float _offset;

        [SerializeField] [Range(0.1f, 10)] private float _zoom = 1f;

        [SerializeField] private UnityEngine.Gradient _effectGradient = new()
            { colorKeys = new[] { new GradientColorKey(Color.black, 0), new GradientColorKey(Color.white, 1) } };

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

            var _vertexList = new List<UIVertex>();

            helper.GetUIVertexStream(_vertexList);

            var nCount = _vertexList.Count;
            switch (GradientType)
            {
                case Type.Horizontal:
                case Type.Vertical:
                {
                    var bounds = GetBounds(_vertexList);
                    var min = bounds.xMin;
                    var w = bounds.width;
                    Func<UIVertex, float> GetPosition = v => v.position.x;

                    if (GradientType == Type.Vertical)
                    {
                        min = bounds.yMin;
                        w = bounds.height;
                        GetPosition = v => v.position.y;
                    }

                    var width = w == 0f ? 0f : 1f / w / Zoom;
                    var zoomOffset = (1 - 1 / Zoom) * 0.5f;
                    var offset = Offset * (1 - zoomOffset) - zoomOffset;

                    if (ModifyVertices) SplitTrianglesAtGradientStops(_vertexList, bounds, zoomOffset, helper);

                    var vertex = new UIVertex();
                    for (var i = 0; i < helper.currentVertCount; i++)
                    {
                        helper.PopulateUIVertex(ref vertex, i);
                        vertex.color = BlendColor(vertex.color,
                            EffectGradient.Evaluate((GetPosition(vertex) - min) * width - offset));
                        helper.SetUIVertex(vertex, i);
                    }
                }
                    break;

                case Type.Diamond:
                {
                    var bounds = GetBounds(_vertexList);

                    var height = bounds.height == 0f ? 0f : 1f / bounds.height / Zoom;
                    var radius = bounds.center.y / 2f;
                    var center = (Vector3.right + Vector3.up) * radius + Vector3.forward * _vertexList[0].position.z;

                    if (ModifyVertices)
                    {
                        helper.Clear();
                        for (var i = 0; i < nCount; i++) helper.AddVert(_vertexList[i]);

                        var centralVertex = new UIVertex();
                        centralVertex.position = center;
                        centralVertex.normal = _vertexList[0].normal;
                        centralVertex.uv0 = new Vector2(0.5f, 0.5f);
                        centralVertex.color = Color.white;
                        helper.AddVert(centralVertex);

                        for (var i = 1; i < nCount; i++) helper.AddTriangle(i - 1, i, nCount);
                        helper.AddTriangle(0, nCount - 1, nCount);
                    }

                    var vertex = new UIVertex();

                    for (var i = 0; i < helper.currentVertCount; i++)
                    {
                        helper.PopulateUIVertex(ref vertex, i);

                        vertex.color = BlendColor(vertex.color, EffectGradient.Evaluate(
                            Vector3.Distance(vertex.position, center) * height - Offset));

                        helper.SetUIVertex(vertex, i);
                    }
                }
                    break;

                case Type.Radial:
                {
                    var bounds = GetBounds(_vertexList);

                    var width = bounds.width == 0f ? 0f : 1f / bounds.width / Zoom;
                    var height = bounds.height == 0f ? 0f : 1f / bounds.height / Zoom;

                    if (ModifyVertices)
                    {
                        helper.Clear();

                        var radiusX = bounds.width / 2f;
                        var radiusY = bounds.height / 2f;
                        var centralVertex = new UIVertex();
                        centralVertex.position = Vector3.right * bounds.center.x + Vector3.up * bounds.center.y +
                                                 Vector3.forward * _vertexList[0].position.z;
                        centralVertex.normal = _vertexList[0].normal;
                        centralVertex.uv0 = new Vector2(0.5f, 0.5f);
                        centralVertex.color = Color.white;

                        var steps = 64;
                        for (var i = 0; i < steps; i++)
                        {
                            var curVertex = new UIVertex();
                            var angle = i * 360f / steps;
                            var cosX = Mathf.Cos(Mathf.Deg2Rad * angle);
                            var cosY = Mathf.Sin(Mathf.Deg2Rad * angle);

                            curVertex.position = Vector3.right * cosX * radiusX + Vector3.up * cosY * radiusY +
                                                 Vector3.forward * _vertexList[0].position.z;
                            curVertex.normal = _vertexList[0].normal;
                            curVertex.uv0 = new Vector2((cosX + 1) * 0.5f, (cosY + 1) * 0.5f);
                            curVertex.color = Color.white;
                            helper.AddVert(curVertex);
                        }

                        helper.AddVert(centralVertex);

                        for (var i = 1; i < steps; i++) helper.AddTriangle(i - 1, i, steps);
                        helper.AddTriangle(0, steps - 1, steps);
                    }

                    var vertex = new UIVertex();

                    for (var i = 0; i < helper.currentVertCount; i++)
                    {
                        helper.PopulateUIVertex(ref vertex, i);

                        vertex.color = BlendColor(vertex.color, EffectGradient.Evaluate(
                            Mathf.Sqrt(
                                Mathf.Pow(Mathf.Abs(vertex.position.x - bounds.center.x) * width, 2f) +
                                Mathf.Pow(Mathf.Abs(vertex.position.y - bounds.center.y) * height, 2f)) * 2f - Offset));

                        helper.SetUIVertex(vertex, i);
                    }
                }
                    break;
            }
        }

        private Rect GetBounds(List<UIVertex> vertices)
        {
            var left = vertices[0].position.x;
            var right = left;
            var bottom = vertices[0].position.y;
            var top = bottom;

            for (var i = vertices.Count - 1; i >= 1; --i)
            {
                var x = vertices[i].position.x;
                var y = vertices[i].position.y;

                if (x > right) right = x;
                else if (x < left) left = x;

                if (y > top) top = y;
                else if (y < bottom) bottom = y;
            }

            return new Rect(left, bottom, right - left, top - bottom);
        }

        private void SplitTrianglesAtGradientStops(List<UIVertex> _vertexList, Rect bounds, float zoomOffset,
            VertexHelper helper)
        {
            var stops = FindStops(zoomOffset, bounds);
            if (stops.Count > 0)
            {
                helper.Clear();

                var nCount = _vertexList.Count;
                for (var i = 0; i < nCount; i += 3)
                {
                    var positions = GetPositions(_vertexList, i);
                    var originIndices = new List<int>(3);
                    var starts = new List<UIVertex>(3);
                    var ends = new List<UIVertex>(2);

                    for (var s = 0; s < stops.Count; s++)
                    {
                        var initialCount = helper.currentVertCount;
                        var hadEnds = ends.Count > 0;
                        var earlyStart = false;

                        // find any start vertices for this stop
                        for (var p = 0; p < 3; p++)
                            if (!originIndices.Contains(p) && positions[p] < stops[s])
                            {
                                // make sure the first index crosses the stop
                                var p1 = (p + 1) % 3;
                                var start = _vertexList[p + i];
                                if (positions[p1] > stops[s])
                                {
                                    originIndices.Insert(0, p);
                                    starts.Insert(0, start);
                                    earlyStart = true;
                                }
                                else
                                {
                                    originIndices.Add(p);
                                    starts.Add(start);
                                }
                            }

                        // bail if all before or after the stop
                        if (originIndices.Count == 0)
                            continue;
                        if (originIndices.Count == 3)
                            break;

                        // report any start vertices
                        foreach (var start in starts)
                            helper.AddVert(start);

                        // make two ends, splitting at the stop
                        ends.Clear();
                        foreach (var index in originIndices)
                        {
                            var oppositeIndex = (index + 1) % 3;
                            if (positions[oppositeIndex] < stops[s])
                                oppositeIndex = (oppositeIndex + 1) % 3;
                            ends.Add(
                                CreateSplitVertex(_vertexList[index + i], _vertexList[oppositeIndex + i], stops[s]));
                        }

                        if (ends.Count == 1)
                        {
                            var oppositeIndex = (originIndices[0] + 2) % 3;
                            ends.Add(CreateSplitVertex(_vertexList[originIndices[0] + i],
                                _vertexList[oppositeIndex + i], stops[s]));
                        }

                        // report end vertices
                        foreach (var end in ends)
                            helper.AddVert(end);

                        // make triangles
                        if (hadEnds)
                        {
                            helper.AddTriangle(initialCount - 2, initialCount, initialCount + 1);
                            helper.AddTriangle(initialCount - 2, initialCount + 1, initialCount - 1);
                            if (starts.Count > 0)
                            {
                                if (earlyStart)
                                    helper.AddTriangle(initialCount - 2, initialCount + 3, initialCount);
                                else
                                    helper.AddTriangle(initialCount + 1, initialCount + 3, initialCount - 1);
                            }
                        }
                        else
                        {
                            var vertexCount = helper.currentVertCount;
                            helper.AddTriangle(initialCount, vertexCount - 2, vertexCount - 1);
                            if (starts.Count > 1)
                                helper.AddTriangle(initialCount, vertexCount - 1, initialCount + 1);
                        }

                        starts.Clear();
                    }

                    // clean up after looping through gradient stops
                    if (ends.Count > 0)
                    {
                        // find any final vertices after the gradient stops
                        if (starts.Count == 0)
                            for (var p = 0; p < 3; p++)
                                if (!originIndices.Contains(p) && positions[p] > stops[stops.Count - 1])
                                {
                                    var p1 = (p + 1) % 3;
                                    var end = _vertexList[p + i];
                                    if (positions[p1] > stops[stops.Count - 1])
                                        starts.Insert(0, end);
                                    else
                                        starts.Add(end);
                                }

                        // report final vertices
                        foreach (var start in starts)
                            helper.AddVert(start);

                        // make final triangle(s)
                        var vertexCount = helper.currentVertCount;
                        if (starts.Count > 1)
                        {
                            helper.AddTriangle(vertexCount - 4, vertexCount - 2, vertexCount - 1);
                            helper.AddTriangle(vertexCount - 4, vertexCount - 1, vertexCount - 3);
                        }
                        else if (starts.Count > 0)
                        {
                            helper.AddTriangle(vertexCount - 3, vertexCount - 1, vertexCount - 2);
                        }
                    }
                    else
                    {
                        // if the triangle wasn't split, add it as-is
                        helper.AddVert(_vertexList[i]);
                        helper.AddVert(_vertexList[i + 1]);
                        helper.AddVert(_vertexList[i + 2]);
                        var vertexCount = helper.currentVertCount;
                        helper.AddTriangle(vertexCount - 3, vertexCount - 2, vertexCount - 1);
                    }
                }
            }
        }

        private float[] GetPositions(List<UIVertex> _vertexList, int index)
        {
            var positions = new float[3];
            if (GradientType == Type.Horizontal)
            {
                positions[0] = _vertexList[index].position.x;
                positions[1] = _vertexList[index + 1].position.x;
                positions[2] = _vertexList[index + 2].position.x;
            }
            else
            {
                positions[0] = _vertexList[index].position.y;
                positions[1] = _vertexList[index + 1].position.y;
                positions[2] = _vertexList[index + 2].position.y;
            }

            return positions;
        }

        private List<float> FindStops(float zoomOffset, Rect bounds)
        {
            var stops = new List<float>();
            var offset = Offset * (1 - zoomOffset);
            var startBoundary = zoomOffset - offset;
            var endBoundary = 1 - zoomOffset - offset;

            foreach (var color in EffectGradient.colorKeys)
            {
                if (color.time >= endBoundary)
                    break;
                if (color.time > startBoundary)
                    stops.Add((color.time - startBoundary) * Zoom);
            }

            foreach (var alpha in EffectGradient.alphaKeys)
            {
                if (alpha.time >= endBoundary)
                    break;
                if (alpha.time > startBoundary)
                    stops.Add((alpha.time - startBoundary) * Zoom);
            }

            var min = bounds.xMin;
            var size = bounds.width;
            if (GradientType == Type.Vertical)
            {
                min = bounds.yMin;
                size = bounds.height;
            }

            stops.Sort();
            for (var i = 0; i < stops.Count; i++)
            {
                stops[i] = stops[i] * size + min;

                if (i > 0 && Math.Abs(stops[i] - stops[i - 1]) < 2)
                {
                    stops.RemoveAt(i);
                    --i;
                }
            }

            return stops;
        }

        private UIVertex CreateSplitVertex(UIVertex vertex1, UIVertex vertex2, float stop)
        {
            if (GradientType == Type.Horizontal)
            {
                var sx = vertex1.position.x - stop;
                var dx = vertex1.position.x - vertex2.position.x;
                var dy = vertex1.position.y - vertex2.position.y;
                var uvx = vertex1.uv0.x - vertex2.uv0.x;
                var uvy = vertex1.uv0.y - vertex2.uv0.y;
                var ratio = sx / dx;
                var splitY = vertex1.position.y - dy * ratio;

                var splitVertex = new UIVertex();
                splitVertex.position = new Vector3(stop, splitY, vertex1.position.z);
                splitVertex.normal = vertex1.normal;
                splitVertex.uv0 = new Vector2(vertex1.uv0.x - uvx * ratio, vertex1.uv0.y - uvy * ratio);
                splitVertex.color = Color.white;
                return splitVertex;
            }
            else
            {
                var sy = vertex1.position.y - stop;
                var dy = vertex1.position.y - vertex2.position.y;
                var dx = vertex1.position.x - vertex2.position.x;
                var uvx = vertex1.uv0.x - vertex2.uv0.x;
                var uvy = vertex1.uv0.y - vertex2.uv0.y;
                var ratio = sy / dy;
                var splitX = vertex1.position.x - dx * ratio;

                var splitVertex = new UIVertex();
                splitVertex.position = new Vector3(splitX, stop, vertex1.position.z);
                splitVertex.normal = vertex1.normal;
                splitVertex.uv0 = new Vector2(vertex1.uv0.x - uvx * ratio, vertex1.uv0.y - uvy * ratio);
                splitVertex.color = Color.white;
                return splitVertex;
            }
        }

        private Color BlendColor(Color colorA, Color colorB)
        {
            switch (BlendMode)
            {
                default: return colorB;
                case Blend.Add: return colorA + colorB;
                case Blend.Multiply: return colorA * colorB;
            }
        }

        #region Properties

        public Blend BlendMode
        {
            get => _blendMode;
            set
            {
                _blendMode = value;
                graphic.SetVerticesDirty();
            }
        }

        public UnityEngine.Gradient EffectGradient
        {
            get => _effectGradient;
            set
            {
                _effectGradient = value;
                graphic.SetVerticesDirty();
            }
        }

        public Type GradientType
        {
            get => _gradientType;
            set
            {
                _gradientType = value;
                graphic.SetVerticesDirty();
            }
        }

        public bool ModifyVertices
        {
            get => _modifyVertices;
            set
            {
                _modifyVertices = value;
                graphic.SetVerticesDirty();
            }
        }

        public float Offset
        {
            get => _offset;
            set
            {
                _offset = Mathf.Clamp(value, -1f, 1f);
                graphic.SetVerticesDirty();
            }
        }

        public float Zoom
        {
            get => _zoom;
            set
            {
                _zoom = Mathf.Clamp(value, 0.1f, 10f);
                graphic.SetVerticesDirty();
            }
        }

        #endregion
    }
}