using System.Collections.Generic;
using JNGame.Math;

namespace JNGame.PathFinding
{
    /// <summary>
    /// 二叉空间分割树节点
    /// </summary>
    public partial class BspTreeNode
    {
        /// <summary>
        /// 划分到三角形数小于此则停止，可以性能测试下，选择一个合适的值
        /// </summary>
        private const int kMinTriangleCount = 3;

        /// <summary>
        /// 找到树叶节点，向上取三层，获取包含的三角形，用于查找落位阻挡点的临近三角形
        /// </summary>
        private const int kNearestDeepSearch = 3;

        /// <summary>
        /// 当前节点中包含的三角形数据
        /// </summary>
        public List<TriangleRef> tris;
        /// <summary>
        /// 当前节点的子节点
        /// </summary>
        private BspTreeNode[] m_Children;
        /// <summary>
        /// 当前节点的树深
        /// </summary>
        public int depth = 0;
        /// <summary>
        /// 节点的切割线
        /// </summary>
        public SplitLine splitLine;
        /// <summary>
        /// 是否是叶子节点
        /// </summary>
        public bool IsLeaf => m_Children == null;
        /// <summary>
        /// 左子树
        /// </summary>
        public BspTreeNode LeftChild => m_Children?[0];
        /// <summary>
        /// 右子树
        /// </summary>
        public BspTreeNode RightChild => m_Children?[1];

        /// <summary>
        /// 获取指定坐标所在的三角形索引
        /// </summary>
        /// <param name="pos"></param>
        /// <returns></returns>
        public int GetTriangle(in LVector2 pos, out int searchDeep, out List<TriangleRef> triangeGroup)
        {
            if (IsLeaf)
            {
                searchDeep = -1;
                triangeGroup = null;
                foreach (var tri in tris)
                {
                    if (tri.Contain(pos))
                    {
                        return tri.index;
                    }
                }
                searchDeep = kNearestDeepSearch;
                return -1;
            }
            else
            {
                var isLeft = LVector2.Cross(splitLine.vertexB - splitLine.vertexA, pos - splitLine.vertexA) >= 0;
                if (isLeft)
                {
                    int targetIndex = LeftChild.GetTriangle(pos, out searchDeep, out triangeGroup);
                    if (targetIndex == -1)
                    {
                        --searchDeep;
                        if (searchDeep == 0)
                        {
                            triangeGroup = tris;
                        }
                    }
                    return targetIndex;
                }
                else
                {
                    int targetIndex = RightChild.GetTriangle(pos, out searchDeep, out triangeGroup);
                    if (targetIndex == -1)
                    {
                        --searchDeep;
                        if (searchDeep == 0)
                        {
                            triangeGroup = tris;
                        }
                    }
                    return targetIndex;
                }
            }
        }

        /// <summary>
        /// 初始化二叉空间树的节点
        /// </summary>
        /// <param name="tris"></param>
        /// <param name="depth"></param>
        public void Init(List<TriangleRef> tris, int depth = 0)
        {
            this.depth = depth;
            this.tris = tris;

            if (tris.Count <= kMinTriangleCount)
            { // 三角形数少于指标，停止
                return;
            }
            if (depth > 20)
            { // 树深超过20层，停止
                return;
            }
            // 选择分割线
            splitLine = PickSplitLine(tris);
            m_Children = new BspTreeNode[] { new BspTreeNode(), new BspTreeNode() };
            var lTris = new List<TriangleRef>();
            var rTris = new List<TriangleRef>();
            foreach (var tri in tris)
            {
                var val = SplitLine.GetSplitResult(in splitLine, tri);
                if (val == EnumSplitType.Left)
                { // 三角形位于切割线左侧，加入左子树三角形列表
                    lTris.Add(tri);
                }
                else if (val == EnumSplitType.Right)
                { // 三角形位于切割线右侧，加入右子树三角形列表
                    rTris.Add(tri);
                }
                else
                { // 切割线经过三角形，将三角形分为几个多边形
                    SplitTriangle(lTris, rTris, tri);
                }
            }

            LeftChild.Init(lTris, depth + 1);
            RightChild.Init(rTris, depth + 1);
        }

        private readonly List<LVector2> m_RightVerts = new List<LVector2>();
        private readonly List<LVector2> m_LeftVerts = new List<LVector2>();

        /// <summary>
        /// 将三角形按切割线切割为若干个三角形
        /// </summary>
        /// <param name="lTris"></param>
        /// <param name="rTris"></param>
        /// <param name="tri"></param>
        private void SplitTriangle(List<TriangleRef> lTris, List<TriangleRef> rTris, TriangleRef tri)
        {
            int numVerts = 3;
            m_RightVerts.Clear();
            m_LeftVerts.Clear();
            var a = tri[2];
            var aSide = SplitLine.ClassifyPointToPlane(splitLine, a);
            for (int i = 0; i < numVerts; i++)
            {
                var b = tri[i];
                var bSide = SplitLine.ClassifyPointToPlane(splitLine, b);
                if (bSide == EnumSplitType.Right)
                {
                    if (aSide == EnumSplitType.Left)
                    {
                        var p = SplitLine.GetIntersectPoint(a, b, splitLine.vertexA, splitLine.vertexB);
                        m_RightVerts.Add(p);
                        m_LeftVerts.Add(p);
                    }
                    else if (aSide == EnumSplitType.OnPlane)
                    {
                        if (m_RightVerts.Count == 0 || a != m_RightVerts[m_RightVerts.Count - 1])
                        {
                            m_RightVerts.Add(a);
                        }
                    }

                    m_RightVerts.Add(b);
                }
                else if (bSide == EnumSplitType.Left)
                {
                    if (aSide == EnumSplitType.Right)
                    {
                        var p = SplitLine.GetIntersectPoint(a, b, splitLine.vertexA, splitLine.vertexB);
                        m_RightVerts.Add(p);
                        m_LeftVerts.Add(p);
                    }
                    else if (aSide == EnumSplitType.OnPlane)
                    {
                        if (m_LeftVerts.Count == 0 || a != m_LeftVerts[m_LeftVerts.Count - 1])
                        {
                            m_LeftVerts.Add(a);
                        }
                    }

                    m_LeftVerts.Add(b);
                }
                else
                {
                    if (aSide == EnumSplitType.Right)
                    {
                        if (!(m_RightVerts.Count == 3 && b == m_RightVerts[0]))
                        {
                            m_RightVerts.Add(b);
                        }
                    }
                    else if (aSide == EnumSplitType.Left)
                    {
                        if (!(m_LeftVerts.Count == 3 && b == m_LeftVerts[0]))
                        {
                            m_LeftVerts.Add(b);
                        }
                    }
                }

                a = b;
                aSide = bSide;
            }

            //push into tri list
            if (m_LeftVerts.Count >= 3)
            {
                if (m_LeftVerts.Count == 3)
                {
                    AddTriangle(lTris, m_LeftVerts[0], m_LeftVerts[1], m_LeftVerts[2], tri);
                }
                else
                {
                    // Debug.Assert(m_LeftVerts.Count == 4);
                    AddTriangle(lTris, m_LeftVerts[0], m_LeftVerts[1], m_LeftVerts[2], tri);
                    AddTriangle(lTris, m_LeftVerts[0], m_LeftVerts[2], m_LeftVerts[3], tri);
                }
            }

            if (m_RightVerts.Count >= 3)
            {
                if (m_RightVerts.Count == 3)
                {
                    AddTriangle(rTris, m_RightVerts[0], m_RightVerts[1], m_RightVerts[2], tri);
                }
                else
                {
                    // Debug.Assert(m_RightVerts.Count == 4);
                    AddTriangle(rTris, m_RightVerts[0], m_RightVerts[1], m_RightVerts[2], tri);
                    AddTriangle(rTris, m_RightVerts[0], m_RightVerts[2], m_RightVerts[3], tri);
                }
            }
        }

        private void AddTriangle(List<TriangleRef> triangles, in LVector2 vertexA, in LVector2 vertexB, in LVector2 vertexC, TriangleRef tri)
        {
            if (vertexA == vertexB || vertexB == vertexC || vertexC == vertexA) { return; }
            triangles.Add(new TriangleRef(vertexA, vertexB, vertexC, tri));
        }

        /// <summary>
        /// 选择一条合适的切割线
        /// </summary>
        /// <param name="tris">待切割的三角形集合</param>
        /// <returns></returns>
        private static SplitLine PickSplitLine(List<TriangleRef> tris)
        {
            int minScore = int.MinValue;
            int minLCount = 0;
            int minRCount = 0;
            SplitLine bestLine = new SplitLine();
            int[] splitCounter = new int[(int)EnumSplitType.EnumCount]; // 每次切割，三角形位于切割线左右和线上的次数统计
            var tirCount = tris.Count;
            foreach (var tri in tris)
            { // 遍历所有三角形的边框线，作为切割线来切割空间，计算每次切割的分数，从而选取最优的分割线
                foreach (var borderLine in tri.borders)
                {
                    for (int i = 0; i < (int)EnumSplitType.EnumCount; i++)
                    {
                        splitCounter[i] = 0;
                    }
                    foreach (var otherTri in tris)
                    {
                        var val = (int)SplitLine.GetSplitResult(borderLine, otherTri);
                        splitCounter[val]++;
                    }

                    // Clock wise =>Left ++   CCW=>Right++// self tri is on the left
                    var leftCount = splitCounter[(int)EnumSplitType.Left];
                    var rightCount = splitCounter[(int)EnumSplitType.Right];
                    var splitCount = splitCounter[(int)EnumSplitType.OnPlane];
                    if ((leftCount == 0 || rightCount == 0) && (leftCount + rightCount) == tirCount)
                    {
                        // 所有的三角形都在同一侧，忽略
                        continue;
                    }
                    // 根据切割线左右的三角形数，以及切割的三角形数，计算本次分割的得分
                    var balanceVal = LMath.Abs(leftCount - rightCount);
                    var sameVal = LMath.Min(leftCount, rightCount);
                    int score = sameVal * 3 - balanceVal - splitCount * 2;
                    if (score > minScore)
                    { // 选取得分最高的作为切割线
                        minLCount = leftCount;
                        minRCount = rightCount;
                        minScore = score;
                        bestLine = borderLine;
                    }
                }
            }

            return bestLine;
        }
    }
}