using JNGame.Math;

namespace JNGame.PathFinding
{
    /// <summary>
    /// 二叉空间树的切割线
    /// </summary>
    public struct SplitLine
    {
        /// <summary>
        /// 切割线起点
        /// </summary>
        public LVector2 vertexA;
        /// <summary>
        /// 切割线终点
        /// </summary>
        public LVector2 vertexB;
        /// <summary>
        /// 切割线方向
        /// </summary>
        public readonly LVector2 Direction => vertexB - vertexA;

        /// <summary>
        /// 构造切割线
        /// </summary>
        /// <param name="vertexA"></param>
        /// <param name="vertexB"></param>
        public SplitLine(in LVector2 vertexA, in LVector2 vertexB)
        {
            this.vertexA = vertexA;
            this.vertexB = vertexB;
        }

        /// <summary>
        /// 获取三角形的切割结果
        /// </summary>
        /// <param name="line">切割线</param>
        /// <param name="tri">切割三角形</param>
        /// <returns>切割线左侧、右侧或经过切割线</returns>
        public static EnumSplitType GetSplitResult(in SplitLine line, TriangleRef tri)
        {
            var lineDir = line.Direction;
            // 三角形三个顶点与切割线的位置关系
            var valA = LVector2.Cross(lineDir, tri.vertexA - line.vertexA);
            var valB = LVector2.Cross(lineDir, tri.vertexB - line.vertexA);
            var valC = LVector2.Cross(lineDir, tri.vertexC - line.vertexA);

            var isRight = false;
            if (valA != 0) isRight = valA < 0;
            if (valB != 0) isRight = valB < 0;
            if (valC != 0) isRight = valC < 0;

            var isA = valA <= 0;
            var isB = valB <= 0;
            var isC = valC <= 0;
            if (isA == isB && isB == isC)
            {
                return isRight ? EnumSplitType.Right : EnumSplitType.Left;
            }

            isA = valA >= 0;
            isB = valB >= 0;
            isC = valC >= 0;
            if (isA == isB && isB == isC)
            {
                return isRight ? EnumSplitType.Right : EnumSplitType.Left;
            }

            return EnumSplitType.OnPlane;
        }

        /// <summary>
        /// 获取顶点和切割线的位置关系
        /// </summary>
        /// <param name="line">切割线</param>
        /// <param name="vertex">顶点</param>
        /// <returns></returns>
        public static EnumSplitType ClassifyPointToPlane(in SplitLine line, in LVector2 vertex)
        {
            var val = LVector2.Cross(line.Direction, vertex - line.vertexA);
            if (val == 0)
            {
                return EnumSplitType.OnPlane;
            }
            else
            {
                return val < 0 ? EnumSplitType.Right : EnumSplitType.Left;
            }
        }

        /// <summary>
        /// 计算p0p1,p2p3的交点
        /// </summary>
        /// <param name="p0"></param>
        /// <param name="p1"></param>
        /// <param name="p2"></param>
        /// <param name="p3"></param>
        /// <returns></returns>
        public static LVector2 GetIntersectPoint(in LVector2 p0, in LVector2 p1, in LVector2 p2, in LVector2 p3)
        {
            var diff = p2 - p0;
            var d1 = p1 - p0;
            var d2 = p3 - p2;
            var demo = LMath.Cross(d1, d2); //det
            if (LMath.Abs(demo) < LFloat.EPSILON)
            {
                // 叉积结果为0，说明两个向量平行
                return p0;
            }

            var t1 = LMath.Cross(diff, d2) / demo; // Cross2D(diff,-d2)
            return p0 + (p1 - p0) * t1;
        }
    }
}