using System;
// using JNGame.Collision2D;
using JNGame.Math;
// using Debug = JNGame.Logging.Debug;

namespace JNGame.PathFinding
{
    /// <summary>
    /// 导航三角形在二叉空间分割树中的引用
    /// <para>一个导航三角形可能会被树分割为多个三角形引用</para>
    /// </summary>
    public class TriangleRef
    {
        /// <summary>
        /// 当前三角形引用关联的导航三角形索引
        /// </summary>
        public int index;
        /// <summary>
        /// 三角形顶点A
        /// </summary>
        public LVector2 vertexA;
        /// <summary>
        /// 三角形顶点B
        /// </summary>
        public LVector2 vertexB;
        /// <summary>
        /// 三角形顶点C
        /// </summary>
        public LVector2 vertexC;

        /// <summary>
        /// 是否是分割的三角形
        /// </summary>
        public bool IsSplit { get; private set; } = false;
        /// <summary>
        /// 三角形的边框
        /// </summary>
        public SplitLine[] borders;

        /// <summary>
        /// 根据下标获取三角形的顶点，合法下标0/1/2
        /// </summary>
        /// <param name="index"></param>
        /// <returns></returns>
        /// <exception cref="IndexOutOfRangeException"></exception>
        public LVector2 this[int index]
        {
            get
            {
                return index switch
                {
                    0 => vertexA,
                    1 => vertexB,
                    2 => vertexC,
                    _ => throw new IndexOutOfRangeException("vector idx invalid" + index),
                };
            }
        }

        /// <summary>
        /// 根据原始导航三角形创建引用
        /// <para>由此构造的三角形引用认为是未切割过的三角形</para>
        /// </summary>
        /// <param name="srcTriangle">原始的导航三角形</param>
        public TriangleRef(NavTriangle srcTriangle)
            : this(srcTriangle.vertexA.ToLVector2XZ(), srcTriangle.vertexB.ToLVector2XZ(), srcTriangle.vertexC.ToLVector2XZ(), srcTriangle.index)
        { }

        /// <summary>
        /// 根据分割的三个顶点和原始导航三角形创建引用
        /// <para>由此构造的三角形引用认为是切割过的三角形</para>
        /// </summary>
        /// <param name="vertexA">三角形顶点A</param>
        /// <param name="vertexB">三角形顶点B</param>
        /// <param name="vertexC">三角形顶点C</param>
        /// <param name="srcTriangle">原始的导航三角形</param>
        public TriangleRef(in LVector2 vertexA, in LVector2 vertexB, in LVector2 vertexC, TriangleRef srcTriangle)
            : this(vertexA, vertexB, vertexC, srcTriangle.index)
        {
            IsSplit = true;
        }

        /// <summary>
        /// 私有构造
        /// </summary>
        /// <param name="vertexA">三角形顶点A</param>
        /// <param name="vertexB">三角形顶点B</param>
        /// <param name="vertexC">三角形顶点C</param>
        /// <param name="idx">引用的导航三角形索引</param>
        private TriangleRef(in LVector2 vertexA, in LVector2 vertexB, in LVector2 vertexC, int idx)
        {
            this.vertexA = vertexA;
            this.vertexB = vertexB;
            this.vertexC = vertexC;
            index = idx;
            borders = new SplitLine[]
            {
                new SplitLine(vertexA, vertexB),
                new SplitLine(vertexB, vertexC),
                new SplitLine(vertexC, vertexA)
            };
            //check valid 
            CheckValid();
        }

        /// <summary>
        /// 三角形三点不可重合
        /// </summary>
        private void CheckValid()
        {
            for (int i = 0; i < 3; i++)
            {
                if (borders[i].Direction == LVector2.Zero)
                {
                    // Debug.Assert(false);
                }
            }
        }

        /// <summary>
        /// 判断点是否在此三角形内
        /// </summary>
        /// <param name="pos"></param>
        /// <returns></returns>
        public bool Contain(in LVector2 pos)
        {
            // ABC三个顶点绕序为顺时针，三个叉积都需要为负，则点在三角形内
            var isRightA = LVector2.Cross(vertexB - vertexA, pos - vertexA) > 0;
            if (isRightA) return false;
            var isRightB = LVector2.Cross(vertexC - vertexB, pos - vertexB) > 0;
            if (isRightB) return false;
            var isRightC = LVector2.Cross(vertexA - vertexC, pos - vertexC) > 0;
            if (isRightC) return false;
            return true;
        }
    }
}