using System.Collections;
using System.Collections.Generic;
using UnityEngine;

namespace BITKit.Physics
{
    public static class GeometryUtils
    {
        /// <summary>
        /// 获取一个点到一条线段的最近点
        /// </summary>
        /// <param name="point"></param>
        /// <param name="lineStart"></param>
        /// <param name="lineEnd"></param>
        /// <returns></returns>
        public static Vector3 PointToLineSegmentDistance(Vector3 point, Vector3 lineStart, Vector3 lineEnd)
        {
            Vector3 lineDirection = lineEnd - lineStart;
            Vector3 pointDirection = point - lineStart;
 
            float lineLength = lineDirection.magnitude;
            lineDirection.Normalize();
 
            float dotProduct = Vector3.Dot(pointDirection, lineDirection);
            dotProduct = Mathf.Clamp(dotProduct, 0f, lineLength);
 
            Vector3 closestPoint = lineStart + lineDirection * dotProduct;
            return closestPoint;
        }
        /// <summary>
        /// 获取一个点到一个三角形内最短距离的点
        /// </summary>
        /// <param name="a">三角形顶点a</param>
        /// <param name="b">三角形顶点b</param>
        /// <param name="c">三角形顶点c</param>
        /// <param name="pos"></param>
        /// <returns></returns>
        public static Vector3 GetPosInTriangle(Vector3 a, Vector3 b, Vector3 c, Vector3 pos)
        {
            Vector3 normal = Vector3.Cross(b - a, c - a).normalized;
            Vector3 toPoint = pos - a;
            float distance = Vector3.Dot(toPoint, normal);
 
            Vector3 targetPos = pos - distance * normal;
 
            if(PointInTriangle(targetPos, a, b, c))
                return targetPos;
            else
            {
                Vector3 p1 = PointToLineSegmentDistance(pos, a, b);
                Vector3 p2 = PointToLineSegmentDistance(pos, a, c);
                Vector3 p3 = PointToLineSegmentDistance(pos, b, c);
 
                float d1 = Vector3.Distance(p1, pos);
                float d2 = Vector3.Distance(p2, pos);
                float d3 = Vector3.Distance(p3, pos);
 
                if (d1 <= d2 && d1 <= d3)
                    return p1;
                else if (d2 <= d3 && d2 <= d1)
                    return p2;
                else /*if(d3 <= d1 && d3 <= d2)*/
                    return p3;
 
                //return default;
            }
        }
 
        /// <summary>
        /// 判断一个点是否在三角形内
        /// </summary>
        /// <param name="pos"></param>
        /// <param name="a"></param>
        /// <param name="b"></param>
        /// <param name="c"></param>
        /// <returns></returns>
        public static bool PointInTriangle(Vector3 pos, Vector3 a, Vector3 b, Vector3 c)
        {
            var v0 = c - a;
            var v1 = b - a;
            var v2 = pos - a;
 
            var dot00 = Vector3.Dot(v0, v0);
            var dot01 = Vector3.Dot(v0, v1);
            var dot02 = Vector3.Dot(v0, v2);
            var dot11 = Vector3.Dot(v1, v1);
            var dot12 = Vector3.Dot(v1, v2);
 
            var invDenom = 1 / (dot00 * dot11 - dot01 * dot01);
            var u = (dot11 * dot02 - dot01 * dot12) * invDenom;
            var v = (dot00 * dot12 - dot01 * dot02) * invDenom;
 
            // 如果u和v都在[0,1]的范围内，那么点P在三角形ABC内
            return (u >= 0) && (v >= 0) && (u + v < 1);
        }
    }

}