/// Copyright (c) 2021 Iiro Iivanainen, Harri Linna, Jere Pakkanen, Riikka Vilavaara
/// 
/// Permission is hereby granted, free of charge, to any person obtaining
/// a copy of this software and associated documentation files (the
/// "Software"), to deal in the Software without restriction, including
/// without limitation the rights to use, copy, modify, merge, publish,
/// distribute, sublicense, and/or sell copies of the Software, and to
/// permit persons to whom the Software is furnished to do so, subject to
/// the following conditions:
/// 
/// The above copyright notice and this permission notice shall be included
/// in all copies or substantial portions of the Software.
/// 
/// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
/// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
/// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
/// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
/// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
/// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
/// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

using System;
using System.Numerics;

namespace WPFOpenGL
{
    public static class RayCast
    {
        public static bool IntersectPlane(Vector3 rayOrigin, Vector3 rayDirection, Vector3 planeCenter, Vector3 planeNormal, out Vector3 hit, out float distance, bool backculling)
        {
            rayOrigin = MathHelper.RotateX(rayOrigin, MathHelper.DegreesToRadians(-MainWindow.eulerAngle.X));
            rayOrigin = MathHelper.RotateY(rayOrigin, MathHelper.DegreesToRadians(-MainWindow.eulerAngle.Y));
            rayOrigin = MathHelper.RotateZ(rayOrigin, MathHelper.DegreesToRadians(-MainWindow.eulerAngle.Z));

            float epsilon = 1E-6f;
            hit = Vector3.Zero;
            distance = float.MaxValue;

            float denom = Vector3.Dot(planeNormal, rayDirection);
            if (denom > epsilon || (backculling && denom < -epsilon))
            {
                Vector3 p0r0 = planeCenter - rayOrigin; 
                distance = Vector3.Dot(p0r0, planeNormal) / denom;
                hit = rayOrigin + (distance * rayDirection);
                return true;
            }
            
            return false;
        }

        public static bool IntersectQuad(Vector3 rayOrigin, Vector3 rayDirection, Vector3 v0, Vector3 v1, Vector3 v2, Vector3 v3, out Vector3 hit, out float distance)
        {
            if (IntersectTriangle(rayOrigin, rayDirection, v0, v1, v2, out hit, out distance))
            {
                return true;
            }
            if (IntersectTriangle(rayOrigin, rayDirection, v1, v2, v3, out hit, out distance))
            {
                return true;
            }
            return false;
        }

        public static bool IntersectTriangle(Vector3 rayOrigin, Vector3 rayDirection, Vector3 v0, Vector3 v1, Vector3 v2, out Vector3 hit, out float distance)
        {
            rayOrigin = MathHelper.RotateX(rayOrigin, MathHelper.DegreesToRadians(-MainWindow.eulerAngle.X));
            rayOrigin = MathHelper.RotateY(rayOrigin, MathHelper.DegreesToRadians(-MainWindow.eulerAngle.Y));
            rayOrigin = MathHelper.RotateZ(rayOrigin, MathHelper.DegreesToRadians(-MainWindow.eulerAngle.Z));

            Vector3 v0v1 = v1 - v0;
            Vector3 v0v2 = v2 - v0;
            Vector3 pvec = Vector3.Cross(rayDirection, v0v2); 
            float det = Vector3.Dot(v0v1, pvec); 

            float epsilon = 1E-6f;
            hit = new Vector3();
            distance = float.MaxValue;

            //if (det < kEpsilon) return false; 
            if (MathF.Abs(det) < epsilon) return false; 
            float invDet = 1f / det;
        
            Vector3 tvec = rayOrigin - v0;
            float u = Vector3.Dot(tvec, pvec) * invDet;
            if (u < 0 || u > 1) return false;
        
            Vector3 qvec = Vector3.Cross(tvec, v0v1);
            float v = Vector3.Dot(rayDirection, qvec) * invDet;
            if (v < 0 || u + v > 1) return false;
        
            distance = Vector3.Dot(v0v2, qvec) * invDet;
            hit = rayOrigin + distance * rayDirection;
        
            return true;
        }
    }
}