#version 430 core

#define FAR_CLIP  10000.0f
#define width 1080
#define height 720

struct Triangle
{
    vec3 vA, vB, vC;
};
struct Light{
    vec4    dir;
    vec4    color;
    vec4    attenuation;
};
struct Primitive{
    vec4 A, B, C;
};
struct Camera{
    vec3    pos, dir, yAxis, xAxis ;
    float   tanFovY, tanFovX;
};
struct Ray{
    vec3    origin;
    vec3    dir;
};

layout(binding = 0, rgba32f) uniform image2D framebuffer;
layout(std430, binding = 1) buffer meshtriangles
 {
    Triangle tris[ ];
 };

uniform int mNumTriangles;
uniform sampler2D diffuse;
uniform Camera camera;
Light light;





float hitTriangle(Ray r, Primitive t)
{
    vec3 AB = t.B.xyz - t.A.xyz;
    vec3 AC = t.C.xyz - t.A.xyz;

    float det = determinant( mat3(AB, AC, -1.0f*r.dir) );

    if(det == 0.0f){
        return FAR_CLIP;
    } else {
        vec3 oA = r.origin - t.A.xyz;

        mat3 Di = inverse(mat3(AB, AC, -1.0f*r.dir));
        vec3 solution = Di*oA;

        if(solution.x >= -0.0001 && solution.x <= 1.0001){
            if(solution.y >= -0.0001 && solution.y <= 1.0001){
                if(solution.x + solution.y <= 1.0001){
                    return solution.z;
                }
            }
        }
        return FAR_CLIP;
    }
}


Ray initRay(uint x, uint y, Camera cam){
    Ray r;
    vec3 dir;
    float a, b, halfWidth, halfHeight;

    halfWidth = float(width)/2.0f;
    halfHeight = float(height)/2.0f;

    a = cam.tanFovX*( (float(x)-halfWidth+0.5f) / halfWidth);
    b = cam.tanFovY*( (halfHeight - float(y)-0.5f) / halfHeight);

    dir = normalize( a*cam.xAxis.xyz + b*cam.yAxis.xyz + cam.dir.xyz);

    r.dir = dir;
    r.origin = cam.pos.xyz;

    return r;
}

layout (local_size_x = 25, local_size_y = 8) in;
void main(void) {
    uint x = gl_GlobalInvocationID.x;
    uint y = gl_GlobalInvocationID.y;

    //Hardcoded light values
    light.dir = vec4(0, -1, 0, 0);
    light.color = vec4(1, 1, 1, 1);
    light.attenuation = vec4(1.0f);


    if(x < width && y < height)
    {

        //Color used to find out the final color.
        vec4 color = vec4(0.0f, 0.0f, 0.0f, 1.0f);
        vec4 tempColor = vec4(0);

        //Initialize the pixel/camera ray.
        Ray r = initRay(x, y, camera);

        float t = FAR_CLIP, temp = FAR_CLIP;
        int currentObject = -1;
        for(int i = 0; i < mNumTriangles; i++)
        {

            Primitive t0;
            t0.A = vec4(tris[i].vA, 1);
            t0.B =  vec4(tris[i].vB, 1);
            t0.C =  vec4(tris[i].vC, 1);
            //Basically if it finds something, it'll return something thats not FAR_CLIP
            temp = hitTriangle(r, t0);

            //If the ray hit something, then we need to shade it. Just  give it a color for now.
            if(temp != t)
            {
                color = vec4(0, 1, 0,1);
                t = temp;
                currentObject = i;
            }
        }



        imageStore(framebuffer, ivec2(x, y), color);

    }
}