layout(local_size_x = 64​, local_size_y = 1​, local_size_z = 1​) in;

#define NO_CHILDREN 0xFFFFFFFF
#define GREY_VEC vec3(0.33333,0.33333,0.33333)
struct CellPosition {
    uint children[8];
};


layout(set=0,binding=1,std430) buffer CellPositions {
    CellPosition data[];
} cell_positions;

struct CellMaterial {
    uint position; // xyz 10 bits
    uint albedo; //rgb albedo
    uint emission; //rgb normalized with e as multiplier
    uint normal; //RGB normal encoded
    uint level_alpha;
};

layout(set=0,binding=1,std430) buffer CellMaterials {
    CellMaterial data[];
} cell_materials;

#define LIGHT_TYPE_DIRECTIONAL 0
#define LIGHT_TYPE_OMNI 1
#define LIGHT_TYPE_SPOT 2

struct Light {

    uint type;
    float energy;
    float radius;
    float attenuation;

    vec4 color;

    float radius;
    float attenuation;
    float spot_angle_radians;

    vec3 position;
    float spot_attenuation;

    float advance;
    float max_length;

    vec3 direction;
    bool visible;


    vec4 color;

    vec4 clip_planes[3];
};

layout(set=0,binding=1,std430) buffer Lights {
    Light data[];
} lights;


layout(set=0,binding=1,std430) uniform Params {
    vec3 limits;
    uint size;
    uint stack_size;
    uint light_count;
    float emission_scale;
} params;


uint raymarch(float distance,float distance_adv,vec3 from,vec3 direction) {

    uint result = NO_CHILDREN;

    while (distance > -distance_adv) { //use this to avoid precision errors

        uint32_t cell = 0;

        ivec3 pos = ivec3(from);
        ivec3 ofs = ivec3(0);
        ivec3 half = ivec3(params.size) / 2;
        if (any(lessThan(pos,ivec3(0))) || any(greaterThanEqual(pos,ivec3(params.size)))) {
            return NO_CHILDREN; //outside range
        }

        for (int i = 0; i < params.stack_size - 1; i++) {

            bvec3 greater = greaterThanEqual(pos,ofs+half);

            ofs += mix(ivec3(0),half,greater);

            uint child = 0; //wonder if this can be done faster
            if (greater.x) {
                child|=1;
            }
            if (greater.y) {
                child|=2;
            }
            if (greater.z) {
                child|=4;
            }

            cell = cell_positions.data[child];
            if (cell == NO_CHILDREN)
                break;

            half >>= ivec3(1);
        }

        if ( cell != NO_CHILDREN) {
            return cell; //found cell!
        }

        from += direction * distance_adv;
        distance -= distance_adv;
    }

    return NO_CHILDREN;
}

bool compute_light_vector(uint light,uint cell, vec3 pos,out float attenuation, out vec3 light_pos) {

    if (lights.data[light].type==LIGHT_TYPE_DIRECTIONAL) {

        vec4 normal = unpackSnorm4x8(cell_materials.data[cell].normal).xyz;

        if (normal.z < 0.5 && dot(normal,lights.data[light].direction) >=0.0 ) {
            //not omni-normal and
            return false;
        }

        float max_len = params.max_length;
        //TODO clip "to" by planes
        light_pos = lights.data[light].direction * params.max_length;
        attenuation = 1.0;

    } else {

        light_pos = lights.data[light].position;
        float distance = length(pos - light_pos);
        if (distance >= lights.data[light].radius) {
            return false;
        }

        attenuation = pow( distance / lights.data[light].radius + 0.0001, lights.data[light].attenuation );


        if (lights.data[light].type==LIGHT_TYPE_SPOT) {

            vec3 rel = normalize(pos - light_pos);
            float angle = acos(dot(rel,lights.data[light].direction));
            if (angle > lights.data[light].spot_angle_radians) {
                return false;
            }

            float d = clamp(angle / lights.data[light].spot_angle_radians, 0, 1);
            attenuation *= powf(1.0 - d, lights.data[light].spot_attenuation);
        }
    }

    return true;
}

void main() {

    uint cell_index = gl_GlobalInvocationID.x;

    vec3 pos = vec3(ivec3(cells.data[cell_index].position&0x3FF,(cells.data[cell_index].position>>10)&0x3FF,cells.data[cell_index].position>>20));
    float distance_adv = lights.data[light].advance;

    vec3 emission = vec3(ivec3(cells.data[cell_index].emission&0x3FF,(cells.data[cell_index].emission>>10)&0x7FF,cells.data[cell_index].emission>>21)) * params.emission_scale;
    vec3 albedo = unpackUnorm4x8(cells.data[cell_index].albedo).rgb;
    vec4 normal = unpackSnorm4x8(cells.data[cell_index].normal); //w >0.5 means, all directions

#ifdef MODE_ANISOTROPIC
    vec3 accum[6]=vec3[](vec3(0.0),vec3(0.0),vec3(0.0),vec3(0.0),vec3(0.0),vec3(0.0));
    const vec3 accum_dirs[6]=vec3[](vec3(1.0,0.0,0.0),vec3(-1.0,0.0,0.0),vec3(0.0,1.0,0.0),vec3(0.0,-1.0,0.0),vec3(0.0,0.0,1.0),vec3(0.0,0.0,-1.0));
#else
    vec3 accum = vec3(0);
#endif

    for(uint i=0;i<params.light_count;i++) {

        float attenuation;
        vec3 light_pos;

        if (!compute_light_vector(i,cell_index,pos,attenuation,light_pos)) {
            continue;
        }

        vec3 light_dir = pos - light_pos;
        float distance = length(light_dir);

        light_dir=normalize(light_dir);

        distance += distance_adv - mod(distance, distance_adv); //make it reach the center of the box always

        vec3 from = pos - light_dir * distance; //approximate

        if (normal.w < 0.5 && dot(normal.xyz,light_dir)>=0) {
            continue; //not facing the light
        }

        uint result = raymarch(distance,distance_adv,from,lights.data[light].direction);

        if (result != cell_index) {
            continue; //was occluded
        }

        vec3 light = lights.data[i].color * albedo.rgb * attenuation;

#ifdef MODE_ANISOTROPIC
        for(uint j=0;j<6;j++) {
            accum[j]+=max(0.0,dot(accum_dir,-light_dir))*light+emission;
        }
#else
        if (normal.w < 0.5) {
            accum+=max(0.0,dot(normal.xyz,-light_dir))*light+emission;
        } else {
            //all directions
            accum+=light+emission;
        }
#endif

    }

#ifdef MODE_ANISOTROPIC

    vec3 accum_total = accum[0]+accum[1]+accum[2]+accum[3]+accum[4]+accum[5];
    float accum_total_energy = max(dot(accum_total,GREY_VEC),0.00001);
    vec3 iso_positive = vec3(dot(aniso[0],GREY_VEC),dot(aniso[2],GREY_VEC),dot(aniso[4],GREY_VEC))/vec3(accum_total_energy);
    vec3 iso_negative = vec3(dot(aniso[1],GREY_VEC),dot(aniso[3],GREY_VEC),dot(aniso[5],GREY_VEC))/vec3(accum_total_energy);

    //store in 3D textures, total color, and isotropic magnitudes
#else
    //store in 3D texture pos, accum
#endif

}