#version 460

layout(local_size_x = 4, local_size_y = 4, local_size_z = 4) in;

const int CHUNK_SIZE = 16;
const int CHUNK_AREA = CHUNK_SIZE * CHUNK_SIZE;
const int VOXEL_COUNT = CHUNK_SIZE * CHUNK_SIZE * CHUNK_SIZE;

const uint VERTICES_PER_FACE = 6u;
const uint MAX_VISIBLE_FACES_PER_CHUNK = uint(CHUNK_SIZE * CHUNK_SIZE * CHUNK_SIZE * 6);

layout(std430, binding = 0) readonly buffer VoxelData {
    uint voxels[];
};

layout(std430, binding = 1) buffer FaceBuffer {
    uint faces[];
};

struct DrawCommand {
    uint vertexCount;
    uint instanceCount;
    uint firstVertex;
    uint firstInstance;
};

layout(std430, binding = 2) buffer DrawCommands {
    DrawCommand drawCmds[];
};

layout(std430, binding = 3) buffer Counters {
    uint faceCount;
} counters;

layout(push_constant) uniform ChunkInfo {
    ivec3 chunkPos;
    int slot;
    uint faceOffset;
    uint unused0;
    uint indirectCommandIndex;
    uint padding0;
};

uint flatten(ivec3 pos) {
    return uint((pos.x * CHUNK_AREA) + (pos.y * CHUNK_SIZE) + pos.z);
}

uint getVoxel(ivec3 pos) {
    if (pos.x < 0 || pos.x >= CHUNK_SIZE) return 0u;
    if (pos.y < 0 || pos.y >= CHUNK_SIZE) return 0u;
    if (pos.z < 0 || pos.z >= CHUNK_SIZE) return 0u;

    return voxels[flatten(pos)];
}
uint hash21(uvec2 p) {
    p = p * 1664525u + 1013904223u;
    p.x += p.y * 1664525u;
    p.y += p.x * 1664525u;
    return p.x ^ (p.x >> 16);
}

uint random_1_to_3(vec2 uv, uint customSeed) {
    uvec2 p = uvec2(floatBitsToUint(uv.x), floatBitsToUint(uv.y));
    p.x ^= customSeed;
    uint randInt = hash21(p);
    return (randInt % 3u) + 1u;
}

uint packFace(uvec3 voxelPos, uint faceIndex, uint materialId) {
    uint randomFaceValue = random_1_to_3(vec2(voxelPos.x, voxelPos.z),faceOffset);
    uint textureIndexX = 0u;
    uint textureIndexY = 0u;
    if(materialId == 1u){
        if(faceIndex == 0u){
            textureIndexX = 0u;
            textureIndexY = randomFaceValue;
        } else if(faceIndex == 1u){
            textureIndexX = 1u;
            textureIndexY = 0u;
        }
        else{
            textureIndexX = 0u;
            textureIndexY = 0u;
        }
    } else if(materialId == 2u){
        textureIndexX = 1u;
        textureIndexY = 0u;
    }else if(materialId == 3u){
        textureIndexX = 1u;
        textureIndexY = 0u;
    }else if(materialId == 4u){
        textureIndexX = 1u;
        textureIndexY = randomFaceValue;
    }else if(materialId == 5u){
        textureIndexX = 2u;
        textureIndexY = 3u;
    }else if(materialId == 5u){
        if (faceIndex == 0u || faceIndex == 1u){
            textureIndexX = 2u;
            textureIndexY = 1u;
        } else{
            textureIndexX = 2u;
            textureIndexY = 2u;
        }
    }else if(materialId == 6u){
        textureIndexX = 2u;
        textureIndexY = 0u;
    }

    return (voxelPos.x & 0x1Fu) |
    ((voxelPos.y & 0x1Fu) << 5u) |
    ((voxelPos.z & 0x1Fu) << 10u) |
    ((faceIndex & 0x7u) << 15u) |
    ((materialId & 0xFFu) << 18u) |
    ((textureIndexX & 0x7u) << 26u) |
    ((textureIndexY & 0x7u) << 29u);
}

void emitFace(ivec3 voxelPos, uint faceIndex, uint voxelType) {
    uint localFace = atomicAdd(counters.faceCount, 1u);

    if (localFace >= MAX_VISIBLE_FACES_PER_CHUNK) {
        return;
    }

    faces[faceOffset + localFace] = packFace(uvec3(voxelPos), faceIndex, voxelType);

    atomicAdd(drawCmds[indirectCommandIndex].vertexCount, VERTICES_PER_FACE);
}

void main() {
    ivec3 pos = ivec3(gl_GlobalInvocationID.xyz);

    if (pos.x >= CHUNK_SIZE || pos.y >= CHUNK_SIZE || pos.z >= CHUNK_SIZE) {
        return;
    }

    uint current = getVoxel(pos);

    if (current == 0u) {
        return;
    }

    if (current == 4u) {
        emitFace(pos, 6u, current);
        emitFace(pos, 7u, current);
        return;
    }

    if (getVoxel(pos + ivec3( 0,  1,  0)) == 0u || getVoxel(pos + ivec3( 0,  1,  0)) == 4u) emitFace(pos, 0u, current);
    if (getVoxel(pos + ivec3( 0, -1,  0)) == 0u || getVoxel(pos + ivec3( 0, -1,  0)) == 4u) emitFace(pos, 1u, current);
    if (getVoxel(pos + ivec3( 1,  0,  0)) == 0u || getVoxel(pos + ivec3( 1,  0,  0)) == 4u) emitFace(pos, 2u, current);
    if (getVoxel(pos + ivec3(-1,  0,  0)) == 0u || getVoxel(pos + ivec3( -1,  0,  0)) == 4u) emitFace(pos, 3u, current);
    if (getVoxel(pos + ivec3( 0,  0,  1)) == 0u|| getVoxel(pos + ivec3( 0,  0, 1)) == 4u) emitFace(pos, 4u, current);
    if (getVoxel(pos + ivec3( 0,  0, -1)) == 0u || getVoxel(pos + ivec3( 0,  0, -1)) == 4u) emitFace(pos, 5u, current);
}