#version 330 core

layout (location = 0) in vec3 in_quad;

layout (std140) uniform Matrices {
	mat4 proj;
	mat4 view;
};

// world chunk position
const int CHUNK_SIZE = 16;
uniform ivec3 chunk_position;

const int MAX_FACES = CHUNK_SIZE * CHUNK_SIZE * CHUNK_SIZE;
layout (std140) uniform Face {
	// normaly a uint but std140 layout
	// requires 16-byte alignment
	uvec4 face_data[MAX_FACES / 4];
};

flat out uvec2 pass_data;
out float pass_ao;

const mat3 ROT90 = mat3(
	0.0,  0.0, 1.0,
	0.0,  1.0, 0.0,
	-1.0, 0.0, 0.0
);

uint get_half(int index)
{
	int arr_index = index / 4;
	int vec_index = index % 4;
	return face_data[arr_index][vec_index];
}

uvec2 get_data(int index)
{
	uint lower = get_half(index * 2);
	uint upper = get_half(index * 2 + 1);
	return uvec2(lower, upper);
}

bool get_ao_rotate(uint data)
{
	vec4 ao;

	ao.x = (data >> 0) & 3u;
	ao.y = (data >> 2) & 3u;
	ao.z = (data >> 4) & 3u;
	ao.w = (data >> 6) & 3u;

	float a = abs(ao.x - ao.w);
	float b = abs(ao.y - ao.z);

	return a > b;
}

float get_ao(uint data, uint face)
{
	vec4 ao;

	ao.x = (data >> 0) & 3u;
	ao.y = (data >> 2) & 3u;
	ao.z = (data >> 4) & 3u;
	ao.w = (data >> 6) & 3u;

	switch (face) {
		case 0u: // PX
		case 2u: // PY
		case 4u: // PZ
			ao = ao.xywz;
			if (get_ao_rotate(data))
				ao = ao.wxyz;
			break;
		case 1u: // NX
		case 3u: // NY
		case 5u: // NZ
			if (get_ao_rotate(data))
				ao = ao.ywxz;
			ao = ao.wzxy;
			break;
	}

	return ao[gl_VertexID];
}

vec3 rotate(vec3 v, uint face)
{
	switch(face) {
		case 0u: // PX
		case 1u: // NX
			v = vec3(v.x, v.z, -v.y + 1);
			break;
		case 2u: // PY
		case 3u: // NY
			v = vec3(-v.z + 1, v.y, v.x);
			break;
		case 4u: // PZ
		case 5u: // NZ
			v = vec3(v.y, -v.x + 1, v.z);
			break;
	}

	return v;
}

vec3 get_quad(uint face, uint width, uint height)
{
	vec3 quad = in_quad;
	quad.x *= width;
	quad.y *= height;

	switch(face) {
		case 0u: // PX
			quad = quad.yzx + vec3(1, 0, 0);
			break;
		case 1u: // NX
			quad = quad.yxz;
			break;
		case 2u: // PY
			quad = quad.xyz + vec3(0, 1, 0);
			break;
		case 3u: // NY
			quad = quad.zyx;
			break;
		case 4u: // PZ
			quad = quad.zxy + vec3(0, 0, 1);
			break;
		case 5u: // NZ
			quad = quad.xzy;
			break;
	}

	return quad;
}

void main(void)
{
	// get face data
	uvec2 data = get_data(gl_InstanceID);
	uint x = (data.x >> 0) & 31u;
	uint y = (data.x >> 5) & 31u;
	uint z = (data.x >> 10) & 31u;
	uint width = (data.x >> 15) & 31u;
	uint height = (data.x >> 20) & 31u;
	uint face = (data.x >> 25) & 7u;

	// get quad verts
	vec3 quad = get_quad(face, width, height);
	if (get_ao_rotate(data.y))
		quad = rotate(quad, face);

	// get position
	vec3 position = vec3(x, y, z);
	position += chunk_position * CHUNK_SIZE;
	position += quad;

	// draw
	gl_Position = proj * view * vec4(position, 1.0);

	// fragment input
	pass_data = data;
	pass_ao = get_ao(data.y, face);
}