#version 330 core

in vec3 frag_pos;
in vec3 frag_normal;
in vec2 frag_uv;

out vec4 color;

uniform sampler2D sampler;

const uint NUM_LIGHTS = 32u;

layout (std140) uniform lights
{
	uint max_p_lights;
	uint active_p_lights;
	uint max_d_lights;
	uint active_d_lights;
	uint padding;

	vec4 ambient_color;

	vec4 pl_positions[NUM_LIGHTS];
	vec4 pl_colors[NUM_LIGHTS];
	uint pl_intensities[NUM_LIGHTS]; // NOTE: 16 bytes * NUM_LIGHTS

	vec4 dl_directions[NUM_LIGHTS];
	vec4 dl_colors[NUM_LIGHTS];
	uint dl_intensities[NUM_LIGHTS]; // NOTE: 16 bytes * NUM_LIGHTS
};

const float CONSTANT_ATTENUATION = 0.1;
const float LINEAR_ATTENUATION = 0.2;
const float QUADRATIC_ATTENUATION = 0.02;


void main()
{
	vec4 diffuse_color = vec4(0);

	// NOTE: directional lights
	for (uint i = 0u; i < active_d_lights; i++) {
		vec4 light_direction = normalize(dl_directions[i]);
		float diffuse_factor =
			clamp(dot(vec4(frag_normal, 1), light_direction), 0, 1);
		diffuse_color = diffuse_color +
			dl_intensities[i] * diffuse_factor * dl_colors[i];
	}

	// NOTE: point lights
	for (uint i = 0u; i < active_p_lights; i ++) {
		vec3 direction = vec3(pl_positions[i]).xyz - frag_pos;
		float distance = length(direction);
		direction = direction / distance;

		float attenuation = CONSTANT_ATTENUATION +
							LINEAR_ATTENUATION * distance +
							QUADRATIC_ATTENUATION * pow(distance, 2);
		float diffuse_factor = clamp(dot(frag_normal, direction), 0, 1);
		vec4 added_color = pl_colors[i] * pl_intensities[i]
						* diffuse_factor / attenuation;

		diffuse_color = diffuse_color + added_color;
	}

	color = (ambient_color + diffuse_color) * texture(sampler, frag_uv.st);
}