#version 330 core

out vec4 FragColor;

in vec2 TexCoords;

uniform sampler2D gPosition;
uniform sampler2D gNormal;
uniform sampler2D gAlbedoSpec;

struct Light {
    vec3 Position;
    vec3 Color;

    float Linear;
    float Quadratic;
};

const int NR_LIGHTS = 32;
uniform Light lights[NR_LIGHTS];
uniform vec3 viewPos;

void main()
{
    // retrieve data from gbuffer
    vec3 FragPos = texture(gPosition, TexCoords).rgb;
    vec3 Normal = texture(gNormal, TexCoords).rgb;
    // vec3 Diffuse = texture(gAlbedoSpec, TexCoords).rgb;
    // float Specular = texture(gAlbedoSpec, TexCoords).a;

    // then calculate lighting as usual
    vec3 lighting  = Diffuse * 0.1; // hard-coded ambient component
    vec3 viewDir  = normalize(viewPos - FragPos);
    for(int i = 0; i < NR_LIGHTS; ++i)
    {
	// diffuse
	vec3 lightDir = normalize(lights[i].Position - FragPos);
	vec3 diffuse = max(dot(Normal, lightDir), 0.0) * Diffuse * lights[i].Color;
	// specular
	vec3 halfwayDir = normalize(lightDir + viewDir);
	float spec = pow(max(dot(Normal, halfwayDir), 0.0), 16.0);
	vec3 specular = lights[i].Color * spec * Specular;
	// attenuation
	float distance = length(lights[i].Position - FragPos);
	float attenuation = 1.0 / (1.0 + lights[i].Linear * distance + lights[i].Quadratic * distance * distance);
	diffuse *= attenuation;
	specular *= attenuation;
	lighting += diffuse + specular;
    }
    FragColor = vec4(lighting, 1.0);
}