#version 430 core
#define PI 3.14159265359

float AMBIENT = 0.1;

uniform vec3 albedo;
uniform float metallic;
uniform float roughness;
uniform vec3 color;
uniform vec3 lightPos;
uniform vec3 viewPos;
uniform vec3 ambientColor;
uniform sampler2D colorTexture;

in vec3 fragNormal;
in vec3 fragPosition;
in vec2 texCoords;

out vec4 outColor;

float specularD(float NdotH, float roughness)
{
    float alpha = roughness * roughness;
    float alpha2 = alpha * alpha;
    float cos2ThetaH = NdotH * NdotH;

    float expTerm = (cos2ThetaH - 1.0) / (alpha2 * cos2ThetaH);
    return exp(expTerm) / (PI * alpha2 * pow(cos2ThetaH + alpha2 - 1.0, 2.0));
}

vec3 specularF(float LdotH, vec3 F0)
{
    return F0 + (vec3(1.0) - F0) * pow(1.0 - LdotH, 5.0);
}

float specularG(float NdotL, float NdotV, float roughness)
{
    float k = (roughness + 1.0) * (roughness + 1.0) / 8.0;

    float GL = NdotL / (NdotL * (1.0 - k) + k);
    float GV = NdotV / (NdotV * (1.0 - k) + k);

    return GL * GV;
}

void main()
{
    vec3 normal = normalize(fragNormal);
    vec3 viewDir = normalize(viewPos - fragPosition);
    vec3 lightDir = normalize(lightPos - fragPosition);

    vec3 F0 = vec3(0.04); 
    F0 = mix(F0, albedo, metallic);

    float NdotL = max(dot(normal, lightDir), 0.0);
    float NdotV = max(dot(normal, viewDir), 0.0);

    vec3 H = normalize(lightDir + viewDir);
    float NdotH = max(dot(normal, H), 0.0);
    float LdotH = max(dot(lightDir, H), 0.0);
    vec3 albedo = texture(colorTexture, texCoords).rgb;
    albedo *= 2.0;
    vec3 specular = F0 * (specularD(NdotH, roughness) * specularF(LdotH, F0) * specularG(NdotL, NdotV, roughness)) / (4.0 * NdotL * NdotV);

    vec3 diffuse = (1.0 - F0) * albedo / PI;

    vec3 ambient = ambientColor * AMBIENT;

    vec3 finalColor = ambient + (diffuse + specular) * NdotL;

    outColor = vec4(finalColor, 1.0);
}