#version 430 core
out vec4 FragColor;

// A Blinn-Phong material with textures for diffuse and specular
// lighting maps and a numeric shininess factor.
struct Material {
    sampler2D diffuse;
    sampler2D specular;    
    float shininess;
};

struct DirLight {
    vec3 direction;
    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
};

struct PointLight {
    vec3 position;
    // fall off properties
    float constant;
    float linear;
    float quadratic;

    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
};

in VS_OUT {
  vec3 FragPos;
  vec3 Normal;
  vec2 TexCoords;
  // vec4 FragPosLightSpace;
  vec4 Color;
} fs_in;

// --- Uniforms
#define NUM_POINT_LIGHTS 4
uniform vec3 viewPos;
uniform Material material;
uniform DirLight dirLight;
uniform PointLight pointLights[NUM_POINT_LIGHTS];

// --- Function prototypes
vec3 CalcDirLight(DirLight light, vec3 normal, vec3 viewDir);
vec3 CalcPointLight(PointLight light, vec3 normal, vec3 fragPos, vec3 viewDir);

void main() {
  vec3 norm = normalize(fs_in.Normal);
  vec3 viewDir = normalize(viewPos - fs_in.FragPos);

  vec3 result = CalcDirLight(dirLight, norm, viewDir);
  for (int i = 0; i < 4; i++) {
    result += CalcPointLight(pointLights[i], norm, fs_in.FragPos, viewDir);
  }

//   FragColor = vec4(result, 1.0);
  FragColor = fs_in.Color + 0.5;
}

vec3 CalcDirLight(DirLight light, vec3 normal, vec3 viewDir)
{
    vec3 lightDir = normalize(-light.direction);
    // diffuse shading
    float diff = max(dot(normal, lightDir), 0.0);
    // specular shading
    vec3 reflectDir = reflect(-lightDir, normal);
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
    // combine result
    vec3 ambient = light.ambient * vec3(texture(material.diffuse, fs_in.TexCoords));
    vec3 diffuse = light.diffuse * diff * vec3(texture(material.diffuse, fs_in.TexCoords));
    vec3 specular = light.specular * spec * vec3(texture(material.specular, fs_in.TexCoords));
    return (ambient + diffuse + specular);
}

vec3 CalcPointLight(PointLight light, vec3 normal, vec3 fragPos, vec3 viewDir)
{
    vec3 lightDir = normalize(light.position - fragPos);
    // diffuse
    float diff = max(dot(normal, lightDir), 0.0);
    // specular
    vec3 reflectDir = reflect(-lightDir, normal);
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
    // attentuation
    float distance = length(light.position - fragPos);
    float attentuation = 1.0 / (light.constant + light.linear * distance * light.quadratic * (distance * distance));
    // result
    vec3 ambient = light.ambient * vec3(texture(material.diffuse, fs_in.TexCoords));
    vec3 diffuse = light.diffuse * diff * vec3(texture(material.diffuse, fs_in.TexCoords));
    vec3 specular = light.specular * spec * vec3(texture(material.specular, fs_in.TexCoords));
    ambient *= attentuation;
    diffuse *= attentuation;
    specular *= attentuation;
    return (ambient + diffuse + specular);
}