#version 330 core
#define NR_POINT_LIGHTS 4

struct Material {
    sampler2D diffuse;
    sampler2D specular;
    float shininess;
};

struct DirLight {
    vec3 direction;

    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
};

struct PointLight {
    vec3 position;

    float constant;
    float linear;
    float quadratic;

    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
};

struct FlashLight {
    vec3 position;
    vec3 direction;

    vec3 ambient;
    vec3 diffuse;
    vec3 specular;

    float cutOff;
    float outerCutOff;
    float constant;
    float linear;
    float quadratic;
};

in vec3 Normal;
in vec3 FragPos;
in vec2 TexCoords;

out vec4 FragColor;

uniform vec3 viewPos;
uniform Material material;
uniform DirLight dirLight;
uniform PointLight pointLight[NR_POINT_LIGHTS];
uniform FlashLight flashLight;

vec3 calcDirLight(DirLight light, vec3 normal, vec3 viewDir)
{
    vec3 lightDir = normalize(-light.direction);
    // 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);

    vec3 ambient = light.ambient * texture(material.diffuse, TexCoords).rgb;
    vec3 diffuse = light.diffuse * diff * texture(material.diffuse, TexCoords).rgb;
    vec3 specular = light.specular * spec * texture(material.specular, TexCoords).rgb;

    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);

    //attenuation
    float dist = length(light.position - fragPos);
    float attenuation = 1.0 / (light.constant + light.linear * dist + 
                        light.quadratic * (dist * dist));

    vec3 ambient = light.ambient * texture(material.diffuse, TexCoords).rgb;
    vec3 diffuse = light.diffuse * diff * texture(material.diffuse, TexCoords).rgb;
    vec3 specular = light.specular * spec * texture(material.specular, TexCoords).rgb;

    ambient *= attenuation;
    diffuse *= attenuation;
    specular *= attenuation;

    return ambient + diffuse + specular;
}

vec3 calcFlashLight(FlashLight light, vec3 normal, vec3 fragPos, vec3 viewDir)
{
    vec3 lightDir = normalize(light.position - fragPos);
    float theta = dot(lightDir, normalize(-light.direction));
    float epsilon = light.cutOff - light.outerCutOff;
    float intensity = clamp((theta - light.outerCutOff) / epsilon, 0.0, 1.0);

    // 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);

    //attenuation
    float dist = length(light.position - fragPos);
    float attenuation = 1.0 / (light.constant + light.linear * dist + 
                        light.quadratic * (dist * dist));

    vec3 ambient = light.ambient * texture(material.diffuse, TexCoords).rgb;
    vec3 diffuse = light.diffuse * diff * texture(material.diffuse, TexCoords).rgb;
    vec3 specular = light.specular * spec * texture(material.specular, TexCoords).rgb;

    diffuse *= attenuation * intensity;
    specular *= attenuation * intensity;

    return ambient + diffuse + specular;
}

void main()
{
    // properties
    vec3 norm = normalize(Normal);
    vec3 viewDir = normalize(viewPos - FragPos);

    // 1. Directional light
    vec3 result = calcDirLight(dirLight, norm, viewDir);

    // 2. Point lights
    for (int i = 0; i < NR_POINT_LIGHTS; i++)
        result += calcPointLight(pointLight[i], norm, FragPos, viewDir);

    // 3. Spot light
    result += calcFlashLight(flashLight, norm, FragPos, viewDir);

    FragColor = vec4(result, 1.0);
}