uniform int u_num_lights;

struct light_t {
    int type;
    vec3 diffuse;
    vec3 specular;
    vec3 ambient;
    vec3 pos;
    vec3 dir;
    float power;
    float radius;
    float innerCone;
    float outerCone;

    // falloff
    float constant;
    float linear;
    float quadratic;
};

#define MAX_LIGHTS 16
const int LIGHT_DIRECTIONAL = 0;
const int LIGHT_POINT = 1;
const int LIGHT_SPOT = 2;

uniform light_t u_lights[MAX_LIGHTS];

#ifdef SHADING_PHONG
vec3 shading_phong(light_t l) {
    vec3 lightDir;
    float attenuation = 1.0;

    if (l.type == LIGHT_DIRECTIONAL) {
        lightDir = normalize(-l.dir);
    } else if (l.type == LIGHT_POINT || l.type == LIGHT_SPOT) {
        vec3 toLight = l.pos - v_position_ws;
        lightDir = normalize(toLight);
        float distance = length(toLight);
        
        /* fast-reject based on radius */
        if (l.radius != 0.0 && distance > l.radius) {
            return vec3(0,0,0);
        }
        attenuation = 1.0 / (l.constant + l.linear * distance + l.quadratic * (distance * distance));

        if (l.type == LIGHT_SPOT) {
            float angle = dot(l.dir, -lightDir);
            if (angle > l.outerCone) {
                float intensity = (angle-l.outerCone)/(l.innerCone-l.outerCone);
                attenuation *= clamp(intensity, 0.0, 1.0);
            } else {
                attenuation = 0.0;
            }
        }
    }

    // fast-rejection for faraway vertices
    if (attenuation <= 0.01) {
        return vec3(0,0,0);
    }

    vec3 n = normalize(v_normal_ws);

    float diffuse = max(dot(n, lightDir), 0.0);

    vec3 halfVec = normalize(lightDir + u_cam_dir);
    float specular = pow(max(dot(n, halfVec), 0.0), l.power);

    return (attenuation*l.ambient + diffuse*attenuation*l.diffuse + specular*attenuation*l.specular);
}
#endif
#ifdef SHADING_VERTEXLIT
vec3 shading_vertexlit(light_t l) {
    vec3 lightDir;
    float attenuation = 1.0;

    if (l.type == LIGHT_DIRECTIONAL) {
        lightDir = normalize(-l.dir);
    } else if (l.type == LIGHT_POINT || l.type == LIGHT_SPOT) {
        vec3 toLight = l.pos - v_position_ws;
        lightDir = normalize(toLight);
        float distance = length(toLight);
        
        /* fast-reject based on radius */
        if (l.radius != 0.0 && distance > l.radius) {
            return vec3(0,0,0);
        }
        attenuation = 1.0 / (l.constant + l.linear * distance + l.quadratic * (distance * distance));

        if (l.type == LIGHT_SPOT) {
            float angle = dot(l.dir, -lightDir);
            if (angle > l.outerCone) {
                float intensity = (angle-l.outerCone)/(l.innerCone-l.outerCone);
                attenuation *= clamp(intensity, 0.0, 1.0);
            } else {
                attenuation = 0.0;
            }
        }
    }

    // fast-rejection for faraway vertices
    if (attenuation <= 0.01) {
        return vec3(0,0,0);
    }

    vec3 n = normalize(v_normal_ws);

    float diffuse = max(dot(n, lightDir), 0.0);

    vec3 halfVec = normalize(lightDir + u_cam_dir);
    float specular = pow(max(dot(n, halfVec), 0.0), l.power);

    return (attenuation*l.ambient + diffuse*attenuation*l.diffuse + specular*attenuation*l.specular);
}

#endif

vec3 lighting() {
    vec3 lit = vec3(0,0,0);
#ifndef SHADING_NONE
    #ifdef SHADING_PHONG
        for (int i=0; i<u_num_lights; i++) {
            lit += shading_phong(u_lights[i]);
        }
    #endif
    #ifdef SHADING_VERTEXLIT
        for (int i=0; i<u_num_lights; i++) {
            lit += shading_vertexlit(u_lights[i]);
        }
    #endif
    #ifdef SHADING_PBR
    #endif
#endif
    return lit;
}