/**
 *
 * RenderPipeline
 *
 * Copyright (c) 2014-2016 tobspr <tobias.springer1@gmail.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 */

#pragma once

#pragma include "includes/material.inc.glsl"
#pragma include "includes/brdf.inc.glsl"
#pragma include "includes/ies_lighting.inc.glsl"

// Computes the quadratic attenuation curve
float attenuation_curve(float dist_square, float radius) {
    #if 0
        return step(dist_square, radius * radius);
    #endif

    #if 1
        float factor = dist_square / (radius * radius);
        float smooth_factor = saturate(1.0 - factor * factor);
        return smooth_factor * smooth_factor / max(0.01 * 0.01, dist_square);
    #endif
}


// Computes the attenuation for a spot light
float get_spotlight_attenuation(vec3 l, vec3 light_dir, float fov, float radius,
        float dist_sq, int ies_profile) {
    float dist_attenuation = attenuation_curve(dist_sq, radius);
    float cos_angle = dot(l, -light_dir);

    // Rescale angle to fit the full range of the IES profile. We only do this
    // for spot lights, for point lights we use the actual angle.
    // This is NOT physically correct for spotlights without a FoV of 180deg.
    // However, IES profiles might look quite boring when not getting rescaled,
    // so the rescaling is performed. 
    float linear_angle = (cos_angle - fov) / (1 - fov);
    float angle_att = saturate(linear_angle);
    float ies_factor = get_ies_factor(ies_profile, linear_angle, 0);
    return ies_factor * angle_att * angle_att * dist_attenuation;
}


// Closest point on spherical area light, also returns energy factor
vec3 get_spherical_area_light_vector(vec3 n, vec3 l_unscaled, vec3 v, float radius) {
    vec3 r = reflect(-v, n);
    vec3 center_to_ray = dot(l_unscaled, r) * r - l_unscaled;
    vec3 closest_point = l_unscaled + center_to_ray *
        saturate(radius / max(1e-3, length(center_to_ray)));
    return closest_point;
}

vec3 get_spherical_area_light_horizon(vec3 l_unscaled, vec3 n, float radius) {
    return normalize(l_unscaled + n * (0.5 * radius));
}

float get_spherical_area_light_energy(float alpha, float radius, float dist_sq) {
     return max(0.000005, alpha * alpha) / max(0.01, radius * radius) * 4 * M_PI;
}

// Computes a lights influence
// TODO: Make this method faster
vec3 apply_light(Material m, vec3 v, vec3 l, vec3 light_color, float attenuation, float shadow,
    vec3 transmittance, float energy, float clearcoat_energy, vec3 l_diffuse) {

    // Debugging: Fast rendering path
    #if 0
        return light_color * attenuation;
    #endif

    float NxL = saturate(dot(m.normal, l_diffuse));

    if (m.shading_model == SHADING_MODEL_FOLIAGE) {
        transmittance = transmittance.xxx;
    } else if (m.shading_model == SHADING_MODEL_SKIN) {
        NxL = saturate(0.3 + dot(m.normal, l_diffuse));
    } else {
        transmittance = vec3(1);
    }

    // Compute the dot products
    vec3 h = normalize(l + v);
    float NxV = max(1e-5, dot(m.normal, v));
    float NxH = max(1e-5, dot(m.normal, h));
    float VxH = clamp(dot(v, h), 1e-5, 1.0);
    float LxH = max(0, dot(l, h));

    vec3 f0 = get_material_f0(m);

    // Diffuse contribution
    vec3 shading_result = brdf_diffuse(NxV, NxL, LxH, VxH, m.roughness)
                            * m.basecolor * (1 - m.metallic);

    // Specular contribution:
    // We add some roughness for clearcoat - this is due to the reason that
    // light gets scattered and thus a wider highlight is shown.
    // This approximates the reference in mitsuba very well.
    // float distribution = brdf_distribution(NxH, m.roughness);
    float distribution = brdf_distribution(NxH, m.roughness); // xxx
    float visibility = brdf_visibility(NxL, NxV, NxH, VxH, m.roughness);
    vec3 fresnel = brdf_schlick_fresnel(f0, LxH);


    // The division by 4 * NxV * NxL is done in the geometric (visibility) term
    // already, so to evaluate the complete brdf we just do a multiply
    shading_result += (distribution * visibility) * fresnel / (4.0 * NxV * NxL) * energy;

    if (m.shading_model == SHADING_MODEL_CLEARCOAT) {
        float distribution_coat = brdf_distribution(NxH, CLEARCOAT_ROUGHNESS);
        float visibility_coat = brdf_visibility(NxL, NxV, NxH, VxH, CLEARCOAT_ROUGHNESS);
        vec3 fresnel_coat = brdf_schlick_fresnel(vec3(CLEARCOAT_SPECULAR), LxH);

        // Approximation to match reference
        shading_result *= (1 - fresnel_coat.x);
        shading_result *= 0.4 + 3.0 * m.linear_roughness;
        shading_result *= 0.5 + 0.5 * m.basecolor;

        vec3 coat_spec = (distribution_coat * visibility_coat * clearcoat_energy) * fresnel_coat;
        shading_result += coat_spec;
    }

    return max(vec3(0),
        (shading_result * light_color) * (attenuation * shadow * NxL) * transmittance);
}

vec3 apply_light(Material m, vec3 v, vec3 l, vec3 light_color, float attenuation,
        float shadow, vec3 transmittance) {
    return apply_light(
        m, v, l, light_color, attenuation, shadow, transmittance, 1.0, 1.0, l);
}