#include <array>
#include <cmath>
#include "light/light.h"
#include "scene/scene.h"
#include "shader/brdfshader.h"

BrdfShader::BrdfShader(char const *fileName, Color const &scale)
        : scale(scale), brdf(std::make_unique<BRDFRead>(fileName)) {}

Color BrdfShader::shade(Scene const &scene, Ray const &ray) const {
    // Calculate theta and phi
    float thetaIn = std::acos(dotProduct(-ray.normal, ray.direction));
    float phiIn = 0.0f;

    // Derive local coordinate system
    Vector3d const x = crossProduct(-ray.direction, ray.normal);
    Vector3d const y = crossProduct(ray.normal, x);

    // Accumulate the light over all light sources
    Color illuminationColor;
    for (const auto &light : scene.lights()) {
        Light::Illumination illum;
        illum = light->illuminate(scene, ray);

        // Diffuse term
        float const cosine = dotProduct(-illum.direction, ray.normal);
        if (cosine > 0) {
            Color color;

            // Avoid numeric instability
            if (cosine < 1) {
                float const thetaOut = std::acos(cosine);

                // Project outgoing vector into local coordinate system
                Vector3d const c = crossProduct(-illum.direction, ray.normal);
                float const phiOut = std::atan2(dotProduct(c, y), dotProduct(c, x));

                color = Color(brdf->lookupBrdfValues(thetaIn, phiIn, thetaOut, phiOut));
            } else {
                color = Color(brdf->lookupBrdfValues(thetaIn, phiIn, 0, 0));
            }

            // Calculate colors
            Color const diffuseColor = scale * color * cosine;
            illuminationColor += diffuseColor * illum.color;
        }
    }
    return illuminationColor;
}