#ifndef MATERIAL_H
#define MATERIAL_H

#include "hittable.h"
#include "rtweekend.h"
#include "vec3.h"

struct hit_record;

class material {
	public:
		virtual bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered) const = 0;
};


class lambertian : public material {
	public:
		lambertian(const color& a) : albedo(a) {}

		bool scatter(
			const ray &r_in, const hit_record &rec, color &attenuation, ray &scattered
		) const override {
			auto scatter_direction = rec.normal + random_in_hemisphere(rec.normal);

			// Catch degenerate scatter direction
			if (scatter_direction.near_zero())
				scatter_direction = rec.normal;

			scattered = ray(rec.p, scatter_direction);
			attenuation = albedo;
			return true;
		}

	public:
		color albedo;
};

class metal : public material {
	public:
		metal(const color& a, double f) : albedo(a), fuzz(f < 1 ? f : 1) {}

		bool scatter(
				const ray &r_in, const hit_record &rec, color &attenuation, ray &scattered
		) const override {
			vec3 reflected = reflect(unit_vector(r_in.direction()), rec.normal);
			scattered = ray(rec.p, reflected + fuzz*random_in_hemisphere(rec.normal));
			attenuation = albedo;
			return (dot(scattered.direction(), rec.normal) > 0);
		}

	public:
		color albedo;
		double fuzz;
};

class dialectric : public material {
	public:
		dialectric(double index_of_refraction): ir(index_of_refraction) {}

		bool scatter(
			const ray &r_in, const hit_record &rec, color &attenuation, ray &scattered
		) const override {
			attenuation = color(1.0, 1.0, 1.0);
			double refraction_ratio = rec.front_face ? (1.0/ir) : ir;

			vec3 unit_direction = unit_vector(r_in.direction());
			double cos_theta = fmin(dot(-unit_direction, rec.normal), 1.0);
			double sin_theta = sqrt(1 - cos_theta*cos_theta);

			bool cannot_refract = refraction_ratio * sin_theta > 1.0;
			vec3 direction;
			if (cannot_refract || reflectance(cos_theta, refraction_ratio) > random_double())
				direction = reflect(unit_direction, rec.normal);
			else
				direction = refract(unit_direction, rec.normal, refraction_ratio);

			scattered = ray(rec.p, direction);
			return true;
		}


	public:
		double ir; // Index of Refraction

	private:
		static double reflectance(double cosine, double ref_idx) {
			// Use Schlick's approximation for reflectance
			auto r0 = (1-ref_idx) /(1+ref_idx);
			r0 = r0*r0;
			return r0 + (1-r0)*pow((1 - cosine), 5);
		}
};

#endif
