#include "vec3.h"

Vec3 random_in_unit_sphere() {
    while (true) {
        auto p = Vec3::random(-1, 1);
        if (p.length_squared() >= 1) continue;
        return p;
    }
}

Vec3 random_unit_vector() {
    auto a = random_double(0, 2*pi);
    auto z = random_double(-1, 1);
    auto r = std::sqrt(1 - z*z);
    return Vec3(r*std::cos(a), r*std::sin(a), z);
}

Vec3 random_in_hemisphere(const Vec3& normal) {
    Vec3 in_unit_sphere = random_in_unit_sphere();
    if (dot(in_unit_sphere, normal) > 0.0)
        return in_unit_sphere;
    else
        return -in_unit_sphere;
}

Vec3 refract(const Vec3& uv, const Vec3& n, double etai_over_etat) {
    auto cos_theta = dot(-uv, n);
    Vec3 r_out_parallel = etai_over_etat * (uv + cos_theta*n);
    Vec3 r_out_perp = - std::sqrt(1.0 - r_out_parallel.length_squared()) * n;
    return r_out_parallel + r_out_perp;
}

Vec3 random_in_unit_disk() {
    while (true) {
        auto p = Vec3(random_double(-1, 1), random_double(-1, 1), 0);
        if (p.length_squared() >= 1) continue;
        return p;
    }
}