use core::f32::math::sqrt;

use rand::RngExt;
use serde::Deserialize;

use crate::{
    objects::{hit::Hit, materials::traits::Material},
    ray::Ray,
    vec3::Colour,
};

#[derive(Debug, Deserialize)]
pub struct Dielectric {
    refraction_index: f32,
}

impl Dielectric {
    pub fn new(refraction_index: f32) -> Self {
        Self { refraction_index }
    }

    fn reflectance(cos: f32, refraction_index: f32) -> f32 {
        // Shlick's approximation
        let mut r0 = (1. - refraction_index) / (1. + refraction_index);
        r0 *= r0;
        r0 + (1. - r0) * (1. - cos).powf(5.)
    }
}

impl Material for Dielectric {
    fn scatter(&self, hit: &Hit, ray: &Ray) -> Option<(Option<Ray>, Colour)> {
        let ri = if hit.front_face() {
            1. / self.refraction_index
        } else {
            self.refraction_index
        };
        let unit = ray.dir().get_unit();
        let cos_theta = if -unit.dot(hit.n()) > 1. {
            1.
        } else {
            -unit.dot(hit.n())
        };
        let sin_theta = sqrt(1. - cos_theta * cos_theta);
        let cannot_refract = ri * sin_theta > 1.;

        let mut rng = rand::rng();
        let dir = if cannot_refract || Dielectric::reflectance(cos_theta, ri) > rng.random::<f32>()
        {
            unit.reflect(hit.n())
        } else {
            unit.refract(hit.n(), ri)
        };
        Some((Some(Ray::new(*hit.p(), dir)), Colour::new(1., 1., 1.)))
    }
}