use crate::hittable;
use crate::types_defined::{HitRecord, Point, Ray, Sphere};

impl Sphere {
    pub fn new(c: Point, r: f32) -> Self {
        Self {
            center: c,
            radius: r,
        }
    }
}

impl hittable::Hittable for Sphere {
    fn hit(&self, r: &Ray, t_min: f32, t_max: f32) -> HitRecord {
        let a: f32 = r.direction.length_squared();
        let h = r.direction.dot(self.center - r.point);
        // let b = -2.0 * r.direction.dot(sphere_center - r.point);
        let c = (self.center - r.point).length_squared() - self.radius * self.radius;

        let discriminant = h * h - a * c;

        // // 两个交点
        let disc_sqrt = discriminant.sqrt();
        let near = (h - disc_sqrt) / a;
        let far = (h + disc_sqrt) / a;

        let mut root = near;
        if root <= t_min || root >= t_max {
            root = far;
            if root <= t_min || root >= t_max {
                root = -1.0;
            }
        }

        let p = r.at(root);
        let normal = (p - self.center) / self.radius;
        HitRecord {
            t: root,
            // p,
            normal,
            // check if r.p inside(>=0) the sphere.
            front_face: r.direction.dot(normal) < 0.0,
        }
    }
}