use crate::types_defined::{Ray, Vec3};

pub fn clamp(value: f32, low: f32, high: f32) -> f32 {
    if value < low {
        return low;
    }
    if value > high {
        return high;
    }
    return value;
}

pub fn near_zero(v: Vec3) -> bool {
    const EPSILON: f32 = 1e-4;

    v.x.abs() < EPSILON && v.y.abs() < EPSILON && v.z.abs() < EPSILON
}

pub fn reflect(v: Vec3, n: Vec3) -> Vec3 {
    v - ((2.0 * v.dot(n)) * n)
}

// v, normal, 折射率
pub fn refract(uv: Vec3, n: Vec3, etai_over_etat: f32) -> Vec3 {
    // auto cos_theta = std::fmin(dot(-uv, n), 1.0);
    // vec3 r_out_perp =  etai_over_etat * (uv + cos_theta*n);
    // vec3 r_out_parallel = -std::sqrt(std::fabs(1.0 - r_out_perp.length_squared())) * n;
    // return r_out_perp + r_out_parallel;
    let cos_theta = (-uv.dot(n)).min(1.0);
    let r_out_perp = etai_over_etat * (uv + cos_theta * n);
    let r_out_parallel = -(f32::sqrt(f32::abs(1.0 - r_out_perp.length()))) * n;
    r_out_perp + r_out_parallel

    // let v_normalized = v;
    // let n_normalized = n.normalize();

    // let cos_theta = f32::min(-v_normalized.dot(n_normalized), 1.0);
    // let sin_theta = (1.0 - cos_theta * cos_theta).sqrt();
    // // 检查是否全内反射（无法折射）
    // if etai_over_etat * sin_theta > 1.0 {
    //     return reflect(v_normalized, n)
    // }

    // let r_out_perp = etai_over_etat * (v_normalized + cos_theta * n_normalized);
    // let discriminant = 1.0 - r_out_perp.length_squared();
    // // if discriminant < 0.0 {
    // //     return -1.0 * v; // 全内反射，返回零向量（或改为反射）
    // // }
    // let r_out_parallel = -discriminant * n_normalized;
    
    // r_out_perp + r_out_parallel
}

pub fn is_front_face(r: &Ray, outward_normal: Vec3) -> bool {
    r.direction.dot(outward_normal) < 0.0
}

pub fn front_face_normal(r: &Ray, outward_normal: Vec3) -> Vec3 {
    if is_front_face(r, outward_normal) {
        outward_normal
    } else {
        -1. * outward_normal
    }
}