use crate::number::Number;
use crate::poly::Poly;

pub enum Lerp {
    Node(Box<Lerp>, Box<Lerp>),
    Leaf(Number, Number),
}

impl Lerp {
    pub fn new(v: Vec<Number>) -> Box<Lerp> {
        Lerp::new_s(&v[..])
    }

    fn new_s(v: &[Number]) -> Box<Lerp> {
        match v.len() {
            0 => Box::new(Lerp::Leaf(0.0, 0.0)),
            1 => Box::new(Lerp::Leaf(v[0], v[0])),
            2 => Box::new(Lerp::Leaf(v[0], v[1])),
            _ => Box::new(Lerp::Node(
                Lerp::new_s(&v[0..v.len() - 1]),
                Lerp::new_s(&v[1..v.len()]),
            )),
        }
    }
}

pub fn lp(l: Box<Lerp>) -> Poly {
    match *l {
        Lerp::Leaf(a, b) => Poly::new(vec![a, b - a]),
        Lerp::Node(a, b) => {
            let a = lp(a);
            let b = lp(b);
            let c = &b - &a;
            &a + &(&c * &Poly::new(vec![0.0, 1.0]))
        }
    }
}