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use number_traits::{Cast, Num};

use cubic::cubic;
use linear::linear;
use quadratic::quadratic;

#[inline]
pub fn n<'a, T, F>(points: &'a [T], t: F) -> T
where
    T: Copy + Num + Cast<F>,
    F: Copy + Num + Cast<T>,
{
    if t <= F::zero() {
        match points.len() {
            0 => T::zero(),
            _ => points[0],
        }
    } else if t >= F::one() {
        match points.len() {
            0 => T::zero(),
            n => points[n - 1],
        }
    } else {
        match points.len() {
            0 => T::zero(),
            1 => points[0],
            2 => linear(points[0], points[1], t),
            3 => cubic(points[0], points[1], points[2], t),
            4 => quadratic(points[0], points[1], points[2], points[3], t),
            n => casteljau(points, n - 1, 0, t),
        }
    }
}

#[inline]
fn casteljau<'a, T, F>(points: &'a [T], i: usize, j: usize, t: F) -> T
where
    T: Copy + Num + Cast<F>,
    F: Copy + Num + Cast<T>,
{
    if i == 0_usize {
        points[j]
    } else {
        let p0 = casteljau(points, i - 1, j, t);
        let p1 = casteljau(points, i - 1, j + 1, t);

        let x0 = p0.cast();
        let x1 = p1.cast();

        ((F::one() - t) * x0 + t * x1).cast()
    }
}

#[test]
fn test_n() {
    assert_eq!(n::<isize, f32>(&[], 0.0), 0);
    assert_eq!(n::<isize, f32>(&[], 0.5), 0);
    assert_eq!(n::<isize, f32>(&[], 1.0), 0);

    assert_eq!(n(&[0, 150, 200, 0], 0.25), 91);
    assert_eq!(n(&[0, 150, 200, 0], 0.5), 131);
    assert_eq!(n(&[0, 150, 200, 0], 0.75), 105);

    assert_eq!(n(&[0, 150, 200, 50, 0], 0.25), 106);
    assert_eq!(n(&[0, 150, 200, 50, 0], 0.5), 124);
    assert_eq!(n(&[0, 150, 200, 50, 0], 0.75), 69);
}