export const fn = (p0: number, p1: number, p2: number, p3: number, t: number): number => {
    const v0: number = (p2 - p0) * 0.5
    const v1: number = (p3 - p1) * 0.5
    const t2: number = t * t
    const t3: number = t * t2

    return (2 * p1 - 2 * p2 + v0 + v1) * t3 + (-3 * p1 + 3 * p2 - 2 * v0 - v1) * t2 + v0 * t + p1
}

export const CatmullRom = (v: number[], k: number): number => {
    const m: number = v.length - 1
    let f: number = m * k
    let i: number = Math.floor(f)

    if (v[0] === v[m]) {
        if (k < 0) {
            i = Math.floor((f = m * (1 + k)))
        }

        return fn(v[(i - 1 + m) % m], v[i], v[(i + 1) % m], v[(i + 2) % m], f - i)
    } else {
        if (k < 0) {
            return v[0] - (fn(v[0], v[0], v[1], v[1], -f) - v[0])
        }

        if (k > 1) {
            return v[m] - (fn(v[m], v[m], v[m - 1], v[m - 1], f - m) - v[m])
        }

        return fn(v[i ? i - 1 : 0], v[i], v[m < i + 1 ? m : i + 1], v[m < i + 2 ? m : i + 2], f - i)
    }
}