Shift.swift

enum ShiftDirection {
    case Left, Right
}

func shiftBy<T>(shiftDegree: Int, inArray: [T], shiftDirection: ShiftDirection) -> [T] {
    guard inArray.count > 2 else {
        return inArray
    }

    let safeShift = (shiftDegree + (shiftDirection == .Right ? (inArray.count - 2) : 0)) % inArray.count
    let length: Int = inArray.count
    var shiftedArray = [T]()

    for pos in 0..<length {
        let posNext = (pos + safeShift) % length
        shiftedArray += [inArray[posNext]]
    }

    return shiftedArray
}

func shiftAndCenter<T>(offset: Int, inArray: [T]) -> [T] {

    let safeOffset = offset % inArray.count
    let middle = (inArray.count / 2) + (inArray.count % 2)
    let shiftDegree = (safeOffset + middle) % (inArray.count )
    return shiftBy(shiftDegree, inArray: inArray, shiftDirection: .Right)
}