package board

type shuffleDirection int

const (
	forwards shuffleDirection = iota
	backwards
)

// moveAndShuffle creates a new list where the element specified at the index of the current
// position is moved to the index of the target position. Elements within the range of the
// old and new positions will then shuffle forwards or backwards in the list depending on the
// direction of the move.
// This is currently used to move specified columns forwards or backwards on the Kanban board.
// When a column changes position the other columns shuffle forward or backwards as required.
func moveAndShuffle(input []Status, currentPosition, targetPosition int) []Status {
	var shuffle shuffleDirection

	if targetPosition < currentPosition {
		// affected elements will need to shuffle backwards if the focused
		// element moves towards the beginning of the list...
		shuffle = backwards
	} else {
		// ...or else the elements need to shuffle forwards if the focused
		// element moves towards the end of the list.
		shuffle = forwards
	}

	output := make([]Status, len(input))

	for ind := range input {
		switch {
		case (shuffle == backwards) && (ind < targetPosition || ind > currentPosition):
			output[ind] = input[ind]
		case (shuffle == backwards) && (ind == currentPosition):
			output[targetPosition] = input[ind]
		case (shuffle == backwards):
			output[ind+1] = input[ind]
		case (shuffle == forwards) && (ind < currentPosition || ind > targetPosition):
			output[ind] = input[ind]
		case (shuffle == forwards) && (ind == currentPosition):
			output[targetPosition] = input[ind]
		case (shuffle == forwards):
			output[ind-1] = input[ind]
		}
	}

	return output
}