movingPrinter.swift

//: Playground - noun: a place where people can play

struct VirtualPrinter: CustomStringConvertible {
    var sortingIndex: Int
    let name: String

    init(name: String, sortingIndex: Int) {
        self.name = name
        self.sortingIndex = sortingIndex
    }

    var description: String {
        return "\(self.name): \(self.sortingIndex)"
    }
}

var virtualPrinters = [
    VirtualPrinter(name: "A", sortingIndex: 0),
    VirtualPrinter(name: "B", sortingIndex: 1),
    VirtualPrinter(name: "C", sortingIndex: 2),
    VirtualPrinter(name: "D", sortingIndex: 3),
    VirtualPrinter(name: "E", sortingIndex: 4),
]

func moveVirtualPrinter(from srcIndex: Int,
                        to destIndex: Int,
                        inVirtualPrinters printers: [VirtualPrinter]) -> [String: Int] {
    if srcIndex == destIndex {
        return [:]
    }

    var result = [printers[srcIndex].name: destIndex]

    let indexesOfPrintersBetweenMovement: Range<Int>!
    let deltaOfSortingIndex: Int!
    if destIndex > srcIndex { // Down
        indexesOfPrintersBetweenMovement = (srcIndex+1)..<(destIndex+1)
        deltaOfSortingIndex = -1
    } else { // Up
        indexesOfPrintersBetweenMovement = destIndex..<srcIndex
        deltaOfSortingIndex = 1
    }
    for printer in printers[indexesOfPrintersBetweenMovement] {
        result[printer.name] = printer.sortingIndex + deltaOfSortingIndex
    }
    return result
}

moveVirtualPrinter(from: 2, to: 0, inVirtualPrinters: virtualPrinters)
moveVirtualPrinter(from: 1, to: 3, inVirtualPrinters: virtualPrinters)