/**
 * Beispiel aus
 *
 * - Algorithmen und Datenstrukturen für Dummies
 *   - von Andreas Gogol-Döring und Thomas Letschert
 *   - Verlag Wiley-VCH; Oktober 2019
 *  - Kapitel 4, Listen: Immer einer nach dem anderen
 *
 * @author A. Gogol-Döring, Th. Letschert
 */

import Foundation

struct AuD_04_02_Queue_Imp {

    enum QueueError: Error {
        case Empty
        case Full
    }

    struct Queue {

        class Cell {
            let content: Int
            var next: Cell?
            init (content: Int, next: Cell?) {
                self.content = content
                self.next = next
            }
        }

        static var queueHead: Cell? = nil
        static var queueEnd: Cell? = nil

        static func Enqueue(x: Int) {
            let newCellPtr = Cell(content: x, next: nil)
            if (queueHead == nil) {
                queueHead = newCellPtr
                queueEnd = newCellPtr
            } else {
                queueEnd?.next = newCellPtr
                queueEnd = newCellPtr
            }
        }

        static func Dequeue() throws -> Int {
            guard let firstCell = queueHead else {
                throw QueueError.Empty
            }
            if (firstCell.next == nil) {
                queueHead = nil
                queueEnd = nil
            } else {
                queueHead = queueHead?.next
            }
            return firstCell.content
        }

    }

    static func run() {
        for i in 1 ... 10 {
            Queue.Enqueue(x: i)
        }
        for _ in 1 ... 10 {
            do {
                try print(Queue.Dequeue())
            } catch {
                print("Failed")
            }
        }
    }

}