rchatham/SwiftyAnimate

//
//  DataStructures.swift
//  Animate
//
//  Created by Reid Chatham on 10/18/16.
//  Copyright © 2016 Reid Chatham. All rights reserved.
//


/// :nodoc:
internal class Node<T> {
    var data: T
    weak var previous: Node<T>?
    var next: Node<T>?
    init(data: T) {
        self.data = data
    }
}

/// :nodoc:
internal struct Queue<T> {
    var first, last: Node<T>?
    mutating func dequeue() -> T? {
        let pop = first?.data
        if first === last {
            first = nil
            last = nil
        } else {
            first = first?.next
        }
        return pop
    }
    mutating func enqueue(data: T) {
        if last == nil {
            first = Node(data: data)
            last = first
        } else {
            let new = Node(data: data)
            new.previous = last
            last!.next = new
            last = new
        }
    }
//    mutating func removeLast() -> T? {
//        let pop = last?.data
//        if first === last {
//            first = nil
//            last = nil
//        } else {
//            last = last?.previous
//        }
//        return pop
//    }
}

//extension Queue {
//    mutating func append(_ queue: Queue) {
//        if last != nil {
//            last?.next = queue.first
//            last = queue.last
//        } else {
//            first = queue.first
//            last = queue.last
//        }
//    }
//}

extension Queue {
    mutating func release() {
        // nodes will be automatically released because of swift's automatic reference counting.
        first = nil
        last = nil
    }
}

extension Queue {
    var copy: Queue<T> {
        var queue = Queue<T>()
        var node = first
        while node != nil {
            queue.enqueue(data: node!.data)
            node = node!.next
        }
        return queue
    }
}