function Queue () {
this.head = new Item('head', null)
}
module.exports = Queue
Queue.prototype.append = function append (kind, value) {
var item = new Item(kind, value)
this.head.prepend(item)
return item
}
Queue.prototype.isEmpty = function isEmpty () {
return this.head.prev === this.head
}
Queue.prototype.first = function first () {
return this.head.next
}
function Item (kind, value) {
this.prev = this
this.next = this
this.kind = kind
this.value = value
}
Item.prototype.prepend = function prepend (other) {
other.prev = this.prev
other.next = this
other.prev.next = other
other.next.prev = other
}
Item.prototype.dequeue = function dequeue () {
var prev = this.prev
var next = this.next
prev.next = next
next.prev = prev
this.prev = this
this.next = this
return this.value
}
Item.prototype.isEmpty = function isEmpty () {
return this.prev === this
}