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export default class Queue {
constructor () {
this._first = null
this._last = null
}
push ( value ) {
// An item stores an id and the provided value
var item = value.next ? value : { value: value, next: null, prev: null }
// Deal with the queue being empty or populated
if ( this._last ) {
item.prev = this._last
this._last.next = item
this._last = item
} else {
this._last = item
this._first = item
}
// Update the length and return the current item
return item
}
shift () {
// Check if we have a value
var remove = this._first
if ( !remove ) return null
// If we do, remove it and relink things
this._first = remove.next
if ( this._first ) this._first.prev = null
this._last = this._first ? this._last : null
return remove.value
}
// Shows us the first item in the list
first () {
return this._first && this._first.value
}
// Shows us the last item in the list
last () {
return this._last && this._last.value
}
// Removes the item that was returned from the push
remove ( item ) {
// Relink the previous item
if ( item.prev ) item.prev.next = item.next
if ( item.next ) item.next.prev = item.prev
if ( item === this._last ) this._last = item.prev
if ( item === this._first ) this._first = item.next
// Invalidate item
item.prev = null
item.next = null
}
}
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