package q5

type ListHead struct {
	next *ListHead
	prev *ListHead
	data interface{}
}

func (this *ListHead) Init() {
	this.next = this
	this.prev = this
	this.data = nil
}

func (this *ListHead) Del() {
	this.next.prev = this.prev
	this.prev.next = this.next
}

func (this *ListHead) AddTail(pnew *ListHead) {
	prev := this.prev
	next := this

	next.prev = pnew
	pnew.next = next
	pnew.prev = prev
	prev.next = pnew
}

func (this *ListHead) FirstEntry() interface{} {
	return this.next.data
}

func (this *ListHead) Replace(pnew *ListHead) {
	pnew.next = this.next
	pnew.next.prev = pnew
	pnew.prev = this.prev
	pnew.prev.next = pnew
	pnew.data = this.data
}

func (this *ListHead) ReplaceInit(pnew *ListHead) {
	this.Replace(pnew)
	this.Init()
}

func (this *ListHead) Empty() bool {
	return this.next == this
}

func (this *ListHead) DelInit() {
	this.Del()
	this.Init()
}