public T Shift()
{
Header.Validate(x => x != null, new InvalidOperationException(Messages.DequeEmptyError));
var item = default(T);
if (Header == Header.Previous && Header == Header.Next)
{
item = Header.Entry;
Header = null;
}
else
{
var second = Header.Next;
var last = Header.Previous;
var first = Header;
item = Header.Entry;
last.Next = second;
second.Previous = last;
Header = second;
first.Previous = null;
first.Next = null;
}
return(item);
}
private void MakeHeader(T item)
{
Header = new DoublyLinkedEntry <T>();
Header.Entry = item;
Header.Next = Header;
Header.Previous = Header;
}
public void Append(T item)
{
if (Header == null)
{
MakeHeader(item);
}
else
{
var newEntry = new DoublyLinkedEntry <T>();
newEntry.Entry = item;
newEntry.Previous = Header.Previous;
Header.Previous.Next = newEntry;
Header.Previous = newEntry;
newEntry.Next = Header;
}
}
public T Pop()
{
Header.Validate(x => x != null, new InvalidOperationException(Messages.DequeEmptyError));
var item = default(T);
if (Header == Header.Previous && Header == Header.Next)
{
item = Header.Entry;
Header = null;
}
else
{
var last = Header.Previous;
item = last.Entry;
Header.Previous = last.Previous;
last.Previous.Next = Header;
last.Previous = null;
last.Next = null;
}
return(item);
}
public void Prepend(T item)
{
Append(item);
Header = Header.Previous;
}
