// If the size is exceeded we remove the root element as it is the least used element
private void RemoveIfNecessary()
{
if (GetSize() == maxSize)
{
var tmp = Root.Next;
tmp.Previous = null;
Root = tmp;
}
}
// Add an item in the cache
private LeastRecentlyUsedCacheItem <T> Add(T itemToAdd)
{
// Create the root node
if (Root is null)
{
Root = new LeastRecentlyUsedCacheItem <T>
{
Item = itemToAdd,
Next = null,
Previous = null,
UsedAt = DateTime.UtcNow
};
return(Root);
}
else
{
// Remove an item if the list is full
RemoveIfNecessary();
var tmp = Root;
while (tmp.Next != null)
{
tmp = tmp.Next;
}
// We had the new node at the end as it is the most recently used element
tmp.Next = new LeastRecentlyUsedCacheItem <T>
{
Item = itemToAdd,
Next = null,
Previous = tmp,
UsedAt = DateTime.UtcNow
};
return(tmp);
}
}
// Sort the list from the least used to the most recently used
private void SortList(LeastRecentlyUsedCacheItem <T> root)
{
if (root is null || root.Next is null)
{
return;
}
// If the current node has been used more recently than the next one we swap them
if (root.UsedAt > root.Next.UsedAt)
{
var tmp = root.Next;
var previous = root.Previous;
root.Next = tmp.Next;
root.Previous = tmp;
tmp.Previous = previous;
tmp.Next = previous?.Next ?? root;
// If we swap the first item in the list there is no previous element to it
if (previous != null)
{
previous.Next = tmp;
}
else
{
Root = tmp; // We set the new root of the list
}
// Sort the list with the current node
SortList(root);
}
else
{
// Sort from the next node
SortList(root.Next);
}
}
