Which XXX completes the InsertAfter$()$ function in the C$++$ LinkedList class for a doubly$-$linked list?

void InsertAfter$($Node$*$ currentNode, Node$*$ newNode$)\{$

if $($head $=$ nullptr$)\{$

head $=$ newNode;

tail $=$ newNode;

$\}$

else if $($currentNode $=$ tail$)\{$

tail $$ next $=$ newllode;

newlNode $$ previous $=$ tail;

$\}$

tall $=$ newNode;

else $\{$

Node$*$ successor $=$ currentNode$->$next;

newNode $$ next $=$ successor;

newNode $$ previous $=$ currentNode;

currentNode$->$next $=$ newNode;

xxX

$\}$

$\}.$

successor $-$ mext $=$ newNode;

successor$-$sprevious $=$ newNode;

currentNode$->$previous $=$ newNode;

currentilode$->$previous $=$ successor;