#include "list.h"

//////////////////////////////////////////////////////////////////////
//
// swapnode() - swap the position of two given nodes in a list, being
//              sure to appropriately adjust any and all pertinent
//              pointers to ensure list integrity following the
//              operation (including potential changes to the list's
//              own first and last pointers, along with connectivity
//              between the nodes from the start to end of the list).
//
//        note: you are NOT to just adjust node info values. You must
//              disconnect the identified nodes from the list and 
//              reconnect them- the node is our unit of transaction,
//              NOT the data it contains.
//
//    behavior: on a NULL list- do nothing: return NULL
//              on an EMPTY list- do nothing: return list unchanged
//              on a NULL/invalid nodes to swap- do nothing: return
//                  the list unchanged
//
//        note: where applicable, make use of the getpos() and
//              setpos() functions to aid you in accomplishing this
//              task. Don't needlessly reinvent the wheel.
//
//              as with the other functions, you may use no more
//              than one return() statement per function.
//
List *swapnode(List *myList, Node *item1, Node *item2)
{
	if(myList!=NULL)
	{
		if(myList->first!=NULL)
		{
			if(item1!=NULL&&item2!=NULL)
			{
				if(item1!=item2)
				{
					int pos; //declare variables, because swaps needed.
					Node *tmp=NULL;
					if(item1==myList->first)
					{
						if(item2==myList->last)//swapping first and last
						{
							pos=getpos(myList,item2); //mv last to prev
							myList->last=setpos(myList,(pos-1));
							myList->first=myList->first->after;
							item1->after=NULL;  //mv first to after
							myList->last->after=item1;  //mv Item1 to last
							myList->last=item1;      //adjust last to actual last 
						    item2->after=myList->first;//put item 2 before first
							myList->first=item2;//adjust first to actual first
						}
						else //swapping first and where ever in-between
						{
							myList->first=myList->first->after;
							item1->after=item2->after;
							if(item2!=myList->first)//if item 2 didn't become first
							{
								pos=getpos(myList,item2);
/*disconnet I2, connect I1*/	tmp=setpos(myList,(pos-1)); 
								tmp->after=item1;
								item2->after=myList->first; //re-connect item 1
								myList->first=item2; //adjust first to actual first
							}
							else //if item 2 became first
								myList->first->after=item1; //connect item completely
						}
					}
					else if(item2==myList->first) //inverse of if item 2 was first
					{							
						if(item1==myList->last) 
						{
							pos=getpos(myList,item1);
							myList->last=setpos(myList,(pos-1));
							myList->first=myList->first->after;
							item2->after=NULL;
							myList->last->after=item2;
							myList->last=item2;
							item1->after=myList->first;
							myList->first=item1;
						}
						else 
						{
							myList->first=myList->first->after;
							item2->after=item1->after;
							if(item2!=myList->first)
							{
								pos=getpos(myList,item1);
								tmp=setpos(myList,(pos-1));
								tmp->after=item2;
								item1->after=myList->first;
								myList->first=item1;
							}
							else
								myList->first->after=item2;
						}
					}
					else if(item1==myList->last)  //final checks for if they are first or last, checking if a single items last &
					{                                                                              //none are first
							pos=getpos(myList,item1);
							myList->last=setpos(myList,pos-1);
							item1->after=item2->after;  
							myList->last->after=NULL; //moving last back 1 and pointing item 1 to what item 2 points to
							pos=getpos(myList,item2); 
							tmp=setpos(myList,pos-1); 
							tmp->after=item1; //dis-connecting item 2 and totally connecting item 1
							myList->last->after=item2;
							myList->last=item2; //moving item 2 to last pos and re-adjusting last pointer			
					}
					else if(item2==myList->last) //inverse of last check
					{	
						pos=getpos(myList,item2);
						myList->last=setpos(myList,pos-1);
						item2->after=item1->after;
						myList->last->after=NULL;
						pos=getpos(myList,item1);
						tmp=setpos(myList,pos-1);
						tmp->after=item2;
						myList->last->after=item1;
						myList->last=item1;
					}
					else //IF neither nodes are first nor last
					{
						pos=getpos(myList,item1);
						tmp=setpos(myList,(pos-1));
						tmp->after=item1->after;  //disconnect item1
						item1->after=item2->after;
						pos=getpos(myList,item2);
						Node *tmp2=setpos(myList,pos-1); //because tmp still holds place for item 1
						tmp2->after=item1; //re-connecting item1 whilst dis-connecting 2
						item2->after=tmp->after;
						tmp->after=item2;  //re-connecting item to where item 1 was
					}
				}
			}
		}
	}

						


	return(myList);
}