public class LineList
{
	static final boolean DEBUG=false;
	Node listp;

	public LineList()
	{
		listp=null;
	}

	public InterestingPoint [] Insert(Line line, float x)
	{
		Node node=new Node(line, null);
		Node temp=listp;

   		InterestingPoint[] intersections=new InterestingPoint[2];
		intersections[0]=null;
		intersections[1]=null;

		if(DEBUG) System.out.println("LineList Insert: line "+ line);
		if(listp==null)
		{
			node.up=null;
			node.next=null;
			listp=node;
			return intersections;
		}

		while( temp.next!=null && ((Line)temp.data).YIntersect(x) > line.YIntersect(x) )
		{
			if(DEBUG) System.out.println("LineList Insert: temp.next!=null");
			temp=temp.next;
		}

		if( ((Line)temp.data).YIntersect(x) > line.YIntersect(x) )
		{
			if(DEBUG) System.out.println("LineList Insert: Appending");
			if(temp.next==null)
			{
				node.next=null;
			}else{
				node.next=temp.next;
				node.next.up=node;
			}
			temp.next=node;
			node.up=temp;
			if(node.up==null) if(DEBUG) System.out.println("LineList Insert: line "+line+ " has null up pointer");
		}else{
  			if(DEBUG) System.out.println("LineList Insert: Inserting");
			if(temp==listp)
			{
				if(DEBUG) System.out.println("LineList Insert: temp==listp");
				node.up=null;
				node.next=listp;
				listp.up=node;
				listp=node;
				node.next.up=node;

			}else{
				if(DEBUG) System.out.println("LineList Insert: temp= "+ temp.data+ " ; node = "+node.data);
				node.next=temp;
				node.up=temp.up;
				if(temp.up!=null) temp.up.next=node;
				temp.up=node;
			}
		}

		point p;
		if(node.up!=null)
		{
		    p=line.Intersect( (Line)node.up.data );
			if(p!=null)
    			intersections[0]=new InterestingPoint(line,(Line)node.up.data,p);
		}
		if(node.next!=null)
		{
		    p=line.Intersect( (Line)node.next.data );
			if(p!=null)
    			intersections[1]=new InterestingPoint(line,(Line)node.next.data,p);
		}
		return intersections;
	}

	public InterestingPoint [] Swap(Line l1, Line l2)
	{
		Node temp=listp, up, next;
		InterestingPoint[] ips=new InterestingPoint[2];
		ips[0]=null;ips[1]=null;

		while(temp.data!=(Object)l1 && temp.data!=(Object)l2)
		{
			temp=temp.next;
		}
		Object data;

		data=temp.data;
		temp.data=temp.next.data;
		temp.next.data=data;

		// now we check for new intersections
		point p;
		if(temp.up!=null) 
		{
		    p=((Line)temp.data).Intersect( (Line)temp.up.data );
			if(p!=null)
    			ips[0]=new InterestingPoint((Line)temp.data,(Line)temp.up.data,p);
		}
		if(temp.next.next!=null)
		{
		    p=((Line)temp.next.data).Intersect( (Line)temp.next.next.data );
			if(p!=null)
    			ips[1]=new InterestingPoint((Line)temp.next.data,(Line)temp.next.next.data,p);
		}
		return ips;
	}

	public InterestingPoint Delete(Line line)
	{
		if(DEBUG) System.out.println("LineList Delete: Before: "+this);
		Node temp=listp;
		InterestingPoint ip=null;
		point p;

		if(DEBUG) System.out.println("LineList Delete: Deleting line "+ line);

		while(! ((Line)temp.data).Compare(line) )
			temp=temp.next;

		if(temp==listp)
	    {
			listp=temp.next;
			if(listp!=null && listp.next!=null) listp.next.up=listp;

		}else{
			if(DEBUG) System.out.println("LineList Delete: temp= "+(Line)temp.data);
			if(DEBUG) System.out.println("LineList Delete: temp.up= "+(Line)temp.up.data);
    		temp.up.next=temp.next;
			if(temp.next!=null) temp.next.up=temp.up;
		}
		if(temp.up!=null && temp.next!=null)
		{
		    p=((Line)temp.up.data).Intersect( (Line)temp.next.data );
			if(p!=null)
    			ip=new InterestingPoint((Line)temp.next.data,(Line)temp.up.data,p);
		}
		if(DEBUG) System.out.println("LineList Delete: After: "+this);
		return ip;
	}

	public String toString()
	{
		Node temp=listp;
		StringBuffer s=new StringBuffer("listp->");
		if(listp==null)
			return s.toString();


		s.append("*X*");
		s.append(((Line)listp.data) + "->");

		while(temp.next!=null)
		{
			if(temp.next.up==null) s.append("*X*");
			s.append(((Line)temp.next.data) + "->");
			temp=temp.next;
		}
		s.append("\nBackwards");
		while(temp!=listp)
		{
			s.append(((Line)temp.data) + "->");
			temp=temp.up;
		}
		s.append(((Line)listp.data));

		return s.toString();
	}
}  // LineList