package graph.editor;
import graph.*;

/**
 * An interface for a monitor object which cares about when
 * graphs are edited, and can monitor editing operations.  The
 * editor asks the monitor, <i>"Can I do [operation]?"</i>
 * and the monitor returns a boolean value which can allow or
 * disallow the operation. <p>
 *
 * Also, the functions are always called right before an operation
 * is going to be performed, so the monitor can invoke some
 * changes in its internal state which reflect the command if
 * it answers in the affirmative. <p>
 *
 * The interface is sort of clunky in that it contains so
 * many functions, and different entities within your application
 * might want to answer different questions and effect different
 * state changes.  The best way to do this is that your implementation
 * of GraphMonitor can just parsel out the work to one or more other
 * classes/objects.
 *
 * @see Editor
 * @see EditorMonitor
 * @see Graph
 * @see Edge
 * @see Node
 * @author Michael Shilman (michaels@eecs.berkeley.edu)
 * @version $Id$
 */
public interface GraphMonitor {
	/**
	 * This is called when the user tries to add a node
	 * to the graph.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean addNode(Node n);
	
	/**
	 * This is called when the user tries to delete a node
	 * from the graph.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean deleteNode(Node n);
	
	/**
	 * This is called when the user tries to move a node
	 * in the graph.  It expects that the node has not
	 * been moved yet.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean moveNode(Node n, int x, int y);
	
	/**
	 * This is called when the user tries to select a node
	 * in the graph.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean selectNode(Node n);
	
	/**
	 * This is called when the user tries to deselect a node
	 * in the graph.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean deselectNode(Node n);
	
	//Edge monitors=================================================
	
	
	/**
	 * This is called when the user tries to start adding an edge
	 * to the graph.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean startEdge(Edge e, Node tail); 
	
	
	/**
	 * This is called when the user tries to add a edge
	 * to the graph.  The monitor assumes that the current
	 * state of the edge (its <i>head</i> and <i>tail</i>
	 * members) is irrelevant, and only considers the
	 * <i>head</i> and <i>tail</i> arguments to the function.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean addEdge(Edge e, Node tail, Node head);
	
	/**
	 * This is called when the user tries to delete an edge
	 * from the graph.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean deleteEdge(Edge e);
	
	/**
	 * This is called when the user tries to select an edge
	 * in the graph.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean selectEdge(Edge e);
	
	/**
	 * This is called when the user tries to move an
	 * edge from one node to another.  In other words,
	 * if an edge was connecting node <b>A</b> and
	 * node <b>B</b>, and the user tries to move the
	 * edge to connect node <b>A</b> to node <b>C</b>,
	 * then this callback would be called. <p>
	 *
	 * It expects that the <i>head</i> and <i>tail</i>
	 * members be set to what they were <b>before</b>
	 * the move operation is executed.
	 *
	 * @param e		The edge to move
	 * @param from	The original tail (or head) node for the edge
	 * @param to	The proposed new tail (or head) node for the edge
	 * @return	Whether or not to allow the operation.
	 */
	public boolean moveEdge(Edge e, Node from, Node to);
	
	//Graph monitors
	
	/**
	 * This is called when the user tries to add a new
	 * graph.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean addGraph(Graph g);
	
	/**
	 * This is called when the user tries to delete a graph.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean deleteGraph(Graph g);
	
	
	/**
	 * This is called when the user tries to ungroup a graph.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean ungroupGraph(Graph g);
	
	/**
	 * This is called when the user tries to select a graph.
	 *
	 * @return	Whether or not to allow the operation.
	 */
	public boolean selectGraph(Graph g);
}