/*
 * (c) Copyright IBM Corp. 2000, 2001.
 * All Rights Reserved.
 */
package org.eclipse.compare.structuremergeviewer;

import org.eclipse.compare.ITypedElement;
import org.eclipse.swt.graphics.Image;

/**
 * Interface for objects used as input to a two-way or three-way compare viewer.
 * It defines API for accessing the three sides for the compare,
 * and a name and image which is used when displaying the three way input
 * in the UI, for example, in a title bar.
 * <p>
 * Note: at most two sides of an <code>ICompareInput</code> can be <code>null</code>,
 * (as it is normal for additions or deletions) but not all three.
 * <p>
 * <code>ICompareInput</code> provides methods for registering
 * <code>ICompareInputChangeListener</code>s
 * that get informed if one (or more)
 * of the three sides of an <code>ICompareInput</code> object changes its value.
 * <p>
 * For example when accepting an incoming addition
 * the (non-<code>null</code>) left side of an <code>ICompareInput</code>
 * is copied to the right side by means of method <code>copy</code>.
 * This should trigger a call to <code>compareInputChanged</code> of registered
 * <code>ICompareInputChangeListener</code>s. 
 * <p>
 * Clients can implement this interface, or use the convenience implementation 
 * <code>DiffNode</code>.
 * </p>
 * 
 * @see StructureDiffViewer
 * @see org.eclipse.compare.contentmergeviewer.ContentMergeViewer
 * @see DiffNode
 */
public interface ICompareInput {

	/**
	 * Returns name of input.
	 * This name is displayed when this input is shown in a viewer.
	 * In many cases this name is the name of one of the non-<code>null</code> sides or a combination
	 * thereof.
	 *
	 * @return name of input
	 */
	String getName();
	
	/**
	 * Returns an image representing this input.
	 * This image is typically displayed when this input is shown in a viewer.
	 * In many cases this image is the image of one of the non-<code>null</code> sides.
	 *
	 * @return image representing this input, or <code>null</code> if no icon should be shown
	 */
	Image getImage();

	/**
	 * Returns the kind of difference between the
	 * three sides ancestor, left and right.
	 * This field is only meaningful if the <code>ICompareInput</code>
	 * is the result of another compare. In this case it is used
	 * together with <code>getImage</code> to compose a icon
	 * which reflects the kind of difference between the two or three elements.
	 *
	 * @return kind of difference (see <code>Differencer</code>)
	 */
	int getKind();
	
	/**
	 * Returns the ancestor side of this input.
	 * Returns <code>null</code> if this input has no ancestor
	 * or in the two-way compare case.
	 *
	 * @return the ancestor of this input, or <code>null</code>
	 */
	ITypedElement getAncestor();
	
	/**
	 * Returns the left side of this input.
	 * Returns <code>null</code> if there is no left side (deletion or addition).
	 *
	 * @return the left side of this input, or <code>null</code>
	 */
	ITypedElement getLeft();
	
	/**
	 * Returns the right side of this input.
	 * Returns <code>null</code> if there is no right side (deletion or addition).
	 *
	 * @return the right side of this input, or <code>null</code>
	 */
	ITypedElement getRight();
	
	/**
	 * Registers the given listener for notification.
	 * If the identical listener is already registered the method has no effect.
	 *
	 * @param listener the listener to register for changes of this input
	 */
	void addCompareInputChangeListener(ICompareInputChangeListener listener);
	
	/**
	 * Unregisters the given listener.
	 * If the identical listener is not registered the method has no effect.
	 *
	 * @param listener the listener to unregister
	 */
	void removeCompareInputChangeListener(ICompareInputChangeListener listener);
	
	/**
	 * Copy one side (source) to the other side (destination) depending on the 
	 * value of <code>leftToRight</code>. This method is called from
	 * a merge viewer if a corresponding action ("take left" or "take right")
	 * has been pressed.
	 * <p>
	 * The implementation should handle the following cases:
	 * <UL>
	 * <LI>
	 * if the source side is <code>null</code> the destination must be deleted,
	 * <LI>
	 * if the destination is <code>null</code> the destination must be created
	 * and filled with the contents from the source,
	 * <LI>
	 * if both sides are non-<code>null</code> the contents of source must be copied to destination.
	 * </UL>
	 * In addition the implementation should send out notification to the registered
	 * <code>ICompareInputChangeListener</code>.
	 * 
	 * @param leftToRight if <code>true</code> the left side is copied to the right side.
	 * If <code>false</code> the right side is copied to the left side
	 */
	void copy(boolean leftToRight);
}