/*******************************************************************************
 * Copyright (c) 2003, 2005 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.osgi.service.resolver;

/**
 * BundleDeltas represent the changes related to an individual bundle between two
 * states.
 * <p>
 * Clients may implement this interface.
 * </p>
 * @since 3.1
 */
public interface BundleDelta extends Comparable {

	/**
	 * Delta type constant (bit mask) indicating that the bundle has been added
	 * to the new state. 
	 * @see BundleDelta#getType
	 */
	public static final int ADDED = 0x1;
	/**
	 * Delta type constant (bit mask) indicating that the bundle is no longer present in 
	 * the new state.
	 * @see BundleDelta#getType
	 */
	public static final int REMOVED = 0x2;
	/**
	 * Delta type constant (bit mask) indicating that the bundle has been updated
	 * between the old and new state.  Note that an update delta may in fact represent
	 * a downgrading of the bundle to a previous version. 
	 * @see BundleDelta#getType
	 */
	public static final int UPDATED = 0x4;
	/**
	 * Delta type constant (bit mask) indicating that the bundle has become resolved
	 * in the new state.  
	 * @see BundleDelta#getType
	 */
	public static final int RESOLVED = 0x8;
	/**
	 * Delta type constant (bit mask) indicating that the bundle has become unresolved
	 * in the new state. Note that newly added bundles are unresolved by default and 
	 * as such, do not transition to unresolved state so this flag is not set.
	 * @see BundleDelta#getType
	 */
	public static final int UNRESOLVED = 0x10;
	/**
	 * Delta type constant (bit mask) indicating that the bundles and packages which this
	 * bundle requires/imports (respectively) have changed in the new state.
	 * @see BundleDelta#getType
	 * @deprecated this type is no longer valid
	 */
	public static final int LINKAGE_CHANGED = 0x20;

	/**
	 * Delta type constant (bit mask) indicating that the bundles which this
	 * bundle optionally requires have changed in the new state.
	 * @see BundleDelta#getType
	 * @deprecated this type is no longer valid
	 */
	public static final int OPTIONAL_LINKAGE_CHANGED = 0x40;

	/**
	 * Delta type constant (bit mask) indicating that the this bundle is
	 * pending a removal.  Note that bundles with this flag set will also
	 * have the {@link BundleDelta#REMOVED} flag set.  A bundle will have
	 * this flag set if it has been removed from the state but has other 
	 * existing bundles in the state that depend on it.
	 * @see BundleDelta#getType
	 */
	public static final int REMOVAL_PENDING = 0x80;

	/**
	 * Delta type constant (bit mask) indicating that the this bundle has
	 * completed a pending removal.  A bundle will complete a pending removal only
	 * after it has been re-resolved by the resolver. 
	 */
	public static final int REMOVAL_COMPLETE = 0x100;

	/**
	 * Returns the BundleDescription that this bundle delta is for.
	 * @return the BundleDescription that this bundle delta is for. 
	 */
	public BundleDescription getBundle();

	/**
	 * Returns the type of change which occured.  The return value is composed
	 * of by bit-wise masking the relevant flags from the set ADDED, REMOVED, 
	 * UPDATED, RESOLVED, UNRESOLVED, LINKAGE_CHANGED, REMOVAL_PENDING, REMOVAL_COMPLETE. 
	 * Note that bundle start and stop state changes are not captured in the 
	 * delta as they do not represent structural changes but rather transient
	 * runtime states.
	 * @return the type of change which occured
	 */
	public int getType();

	/**
	 * Answers an integer indicating the relative positions of the receiver and
	 * the argument in the natural order of elements of the receiver's class.
	 * <p>
	 * The natural order of elements is determined by the bundle id of the
	 * BundleDescription that this bundle delta is for.
	 * 
	 * @return int which should be <0 if the receiver should sort before the
	 *         argument, 0 if the receiver should sort in the same position as
	 *         the argument, and >0 if the receiver should sort after the
	 *         argument.
	 * @param obj
	 *            another BundleDelta an object to compare the receiver to
	 * @exception ClassCastException
	 *                if the argument can not be converted into something
	 *                comparable with the receiver.
	 */
	public int compareTo(Object obj);
}
