/*******************************************************************************
 * Copyright (c) 2007, 2008 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.equinox.internal.provisional.p2.metadata.repository;

import java.net.URL;
import org.eclipse.core.runtime.IProgressMonitor;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.equinox.internal.provisional.p2.core.ProvisionException;
import org.eclipse.equinox.internal.provisional.p2.core.repository.IRepository;
import org.eclipse.equinox.internal.provisional.p2.core.repository.RepositoryEvent;
import org.eclipse.equinox.internal.provisional.p2.query.IQueryable;

/**
 * The metadata repository manager is used to create, access, and manipulate
 * {@link IMetadataRepository} instances. The manager keeps track of a 
 * set of known repositories, and provides caching of these known repositories
 * to avoid unnecessary loading of repositories from the disk or network.  The
 * manager fires {@link RepositoryEvent}s when the set of known repositories
 * changes.
 * 
 * @noimplement This interface is not intended to be implemented by clients.
 */
public interface IMetadataRepositoryManager extends IQueryable {

	/**
	 * Constant used to indicate that all repositories are of interest.
	 */
	public static final int REPOSITORIES_ALL = 0;

	/**
	 * Constant used to indicate that system repositories are of interest.
	 * @see IRepository#PROP_SYSTEM
	 * @see #getKnownRepositories(int)
	 */
	public static final int REPOSITORIES_SYSTEM = 1 << 0;

	/**
	 * Constant used to indicate that non-system repositories are of interest
	 * @see IRepository#PROP_SYSTEM
	 * @see #getKnownRepositories(int)
	 */
	public static final int REPOSITORIES_NON_SYSTEM = 1 << 1;

	/**
	 * Constant used to indicate that local repositories are of interest.
	 * @see #getKnownRepositories(int)
	 */
	public static final int REPOSITORIES_LOCAL = 1 << 2;

	/**
	 * Repository type for a simple repository based on a URL or local file system location.
	 */
	public static final String TYPE_SIMPLE_REPOSITORY = "org.eclipse.equinox.p2.metadata.repository.simpleRepository"; //$NON-NLS-1$

	/**
	 * Adds a repository to the list of metadata repositories tracked by the repository
	 * manager.
	 * @param location The location of the metadata repository to add
	 */
	public void addRepository(URL location);

	/**
	 * Creates and returns a new empty metadata repository of the given type at 
	 * the given location.
	 * <p>
	 * The resulting repository is <b>not</b> added to the list of repositories tracked by
	 * the repository manager. Clients must make a subsequent call to {@link #addRepository(URL)}
	 * if they want the repository manager to remember the repository for subsequent
	 * load attempts.
	 * </p>
	 * 
	 * @param location the location for the new repository
	 * @param name the name of the new repository
	 * @param type the kind of repository to create
	 * @return the newly created repository
	 * @throws ProvisionException if the repository could not be created.  Reasons include:
	 * <ul>
	 * <li>The repository type is unknown.</li>
	 * <li>There was an error writing to the given repository location.</li>
	 * <li>A repository already exists at that location.</li>
	 * </ul>
	 */
	public IMetadataRepository createRepository(URL location, String name, String type) throws ProvisionException;

	/**
	 * Returns the metadata repository locations known to the repository manager.
	 * <p>
	 * Note that the repository manager does not guarantee that a valid repository
	 * exists at any of the returned locations at any particular moment in time.
	 * A subsequent attempt to load a repository at any of the given locations may
	 * or may not succeed.
	 * 
	 * @param flags an integer bit-mask indicating which repositories should be
	 * returned.  <code>REPOSITORIES_ALL</code> can be used as the mask when
	 * all repositories should be returned.  Where multiple masks are combined, only
	 * the repositories that satisfy all the given criteria are returned. For example,
	 * a flag value of (REPOSITORIES_SYSTEM|REPOSITORIES_LOCAL) will only
	 * return repositories that are both system and local repositories.
	 * 
	 * @return the locations of the repositories managed by this repository manager.
	 * 
	 * @see #REPOSITORIES_ALL
	 * @see #REPOSITORIES_SYSTEM
	 * @see #REPOSITORIES_LOCAL
	 * @see #REPOSITORIES_NON_SYSTEM
	 */
	public URL[] getKnownRepositories(int flags);

	/**
	 * Returns the property associated with the repository at the given URL, 
	 * without loading the repository.
	 * <p>
	 * Note that some properties for a repository can only be
	 * determined when that repository is loaded.  This method will return <code>null</code>
	 * for such properties.  Only values for the properties that are already
	 * known by a repository manager will be returned. 
	 * <p>
	 * If a client wishes to retrieve a property value from a repository 
	 * regardless of the cost of retrieving it, the client should load the 
	 * repository and then retrieve the property from the repository itself.
	 * 
	 * @param location the URL of the repository in question
	 * @param key the String key of the property desired
	 * @return the value of the property, or <code>null</code> if the repository
	 * does not exist, the value does not exist, or the property value 
	 * could not be determined without loading the repository.
	 * 
	 * @see #loadRepository(URL, IProgressMonitor)
	 * @see IRepository#getProperties()
	 * 
	 */
	public String getRepositoryProperty(URL location, String key);

	/**
	 * Loads a repository corresponding to the given URL.  If a repository has
	 * previously been loaded at the given location, the same cached repository
	 * may be returned.
	 * <p>
	 * The resulting repository is added to the list of repositories tracked by
	 * the repository manager. Clients must make a subsequent call to {@link #removeRepository(URL)}
	 * if they do not want the repository manager to remember the repository for subsequent
	 * load attempts.
	 * </p>
	 * 
	 * @param location The location of the repository to load
	 * @param monitor a progress monitor, or <code>null</code> if progress
	 *    reporting is not desired
	 * @return The loaded metadata repository
	 * @throws ProvisionException if the repository could not be created.  Reasons include:
	 * <ul>
	 * <li>There is no existing repository at that location.</li>
	 * <li>The repository at that location could not be read.</li>
	 * </ul>
	 */
	public IMetadataRepository loadRepository(URL location, IProgressMonitor monitor) throws ProvisionException;

	/**
	 * Refreshes the repository corresponding to the given URL. This method discards
	 * any cached state held by the repository manager and reloads the repository
	 * contents. The provided repository location must already be known to the repository
	 * manager.
	 * 
	 * @param location The location of the repository to refresh
	 * @param monitor a progress monitor, or <code>null</code> if progress
	 *    reporting is not desired
	 * @return The refreshed metadata repository
	 * @throws ProvisionException if the repository could not be created.  Reasons include:
	 * <ul>
	 * <li>The location is not known to the repository manager.</li>
	 * <li>There is no existing repository at that location.</li>
	 * <li>The repository at that location could not be read.</li>
	 * </ul>
	 */
	public IMetadataRepository refreshRepository(URL location, IProgressMonitor monitor) throws ProvisionException;

	/**
	 * Removes the metadata repository at the given location from the list of
	 * metadata repositories tracked by the repository manager.  The underlying
	 * repository is not deleted.
	 * 
	 * @param location The location of the repository to remove
	 * @return <code>true</code> if a repository was removed, and 
	 * <code>false</code> otherwise.
	 */
	public boolean removeRepository(URL location);

	/**
	 * Validates a given URL and returns a status indicating whether a valid repository is likely
	 * to be found at the given URL.  Callers must assume that the validity of a 
	 * repository location cannot be completely determined until an attempt to load 
	 * the repository is made.  
	 * 
	 * @param location The location of the repository to validate
	 * @param monitor a progress monitor, or <code>null</code> if progress
	 *    reporting is not desired
	 * @return A status indicating whether a valid repository is likely located at the
	 * location.  A status with severity <code>OK</code> indicates that the repository is
	 * likely to be loadable, or that as much validation as could be done was successful.
	 * Reasons for a non-OK status include:
	 * <ul>
	 * <li>The specified location is not a valid repository location.</li>
	 * <li>There is no existing repository at that location.</li>
	 * <li>The repository at that location could not be read.</li>
	 * </ul>
	 */
	public IStatus validateRepositoryLocation(URL location, IProgressMonitor monitor);
}