/*
 * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
 * and other copyright owners as documented in the project's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 *
 * - Neither the name of the Eclipse Foundation, Inc. nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.eclipse.jgit.transport;

import com.jcraft.jsch.JSchException;
import com.jcraft.jsch.Session;

/**
 * Creates and destroys SSH connections to a remote system.
 * <p>
 * Different implementations of the session factory may be used to control
 * communicating with the end-user as well as reading their personal SSH
 * configuration settings, such as known hosts and private keys.
 * <p>
 * A {@link Session} must be returned to the factory that created it. Callers
 * are encouraged to retain the SshSessionFactory for the duration of the period
 * they are using the Session.
 */
public abstract class SshSessionFactory {
	private static SshSessionFactory INSTANCE = new DefaultSshSessionFactory();

	/**
	 * Get the currently configured JVM-wide factory.
	 * <p>
	 * A factory is always available. By default the factory will read from the
	 * user's <code>$HOME/.ssh</code> and assume OpenSSH compatibility.
	 *
	 * @return factory the current factory for this JVM.
	 */
	public static SshSessionFactory getInstance() {
		return INSTANCE;
	}

	/**
	 * Change the JVM-wide factory to a different implementation.
	 *
	 * @param newFactory
	 *            factory for future sessions to be created through. If null the
	 *            default factory will be restored.s
	 */
	public static void setInstance(final SshSessionFactory newFactory) {
		if (newFactory != null)
			INSTANCE = newFactory;
		else
			INSTANCE = new DefaultSshSessionFactory();
	}

	/**
	 * Open (or reuse) a session to a host.
	 * <p>
	 * A reasonable UserInfo that can interact with the end-user (if necessary)
	 * is installed on the returned session by this method.
	 * <p>
	 * The caller must connect the session by invoking <code>connect()</code>
	 * if it has not already been connected.
	 *
	 * @param user
	 *            username to authenticate as. If null a reasonable default must
	 *            be selected by the implementation. This may be
	 *            <code>System.getProperty("user.name")</code>.
	 * @param pass
	 *            optional user account password or passphrase. If not null a
	 *            UserInfo that supplies this value to the SSH library will be
	 *            configured.
	 * @param host
	 *            hostname (or IP address) to connect to. Must not be null.
	 * @param port
	 *            port number the server is listening for connections on. May be <=
	 *            0 to indicate the IANA registered port of 22 should be used.
	 * @return a session that can contact the remote host.
	 * @throws JSchException
	 *             the session could not be created.
	 */
	public abstract Session getSession(String user, String pass, String host,
			int port) throws JSchException;

	/**
	 * Close (or recycle) a session to a host.
	 *
	 * @param session
	 *            a session previously obtained from this factory's
	 *            {@link #getSession(String,String, String, int)} method.s
	 */
	public void releaseSession(final Session session) {
		if (session.isConnected())
			session.disconnect();
	}
}