/*
 * Copyright (c) 1997, 2023 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package jakarta.mail;

import jakarta.mail.event.ConnectionEvent;
import jakarta.mail.event.ConnectionListener;
import jakarta.mail.event.MailEvent;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.EventListener;
import java.util.Vector;
import java.util.concurrent.Executor;

/**
 * An abstract class that contains the functionality
 * common to messaging services, such as stores and transports. <p>
 * A messaging service is created from a <code>Session</code> and is
 * named using a <code>URLName</code>.  A service must be connected
 * before it can be used.  Connection events are sent to reflect
 * its connection status.
 *
 * @author Christopher Cotton
 * @author Bill Shannon
 * @author Kanwar Oberoi
 */

public abstract class Service implements AutoCloseable {

    /**
     * The session from which this service was created.
     */
    protected Session session;

    /**
     * The <code>URLName</code> of this service.
     */
    protected volatile URLName url = null;

    /**
     * Debug flag for this service.  Set from the session's debug
     * flag when this service is created.
     */
    protected boolean debug = false;

    private boolean connected = false;

    /*
     * connectionListeners is a Vector, initialized here,
     * because we depend on it always existing and depend
     * on the synchronization that Vector provides.
     * (Sychronizing on the Service object itself can cause
     * deadlocks when notifying listeners.)
     */
    private final Vector<ConnectionListener> connectionListeners
            = new Vector<>();

    /**
     * The queue of events to be delivered.
     */
    private final EventQueue q;

    /**
     * Constructor.
     *
     * @param session Session object for this service
     * @param urlname URLName object to be used for this service
     */
    protected Service(Session session, URLName urlname) {
        this.session = session;
        debug = session.getDebug();
        url = urlname;

        /*
         * Initialize the URLName with default values.
         * The URLName will be updated when connect is called.
         */
        String protocol = null;
        String host = null;
        int port = -1;
        String user = null;
        String password = null;
        String file = null;

        // get whatever information we can from the URL
        // XXX - url should always be non-null here, Session
        //       passes it into the constructor
        if (url != null) {
            protocol = url.getProtocol();
            host = url.getHost();
            port = url.getPort();
            user = url.getUsername();
            password = url.getPassword();
            file = url.getFile();
        }

        // try to get protocol-specific default properties
        if (protocol != null) {
            if (host == null)
                host = session.getProperty("mail." + protocol + ".host");
            if (user == null)
                user = session.getProperty("mail." + protocol + ".user");
        }

        // try to get mail-wide default properties
        if (host == null)
            host = session.getProperty("mail.host");

        if (user == null)
            user = session.getProperty("mail.user");

        // try using the system username
        if (user == null) {
            try {
                user = System.getProperty("user.name");
            } catch (SecurityException sex) {
                // XXX - it's not worth creating a MailLogger just for this
                //logger.log(Level.CONFIG, "Can't get user.name property", sex);
            }
        }

        url = new URLName(protocol, host, port, file, user, password);

        // create or choose the appropriate event queue
        String scope =
                session.getProperties().getProperty("mail.event.scope", "folder");
        Executor executor =
                (Executor) session.getProperties().get("mail.event.executor");
        if (scope.equalsIgnoreCase("application"))
            q = EventQueue.getApplicationEventQueue(executor);
        else if (scope.equalsIgnoreCase("session"))
            q = session.getEventQueue();
        else // if (scope.equalsIgnoreCase("store") ||
            //     scope.equalsIgnoreCase("folder"))
            q = new EventQueue(executor);
    }

    /**
     * A generic connect method that takes no parameters. Subclasses
     * can implement the appropriate authentication schemes. Subclasses
     * that need additional information might want to use some properties
     * or might get it interactively using a popup window. <p>
     *
     * If the connection is successful, an "open" <code>ConnectionEvent</code>
     * is delivered to any <code>ConnectionListeners</code> on this service. <p>
     *
     * Most clients should just call this method to connect to the service.<p>
     *
     * It is an error to connect to an already connected service. <p>
     *
     * The implementation provided here simply calls the following
     * <code>connect(String, String, String)</code> method with nulls.
     *
     * @throws AuthenticationFailedException for authentication failures
     * @throws IllegalStateException         if the service is already connected
     * @throws MessagingException            for other failures
     * @see jakarta.mail.event.ConnectionEvent
     */
    public void connect() throws MessagingException {
        connect(null, null, null);
    }

    /**
     * Connect to the specified address. This method provides a simple
     * authentication scheme that requires a username and password. <p>
     *
     * If the connection is successful, an "open" <code>ConnectionEvent</code>
     * is delivered to any <code>ConnectionListeners</code> on this service. <p>
     *
     * It is an error to connect to an already connected service. <p>
     *
     * The implementation in the Service class will collect defaults
     * for the host, user, and password from the session, from the
     * <code>URLName</code> for this service, and from the supplied
     * parameters and then call the <code>protocolConnect</code> method.
     * If the <code>protocolConnect</code> method returns <code>false</code>,
     * the user will be prompted for any missing information and the
     * <code>protocolConnect</code> method will be called again.  The
     * subclass should override the <code>protocolConnect</code> method.
     * The subclass should also implement the <code>getURLName</code>
     * method, or use the implementation in this class. <p>
     *
     * On a successful connection, the <code>setURLName</code> method is
     * called with a URLName that includes the information used to make
     * the connection, including the password. <p>
     *
     * If the username passed in is null, a default value will be chosen
     * as described above.
     *
     * If the password passed in is null and this is the first successful
     * connection to this service, the user name and the password
     * collected from the user will be saved as defaults for subsequent
     * connection attempts to this same service when using other Service object
     * instances (the connection information is typically always saved within
     * a particular Service object instance).  The password is saved using the
     * Session method <code>setPasswordAuthentication</code>.  If the
     * password passed in is not null, it is not saved, on the assumption
     * that the application is managing passwords explicitly.
     *
     * @param host     the host to connect to
     * @param user     the user name
     * @param password this user's password
     * @throws AuthenticationFailedException for authentication failures
     * @throws IllegalStateException         if the service is already connected
     * @throws MessagingException            for other failures
     * @see jakarta.mail.event.ConnectionEvent
     * @see jakarta.mail.Session#setPasswordAuthentication
     */
    public void connect(String host, String user, String password)
            throws MessagingException {
        connect(host, -1, user, password);
    }

    /**
     * Connect to the current host using the specified username
     * and password.  This method is equivalent to calling the
     * <code>connect(host, user, password)</code> method with null
     * for the host name.
     *
     * @param user     the user name
     * @param password this user's password
     * @throws AuthenticationFailedException for authentication failures
     * @throws IllegalStateException         if the service is already connected
     * @throws MessagingException            for other failures
     * @see jakarta.mail.event.ConnectionEvent
     * @see jakarta.mail.Session#setPasswordAuthentication
     * @see #connect(java.lang.String, java.lang.String, java.lang.String)
     * @since JavaMail 1.4
     */
    public void connect(String user, String password)
            throws MessagingException {
        connect(null, user, password);
    }

    /**
     * Similar to connect(host, user, password) except a specific port
     * can be specified.
     *
     * @param host     the host to connect to
     * @param port     the port to connect to (-1 means the default port)
     * @param user     the user name
     * @param password this user's password
     * @throws AuthenticationFailedException for authentication failures
     * @throws IllegalStateException         if the service is already connected
     * @throws MessagingException            for other failures
     * @see #connect(java.lang.String, java.lang.String, java.lang.String)
     * @see jakarta.mail.event.ConnectionEvent
     */
    public synchronized void connect(String host, int port,
                                     String user, String password) throws MessagingException {

        // see if the service is already connected
        if (isConnected())
            throw new IllegalStateException("already connected");

        PasswordAuthentication pw;
        boolean connected = false;
        boolean save = false;
        String protocol = null;
        String file = null;

        // get whatever information we can from the URL
        // XXX - url should always be non-null here, Session
        //       passes it into the constructor
        if (url != null) {
            protocol = url.getProtocol();
            if (host == null)
                host = url.getHost();
            if (port == -1)
                port = url.getPort();

            if (user == null) {
                user = url.getUsername();
                if (password == null)    // get password too if we need it
                    password = url.getPassword();
            } else {
                if (password == null && user.equals(url.getUsername()))
                    // only get the password if it matches the username
                    password = url.getPassword();
            }

            file = url.getFile();
        }

        // try to get protocol-specific default properties
        if (protocol != null) {
            if (host == null)
                host = session.getProperty("mail." + protocol + ".host");
            if (user == null)
                user = session.getProperty("mail." + protocol + ".user");
        }

        // try to get mail-wide default properties
        if (host == null)
            host = session.getProperty("mail.host");

        if (user == null)
            user = session.getProperty("mail.user");

        // try using the system username
        if (user == null) {
            try {
                user = System.getProperty("user.name");
            } catch (SecurityException sex) {
                // XXX - it's not worth creating a MailLogger just for this
                //logger.log(Level.CONFIG, "Can't get user.name property", sex);
            }
        }

        // if we don't have a password, look for saved authentication info
        if (password == null && url != null) {
            // canonicalize the URLName
            setURLName(new URLName(protocol, host, port, file, user, null));
            pw = session.getPasswordAuthentication(getURLName());
            if (pw != null) {
                if (user == null) {
                    user = pw.getUserName();
                    password = pw.getPassword();
                } else if (user.equals(pw.getUserName())) {
                    password = pw.getPassword();
                }
            } else
                save = true;
        }

        // try connecting, if the protocol needs some missing
        // information (user, password) it will not connect.
        // if it tries to connect and fails, remember why for later.
        AuthenticationFailedException authEx = null;
        try {
            connected = protocolConnect(host, port, user, password);
        } catch (AuthenticationFailedException ex) {
            authEx = ex;
        }

        // if not connected, ask the user and try again
        if (!connected) {
            InetAddress addr;
            try {
                addr = InetAddress.getByName(host);
            } catch (UnknownHostException e) {
                addr = null;
            }
            pw = session.requestPasswordAuthentication(
                    addr, port,
                    protocol,
                    null, user);
            if (pw != null) {
                user = pw.getUserName();
                password = pw.getPassword();

                // have the service connect again
                connected = protocolConnect(host, port, user, password);
            }
        }

        // if we're not connected by now, we give up
        if (!connected) {
            if (authEx != null)
                throw authEx;
            else if (user == null)
                throw new AuthenticationFailedException(
                        "failed to connect, no user name specified?");
            else if (password == null)
                throw new AuthenticationFailedException(
                        "failed to connect, no password specified?");
            else
                throw new AuthenticationFailedException("failed to connect");
        }

        setURLName(new URLName(protocol, host, port, file, user, password));

        if (save)
            session.setPasswordAuthentication(getURLName(),
                    new PasswordAuthentication(user, password));

        // set our connected state
        setConnected(true);

        // finally, deliver the connection event
        notifyConnectionListeners(ConnectionEvent.OPENED);
    }


    /**
     * The service implementation should override this method to
     * perform the actual protocol-specific connection attempt.
     * The default implementation of the <code>connect</code> method
     * calls this method as needed. <p>
     *
     * The <code>protocolConnect</code> method should return
     * <code>false</code> if a user name or password is required
     * for authentication but the corresponding parameter is null;
     * the <code>connect</code> method will prompt the user when
     * needed to supply missing information.  This method may
     * also return <code>false</code> if authentication fails for
     * the supplied user name or password.  Alternatively, this method
     * may throw an AuthenticationFailedException when authentication
     * fails.  This exception may include a String message with more
     * detail about the failure. <p>
     *
     * The <code>protocolConnect</code> method should throw an
     * exception to report failures not related to authentication,
     * such as an invalid host name or port number, loss of a
     * connection during the authentication process, unavailability
     * of the server, etc.
     *
     * @param host     the name of the host to connect to
     * @param port     the port to use (-1 means use default port)
     * @param user     the name of the user to login as
     * @param password the user's password
     * @return true if connection successful, false if authentication failed
     * @throws AuthenticationFailedException for authentication failures
     * @throws MessagingException            for non-authentication failures
     */
    protected boolean protocolConnect(String host, int port, String user,
                                      String password) throws MessagingException {
        return false;
    }

    /**
     * Is this service currently connected? <p>
     *
     * This implementation uses a private boolean field to
     * store the connection state. This method returns the value
     * of that field. <p>
     *
     * Subclasses may want to override this method to verify that any
     * connection to the message store is still alive.
     *
     * @return true if the service is connected, false if it is not connected
     */
    public synchronized boolean isConnected() {
        return connected;
    }

    /**
     * Set the connection state of this service.  The connection state
     * will automatically be set by the service implementation during the
     * <code>connect</code> and <code>close</code> methods.
     * Subclasses will need to call this method to set the state
     * if the service was automatically disconnected. <p>
     *
     * The implementation in this class merely sets the private field
     * returned by the <code>isConnected</code> method.
     *
     * @param connected true if the service is connected,
     *                  false if it is not connected
     */
    protected synchronized void setConnected(boolean connected) {
        this.connected = connected;
    }

    /**
     * Close this service and terminate its connection. A close
     * ConnectionEvent is delivered to any ConnectionListeners. Any
     * Messaging components (Folders, Messages, etc.) belonging to this
     * service are invalid after this service is closed. Note that the service
     * is closed even if this method terminates abnormally by throwing
     * a MessagingException. <p>
     *
     * This implementation uses <code>setConnected(false)</code> to set
     * this service's connected state to <code>false</code>. It will then
     * send a close ConnectionEvent to any registered ConnectionListeners.
     * Subclasses overriding this method to do implementation specific
     * cleanup should call this method as a last step to insure event
     * notification, probably by including a call to <code>super.close()</code>
     * in a <code>finally</code> clause.
     *
     * @throws MessagingException for errors while closing
     * @see jakarta.mail.event.ConnectionEvent
     */
    public synchronized void close() throws MessagingException {
        setConnected(false);
        notifyConnectionListeners(ConnectionEvent.CLOSED);
    }

    /**
     * Return a URLName representing this service.  The returned URLName
     * does <em>not</em> include the password field.  <p>
     *
     * Subclasses should only override this method if their
     * URLName does not follow the standard format. <p>
     *
     * The implementation in the Service class returns (usually a copy of)
     * the <code>url</code> field with the password and file information
     * stripped out.
     *
     * @return the URLName representing this service
     * @see URLName
     */
    public URLName getURLName() {
        URLName url = this.url;    // snapshot
        if (url != null && (url.getPassword() != null || url.getFile() != null))
            return new URLName(url.getProtocol(), url.getHost(),
                    url.getPort(), null /* no file */,
                    url.getUsername(), null /* no password */);
        else
            return url;
    }

    /**
     * Set the URLName representing this service.
     * Normally used to update the <code>url</code> field
     * after a service has successfully connected. <p>
     *
     * Subclasses should only override this method if their
     * URL does not follow the standard format.  In particular,
     * subclasses should override this method if their URL
     * does not require all the possible fields supported by
     * <code>URLName</code>; a new <code>URLName</code> should
     * be constructed with any unneeded fields removed. <p>
     *
     * The implementation in the Service class simply sets the
     * <code>url</code> field.
     *
     * @param url the URLName
     * @see URLName
     */
    protected void setURLName(URLName url) {
        this.url = url;
    }

    /**
     * Add a listener for Connection events on this service. <p>
     *
     * The default implementation provided here adds this listener
     * to an internal list of ConnectionListeners.
     *
     * @param l the Listener for Connection events
     * @see jakarta.mail.event.ConnectionEvent
     */
    public void addConnectionListener(ConnectionListener l) {
        connectionListeners.addElement(l);
    }

    /**
     * Remove a Connection event listener. <p>
     *
     * The default implementation provided here removes this listener
     * from the internal list of ConnectionListeners.
     *
     * @param l the listener
     * @see #addConnectionListener
     */
    public void removeConnectionListener(ConnectionListener l) {
        connectionListeners.removeElement(l);
    }

    /**
     * Notify all ConnectionListeners. Service implementations are
     * expected to use this method to broadcast connection events. <p>
     *
     * The provided default implementation queues the event into
     * an internal event queue. An event dispatcher thread dequeues
     * events from the queue and dispatches them to the registered
     * ConnectionListeners. Note that the event dispatching occurs
     * in a separate thread, thus avoiding potential deadlock problems.
     *
     * @param type the ConnectionEvent type
     */
    protected void notifyConnectionListeners(int type) {
        /*
         * Don't bother queuing an event if there's no listeners.
         * Yes, listeners could be removed after checking, which
         * just makes this an expensive no-op.
         */
        if (connectionListeners.size() > 0) {
            ConnectionEvent e = new ConnectionEvent(this, type);
            queueEvent(e, connectionListeners);
        }

        /* Fix for broken JDK1.1.x Garbage collector :
         *  The 'conservative' GC in JDK1.1.x occasionally fails to
         *  garbage-collect Threads which are in the wait state.
         *  This would result in thread (and consequently memory) leaks.
         *
         * We attempt to fix this by sending a 'terminator' event
         * to the queue, after we've sent the CLOSED event. The
         * terminator event causes the event-dispatching thread to
         * self destruct.
         */
        if (type == ConnectionEvent.CLOSED)
            q.terminateQueue();
    }

    /**
     * Return <code>getURLName.toString()</code> if this service has a URLName,
     * otherwise it will return the default <code>toString</code>.
     */
    @Override
    public String toString() {
        URLName url = getURLName();
        if (url != null)
            return url.toString();
        else
            return super.toString();
    }

    /**
     * Add the event and vector of listeners to the queue to be delivered.
     *
     * @param event  the event
     * @param vector the vector of listeners
     */
    protected void queueEvent(MailEvent event,
                              Vector<? extends EventListener> vector) {
        /*
         * Copy the vector in order to freeze the state of the set
         * of EventListeners the event should be delivered to prior
         * to delivery.  This ensures that any changes made to the
         * Vector from a target listener's method during the delivery
         * of this event will not take effect until after the event is
         * delivered.
         */
        @SuppressWarnings("unchecked")
        Vector<? extends EventListener> v = (Vector<? extends EventListener>) vector.clone();
        q.enqueue(event, v);
    }

    /**
     * Stop the event dispatcher thread so the queue can be garbage collected.
     */
    @Override
    protected void finalize() throws Throwable {
        try {
            q.terminateQueue();
        } finally {
            super.finalize();
        }
    }

    /**
     * Package private method to allow Folder to get the Session for a Store.
     */
    Session getSession() {
        return session;
    }

    /**
     * Package private method to allow Folder to get the EventQueue for a Store.
     */
    EventQueue getEventQueue() {
        return q;
    }
}
