/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.shiro.session;

import java.io.Serializable;
import java.util.Collection;
import java.util.Date;

/**
 * A {@code Session} is a stateful data context associated with a single Subject (user, daemon process,
 * etc) who interacts with a software system over a period of time.
 * <p/>
 * A {@code Session} is intended to be managed by the business tier and accessible via other
 * tiers without being tied to any given client technology.  This is a <em>great</em> benefit to Java
 * systems, since until now, the only viable session mechanisms were the
 * {@code javax.servlet.http.HttpSession} or Stateful Session EJB's, which many times
 * unnecessarily coupled applications to web or ejb technologies.
 *
 * @since 0.1
 */
public interface Session {

    /**
     * Returns the unique identifier assigned by the system upon session creation.
     * <p/>
     * All return values from this method are expected to have proper {@code toString()},
     * {@code equals()}, and {@code hashCode()} implementations. Good candidates for such
     * an identifier are {@link java.util.UUID UUID}s, {@link java.lang.Integer Integer}s, and
     * {@link java.lang.String String}s.
     *
     * @return The unique identifier assigned to the session upon creation.
     */
    Serializable getId();

    /**
     * Returns the time the session was started; that is, the time the system created the instance.
     *
     * @return The time the system created the session.
     */
    Date getStartTimestamp();

    /**
     * Returns the last time the application received a request or method invocation from the user associated
     * with this session.  Application calls to this method do not affect this access time.
     *
     * @return The time the user last interacted with the system.
     * @see #touch()
     */
    Date getLastAccessTime();

    /**
     * Returns the time in milliseconds that the session session may remain idle before expiring.
     * <ul>
     * <li>A negative return value means the session will never expire.</li>
     * <li>A non-negative return value (0 or greater) means the session expiration will occur if idle for that
     * length of time.</li>
     * </ul>
     * <b>*Note:</b> if you are used to the {@code HttpSession}'s {@code getMaxInactiveInterval()} method, the scale on
     * this method is different: Shiro Sessions use millisecond values for timeout whereas
     * {@code HttpSession.getMaxInactiveInterval} uses seconds.  Always use millisecond values with Shiro sessions.
     *
     * @return the time in milliseconds the session may remain idle before expiring.
     * @throws InvalidSessionException if the session has been stopped or expired prior to calling this method.
     * @since 0.2
     */
    long getTimeout() throws InvalidSessionException;

    /**
     * Sets the time in milliseconds that the session may remain idle before expiring.
     * <ul>
     * <li>A negative value means the session will never expire.</li>
     * <li>A non-negative value (0 or greater) means the session expiration will occur if idle for that
     * length of time.</li>
     * </ul>
     * <p/>
     * <b>*Note:</b> if you are used to the {@code HttpSession}'s {@code getMaxInactiveInterval()} method, the scale on
     * this method is different: Shiro Sessions use millisecond values for timeout whereas
     * {@code HttpSession.getMaxInactiveInterval} uses seconds.  Always use millisecond values with Shiro sessions.
     *
     * @param maxIdleTimeInMillis the time in milliseconds that the session may remain idle before expiring.
     * @throws InvalidSessionException if the session has been stopped or expired prior to calling this method.
     * @since 0.2
     */
    void setTimeout(long maxIdleTimeInMillis) throws InvalidSessionException;

    /**
     * Returns the host name or IP string of the host that originated this session, or {@code null}
     * if the host is unknown.
     *
     * @return the host name or IP string of the host that originated this session, or {@code null}
     *         if the host address is unknown.
     */
    String getHost();

    /**
     * Explicitly updates the {@link #getLastAccessTime() lastAccessTime} of this session to the current time when
     * this method is invoked.  This method can be used to ensure a session does not time out.
     * <p/>
     * Most programmers won't use this method directly and will instead rely on the last access time to be updated
     * automatically as a result of an incoming web request or remote procedure call/method invocation.
     * <p/>
     * However, this method is particularly useful when supporting rich-client applications such as
     * Java Web Start app, Java or Flash applets, etc.  Although rare, it is possible in a rich-client
     * environment that a user continuously interacts with the client-side application without a
     * server-side method call ever being invoked.  If this happens over a long enough period of
     * time, the user's server-side session could time-out.  Again, such cases are rare since most
     * rich-clients frequently require server-side method invocations.
     * <p/>
     * In this example though, the user's session might still be considered valid because
     * the user is actively &quot;using&quot; the application, just not communicating with the
     * server. But because no server-side method calls are invoked, there is no way for the server
     * to know if the user is sitting idle or not, so it must assume so to maintain session
     * integrity.  This {@code touch()} method could be invoked by the rich-client application code during those
     * times to ensure that the next time a server-side method is invoked, the invocation will not
     * throw an {@link ExpiredSessionException ExpiredSessionException}.  In short terms, it could be used periodically
     * to ensure a session does not time out.
     * <p/>
     * How often this rich-client &quot;maintenance&quot; might occur is entirely dependent upon
     * the application and would be based on variables such as session timeout configuration,
     * usage characteristics of the client application, network utilization and application server
     * performance.
     *
     * @throws InvalidSessionException if this session has stopped or expired prior to calling this method.
     */
    void touch() throws InvalidSessionException;

    /**
     * Explicitly stops (invalidates) this session and releases all associated resources.
     * <p/>
     * If this session has already been authenticated (i.e. the {@code Subject} that
     * owns this session has logged-in), calling this method explicitly might have undesired side effects:
     * <p/>
     * It is common for a {@code Subject} implementation to retain authentication state in the
     * {@code Session}.  If the session
     * is explicitly stopped by application code by calling this method directly, it could clear out any
     * authentication state that might exist, thereby effectively &quot;unauthenticating&quot; the {@code Subject}.
     * <p/>
     * As such, you might consider {@link org.apache.shiro.subject.Subject#logout logging-out} the 'owning'
     * {@code Subject} instead of manually calling this method, as a log out is expected to stop the
     * corresponding session automatically, and also allows framework code to execute additional cleanup logic.
     *
     * @throws InvalidSessionException if this session has stopped or expired prior to calling this method.
     */
    void stop() throws InvalidSessionException;

    /**
     * Returns the keys of all the attributes stored under this session.  If there are no
     * attributes, this returns an empty collection.
     *
     * @return the keys of all attributes stored under this session, or an empty collection if
     *         there are no session attributes.
     * @throws InvalidSessionException if this session has stopped or expired prior to calling this method.
     * @since 0.2
     */
    Collection<Object> getAttributeKeys() throws InvalidSessionException;

    /**
     * Returns the object bound to this session identified by the specified key.  If there is no
     * object bound under the key, {@code null} is returned.
     *
     * @param key the unique name of the object bound to this session
     * @return the object bound under the specified {@code key} name or {@code null} if there is
     *         no object bound under that name.
     * @throws InvalidSessionException if this session has stopped or expired prior to calling
     *                                 this method.
     */
    Object getAttribute(Object key) throws InvalidSessionException;

    /**
     * Binds the specified {@code value} to this session, uniquely identified by the specified
     * {@code key} name.  If there is already an object bound under the {@code key} name, that
     * existing object will be replaced by the new {@code value}.
     * <p/>
     * If the {@code value} parameter is null, it has the same effect as if
     * {@link #removeAttribute(Object) removeAttribute} was called.
     *
     * @param key   the name under which the {@code value} object will be bound in this session
     * @param value the object to bind in this session.
     * @throws InvalidSessionException if this session has stopped or expired prior to calling
     *                                 this method.
     */
    void setAttribute(Object key, Object value) throws InvalidSessionException;

    /**
     * Removes (unbinds) the object bound to this session under the specified {@code key} name.
     *
     * @param key the name uniquely identifying the object to remove
     * @return the object removed or {@code null} if there was no object bound under the name
     *         {@code key}.
     * @throws InvalidSessionException if this session has stopped or expired prior to calling
     *                                 this method.
     */
    Object removeAttribute(Object key) throws InvalidSessionException;
}
