/* Copyright 2004, 2005, 2006 Acegi Technology Pty Limited
 *
 * Licensed 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.springframework.security.core.userdetails;

/**
 * Provides a cache of {@link UserDetails} objects.
 *
 * <p>
 * Implementations should provide appropriate methods to set their cache parameters (e.g. time-to-live) and/or force
 * removal of entities before their normal expiration. These are not part of the <code>UserCache</code>
 * interface contract because they vary depending on the type of caching
 * system used (in-memory, disk, cluster, hybrid etc.).
 * <p>
 * Caching is generally only required in applications which do not maintain server-side state, such as remote clients
 * or web services. The authentication credentials are then presented on each invocation and the overhead of accessing
 * a database or other persistent storage mechanism to validate would be excessive. In this case, you would configure
 * a cache to store the <tt>UserDetails</tt> information rather than loading it each time.
 *
 * @see org.springframework.security.authentication.dao.AbstractUserDetailsAuthenticationProvider
 *
 * @author Ben Alex
 */
public interface UserCache {
    //~ Methods ========================================================================================================

    /**
     * Obtains a {@link UserDetails} from the cache.
     *
     * @param username the {@link User#getUsername()} used to place the user in the cache
     *
     * @return the populated <code>UserDetails</code> or <code>null</code> if the user could not be found or if the
     *         cache entry has expired
     */
    UserDetails getUserFromCache(String username);

    /**
     * Places a {@link UserDetails} in the cache. The <code>username</code> is the key used to subsequently
     * retrieve the <code>UserDetails</code>.
     *
     * @param user the fully populated <code>UserDetails</code> to place in the cache
     */
    void putUserInCache(UserDetails user);

    /**
     * Removes the specified user from the cache. The <code>username</code> is the key used to remove the user.
     * If the user is not found, the method should simply return (not thrown an exception).
     * <p>
     * Some cache implementations may not support eviction from the cache, in which case they should provide appropriate
     * behaviour to alter the user in either its documentation, via an exception, or through a log message.
     *
     * @param username to be evicted from the cache
     */
    void removeUserFromCache(String username);
}
