/*
 * LeaseManager.java May 2004
 *
 * Copyright (C) 2004, Niall Gallagher <niallg@users.sf.net>
 *
 * 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.simpleframework.util.lease;

import java.util.concurrent.TimeUnit;

/**
 * The <code>LeaseManager</code> is used to issue a lease for a named resource.
 * This is effectively used to issue a request for a keyed resource to be
 * released when a lease has expired. The use of a <code>Lease</code> simplifies
 * the interface to the notification and also enables other objects to manage
 * the lease without any knowledge of the resource it represents.
 * 
 * @author Niall Gallagher
 */
public class LeaseManager<T> implements LeaseProvider<T> {

    /**
     * This is the controller used to handle lease operations.
     */
    private Controller<T> handler;

    /**
     * Constructor for the <code>LeaseManager</code> object. This instance is
     * created using a specified notification handler. The specified
     * <code>Cleaner</code> will be notified when the lease for a named resource
     * expires, which will allow the cleaner object to perform a clean up for
     * that resource.
     * 
     * @param cleaner
     *            the cleaner object receiving notifications
     */
    public LeaseManager(Cleaner<T> cleaner) {
        this.handler = new Maintainer<T>(cleaner);
    }

    /**
     * This method will issue a <code>Lease</code> object that can be used to
     * manage the release of a keyed resource. If the lease duration expires
     * before it is renewed then the notification is sent, typically to a
     * <code>Cleaner</code> implementation, to signify that the resource should
     * be recovered. The issued lease can also be canceled.
     * 
     * @param key
     *            this is the key for the leased resource
     * @param duration
     *            this is the duration of the issued lease
     * @param unit
     *            this is the time unit to issue the lease with
     * 
     * @return a lease that can be used to manage notification
     */
    @Override
    public Lease<T> lease(T key, long duration, TimeUnit unit) {
        Contract<T> contract = new Entry<T>(key, duration, unit);

        try {
            this.handler.issue(contract);
        } catch (Exception e) {
            return null;
        }
        return new ContractLease<T>(this.handler, contract);
    }

    /**
     * This is used to close the lease provider such that all of the outstanding
     * leases are canceled. This also ensures the provider can no longer be used
     * to issue new leases, such that further invocations of the
     * <code>lease</code> method will result in null leases. Once the provider
     * has been closes all threads and other such resources are released.
     */
    @Override
    public void close() {
        try {
            this.handler.close();
        } catch (Exception e) {
            return;
        }
    }
}