/*
 * 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.usergrid.lock;


import java.io.IOException;
import java.net.ServerSocket;


/**
 * A lock that will work across multiple processes and threads on the same machine. This uses The file system to attempt
 * to obtain a lock.  No blocking is performed, the lock is either successful or fails
 */
public class MultiProcessLocalLock {

    private final int socketNumber;
    private ServerSocket lock;


    /**
     * The filename to use as the lock
     */
    public MultiProcessLocalLock( final int socketNumber ) {
        this.socketNumber = socketNumber;
    }


    /**
     * Attempts to lock the file.  If a lock cannot be acquired, false is returned.  Otherwise, true is returned.
     *
     * @return true if the lock was acquired.  False otherwise.
     */
    public boolean tryLock() throws IOException {

        if ( lock != null ) {
            throw new IllegalStateException( "You already have a lock, you cannot get a lock again" );
        }

        try {
            lock = new ServerSocket( socketNumber );
        }
        catch ( IOException ioe ) {
            //swallow, we didn't get the lock
            return false;
        }


        return true;
    }


    /**
     * Release the lock if we hold it.
     */
    public void releaseLock() throws IOException {
        if ( lock == null ) {
            throw new IllegalStateException( "You cannot release a lock you do not have" );
        }


        lock.close();

        lock = null;
    }


    /**
     * Return true if this instance has the lock
     */
    public boolean hasLock() {
        return lock != null;
    }


    /**
     * Releases the lock if we have it, otherwise is a no-op.
     *
     * @return true if we had the lock and released it.  False if we didn't have the lock
     */
    public boolean maybeReleaseLock() throws IOException {

        if ( lock == null ) {
            return false;
        }

        releaseLock();

        return true;
    }
}