Copyright 2010 the original author or authors.
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.
/**
 * Copyright 2010 the original author or authors.
 *
 * 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.I0Itec.zkclient;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import org.I0Itec.zkclient.exception.ZkNoNodeException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

Type parameters:
<T> – 
           The data type that is being watched./**
 * @param <T>
 *            The data type that is being watched.
 */
public final class ContentWatcher<T extends Object> implements IZkDataListener {

    private static final Logger LOG = LoggerFactory.getLogger(ContentWatcher.class);

    private Lock _contentLock = new ReentrantLock(true);
    private Condition _contentAvailable = _contentLock.newCondition();

    private Holder<T> _content;
    private String _fileName;
    private ZkClient _zkClient;

    public ContentWatcher(ZkClient zkClient, String fileName) {
        _fileName = fileName;
        _zkClient = zkClient;
    }

    public void start() {
        _zkClient.subscribeDataChanges(_fileName, this);
        readData();
        LOG.debug("Started ContentWatcher");
    }

    @SuppressWarnings("unchecked")
    private void readData() {
        try {
            setContent((T) _zkClient.readData(_fileName));
        } catch (ZkNoNodeException e) {
            // ignore if the node has not yet been created
        }
    }

    public void stop() {
        _zkClient.unsubscribeDataChanges(_fileName, this);
    }

    public void setContent(T data) {
        LOG.debug("Received new data: " + data);
        _contentLock.lock();
        try {
            _content = new Holder<T>(data);
            _contentAvailable.signalAll();
        } finally {
            _contentLock.unlock();
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public void handleDataChange(String dataPath, Object data) {
        setContent((T) data);
    }

    @Override
    public void handleDataDeleted(String dataPath) {
        // ignore
    }

    public T getContent() throws InterruptedException {
        _contentLock.lock();
        try {
            while (_content == null) {
                _contentAvailable.await();
            }
            return _content.get();
        } finally {
            _contentLock.unlock();
        }
    }
}