/*
 * Copyright 2006 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.wamblee.io;

import java.io.File;
import java.io.FileFilter;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Monitors a directory for changes. 
 *
 * @author Erik Brakkee
 */
public class DirectoryMonitor {
    
    private static final Log LOG = LogFactory.getLog(DirectoryMonitor.class);
    
    public static interface Listener { 
        void fileChanged(File aFile); 
        void fileCreated(File aFile); 
        void fileDeleted(File aFile);
    };
    
    private File _directory;
    private FileFilter _filter; 
    private Listener _listener;
    private Map<File,Date> _contents; 
    
    public DirectoryMonitor(File aDirectory, FileFilter aFilefilter, Listener aListener) {
        _directory = aDirectory;
        if ( !_directory.isDirectory()) { 
            throw new IllegalArgumentException("Directory '" + _directory + "' does not exist");
        }
        _filter = aFilefilter; 
        _listener = aListener;
        _contents = new HashMap<File,Date>();
    }
    
    public void poll() {
        LOG.debug("Polling " + _directory);
        Map<File,Date> newContents = new HashMap<File,Date>();
        File[] files = _directory.listFiles(_filter);
        for (File file: files) { 
            if ( _contents.containsKey(file)) { 
                Date oldDate = _contents.get(file);
                if (file.lastModified() != oldDate.getTime()) { 
                    _listener.fileChanged(file);
                } else { 
                    // No change. 
                }
                _contents.remove(file);
                newContents.put(file, new Date(file.lastModified()));
            } else { 
                _listener.fileCreated(file);
                newContents.put(file, new Date(file.lastModified()));
            }
        }
        for (File file: _contents.keySet()) { 
            _listener.fileDeleted(file);
        }
        _contents = newContents;
    }

}