/*******************************************************************************
 * Copyright (c) 2011 Nokia and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *   Nokia - Initial API and implementation. Aug 29, 2011
 *******************************************************************************/

package org.eclipse.cdt.debug.edc.internal;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

import org.eclipse.cdt.debug.edc.internal.symbols.files.FileStatistics;
import org.eclipse.cdt.utils.ERandomAccessFile;

/**
 * This class manages open, close and random access of a file. Currently only
 * read operation is allowed.
 * 
 * The most important trait of the class is the file will be auto closed after
 * it's not accessed for a certain period. This is intended for cases like this:
 * release an executable/symbol file after debug so that user can rebuild it.
 */
public class FileAccessor {
	/**
	 * Global cache 
	 */
	static private Map<File, FileAccessor> accessors = Collections.synchronizedMap(new HashMap<File, FileAccessor>());

	/**
	 * Timeout on when to close the file (release the file handle).
	 */
	static final private long TIME_OUT = 3000;	// ms
	
	private final boolean DEBUG = false;

	private RandomAccessFile raFile = null;
	private File file = null;
		
	private long fileAccessTime = 0;
	private Boolean accessingFile = true;

	/**
	 * Monitor thread: if a file has not been accessed for certain time, close it.
	 */
	class MonitorThread extends Thread {

		public MonitorThread() {
			super();
			setDaemon(true);
			setName("File Monitor");
		}

		@Override
		public void run() {
			while (true) {
				synchronized (accessingFile) {
					if (fileAccessTime != 0 && 
							System.currentTimeMillis() > fileAccessTime + TIME_OUT) 
					{
						close();
						fileAccessTime = 0;
						break;  // exit the thread
					}
				}
				
				try {
					sleep(300);
				} catch (InterruptedException e) {
					break;
				}
			}
		}
	}

	/**
	 * Get the {@link FileAccessor} object for the given file.
	 * 
	 * @param osFile
	 *            can be null.
	 * @return cached {@link FileAccessor} object for the file, or create a new
	 *         one if not cached. <code>null</code> if osFile is null.
	 */
	static public FileAccessor getFileAccessor(File osFile) {
		if (osFile == null)
			return null;
		
		FileAccessor ret = accessors.get(osFile);
		if (ret == null) {
			ret = new FileAccessor(osFile);
			accessors.put(osFile, ret);
		}
		
		return ret;
	}
	
	private FileAccessor(File osFile) {
		this.file = osFile;
	}

	public void dispose() {
		synchronized (accessingFile) {
			close();
		}
		
		accessors.remove(file);
	}

	/**
	 * Read bytes from given offset in the file.
	 * 
	 * @param buffer
	 *            caller allocated buffer to hold data.
	 * @param sourceOffset
	 *            offset in the file (in bytes)
	 * @param count
	 *            number of bytes to read
	 * @throws IOException file access failure.
	 */
	public void read(byte[] buffer, long sourceOffset, int count) throws IOException {
		synchronized (accessingFile) {
			ensureOpen();
			
			raFile.seek(sourceOffset);
			raFile.read(buffer, 0, count);
			
			fileAccessTime = System.currentTimeMillis();
		}
	}

	private void ensureOpen() throws IOException {
		if (raFile == null && file != null) {
			if (DEBUG) System.out.println("Thread " + Thread.currentThread().getName() + ": Opening " + file);
			FileStatistics.executablesOpened++;
			FileStatistics.executablesOpen++;
			raFile = new ERandomAccessFile(file, "r");
			
			new MonitorThread().start();	// start the monitor thread
		}
	}

	private void close() {
		if (raFile != null && file != null) {
			try {
				if (DEBUG) System.out.println("File Monitor Thread " + Thread.currentThread().getId() + ": closing " + file);
				FileStatistics.executablesOpen--;
				raFile.close();
				raFile = null;
			} catch (IOException e) {
				// ignore
			}
		}
	}
	
}