/*******************************************************************************
 * Copyright (c) 2000, 2003 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials 
 * are made available under the terms of the Common Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/cpl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package net.sourceforge.phpdt.internal.core;

import java.util.Enumeration;

import net.sourceforge.phpdt.core.IBuffer;
import net.sourceforge.phpdt.core.IBufferFactory;
import net.sourceforge.phpdt.core.IJavaElement;
import net.sourceforge.phpdt.core.IOpenable;

import org.eclipse.core.resources.IFile;
import org.eclipse.core.resources.IResource;

/**
 * The buffer manager manages the set of open buffers. It implements an LRU
 * cache of buffers.
 */
public class BufferManager implements IBufferFactory {

	protected static BufferManager DEFAULT_BUFFER_MANAGER;

	/**
	 * LRU cache of buffers. The key and value for an entry in the table is the
	 * identical buffer.
	 */
	protected OverflowingLRUCache openBuffers = new BufferCache(60);

	/**
	 * Creates a new buffer manager.
	 */
	public BufferManager() {
	}

	/**
	 * Adds a buffer to the table of open buffers.
	 */
	protected void addBuffer(IBuffer buffer) {
		openBuffers.put(buffer.getOwner(), buffer);
	}

	/**
	 * @see IBufferFactory#createBuffer(IOpenable)
	 */
	public IBuffer createBuffer(IOpenable owner) {
		IJavaElement element = (IJavaElement) owner;
		IResource resource = element.getResource();
		return new Buffer(resource instanceof IFile ? (IFile) resource : null,
				owner, element.isReadOnly());
	}

	/**
	 * Returns the open buffer associated with the given owner, or
	 * <code>null</code> if the owner does not have an open buffer associated
	 * with it.
	 */
	public IBuffer getBuffer(IOpenable owner) {
		return (IBuffer) openBuffers.get(owner);
	}

	/**
	 * Returns the default buffer manager.
	 */
	public synchronized static BufferManager getDefaultBufferManager() {
		if (DEFAULT_BUFFER_MANAGER == null) {
			DEFAULT_BUFFER_MANAGER = new BufferManager();
		}
		return DEFAULT_BUFFER_MANAGER;
	}

	/**
	 * Returns the default buffer factory.
	 */
	public IBufferFactory getDefaultBufferFactory() {
		return this;
	}

	/**
	 * Returns an enumeration of all open buffers.
	 * <p>
	 * The <code>Enumeration</code> answered is thread safe.
	 * 
	 * @see OverflowingLRUCache
	 * @return Enumeration of IBuffer
	 */
	public Enumeration getOpenBuffers() {
		synchronized (openBuffers) {
			openBuffers.shrink();
			return openBuffers.elements();
		}
	}

	/**
	 * Removes a buffer from the table of open buffers.
	 */
	protected void removeBuffer(IBuffer buffer) {
		openBuffers.remove(buffer.getOwner());
	}
}