/*******************************************************************************
 * Copyright (c) 2000, 2007 IBM Corporation 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
 *
 
 *******************************************************************************/
package org.eclipse.dltk.internal.core;

import java.text.NumberFormat;
import java.util.Enumeration;

import org.eclipse.core.resources.IFile;
import org.eclipse.core.resources.IResource;
import org.eclipse.dltk.core.IBuffer;
import org.eclipse.dltk.core.IModelElement;
import org.eclipse.dltk.core.IOpenable;

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

	protected static BufferManager DEFAULT_BUFFER_MANAGER;
	protected static boolean VERBOSE;

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

	/**
	 * Adds a buffer to the table of open buffers.
	 */
	protected void addBuffer(IBuffer buffer) {
		if (VERBOSE) {
			String owner = ((Openable) buffer.getOwner())
					.toStringWithAncestors();
			System.out.println("Adding buffer for " + owner); //$NON-NLS-1$
		}
		synchronized (this.openBuffers) {
			this.openBuffers.put(buffer.getOwner(), buffer);
		}
		// close buffers that were removed from the cache if space was needed
		this.openBuffers.closeBuffers();
		if (VERBOSE) {
			System.out
					.println("-> Buffer cache filling ratio = " + NumberFormat.getInstance().format(this.openBuffers.fillingRatio()) + "%"); //$NON-NLS-1$//$NON-NLS-2$
		}
	}

	public static IBuffer createBuffer(IOpenable owner) {
		IModelElement element = owner;
		IResource resource = element.getResource();
		return new Buffer(resource instanceof IFile ? (IFile) resource : null,
				owner, element.isReadOnly());
	}

	public static IBuffer createNullBuffer(IOpenable owner) {
		IModelElement element = owner;
		IResource resource = element.getResource();
		return new NullBuffer(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) {
		synchronized (this.openBuffers) {
			return (IBuffer) this.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 an enumeration of all open buffers.
	 * <p>
	 * The <code>Enumeration</code> answered is thread safe.
	 * 
	 * @see OverflowingLRUCache
	 * @return Enumeration of IBuffer
	 */
	public Enumeration getOpenBuffers() {
		Enumeration result;
		synchronized (this.openBuffers) {
			this.openBuffers.shrink();
			result = this.openBuffers.elements();
		}
		// close buffers that were removed from the cache if space was needed
		this.openBuffers.closeBuffers();
		return result;
	}

	/**
	 * Removes a buffer from the table of open buffers.
	 */
	protected void removeBuffer(IBuffer buffer) {
		if (VERBOSE) {
			String owner = ((Openable) buffer.getOwner())
					.toStringWithAncestors();
			System.out.println("Removing buffer for " + owner); //$NON-NLS-1$
		}
		synchronized (this.openBuffers) {
			this.openBuffers.remove(buffer.getOwner());
		}
		// close buffers that were removed from the cache (should be only one)
		this.openBuffers.closeBuffers();
		if (VERBOSE) {
			System.out
					.println("-> Buffer cache filling ratio = " + NumberFormat.getInstance().format(this.openBuffers.fillingRatio()) + "%"); //$NON-NLS-1$//$NON-NLS-2$
		}
	}
}