/*******************************************************************************
 * Copyright (c) 2000, 2015 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.text.undo;

import java.util.HashMap;
import java.util.Map;

import org.eclipse.core.runtime.Assert;

import org.eclipse.jface.text.IDocument;


/**
 * This document undo manager registry provides access to a document's
 * undo manager. In order to connect a document a document undo manager
 * call <code>connect</code>. After that call has successfully completed
 * undo manager can be obtained via <code>getDocumentUndoManager</code>.
 * The undo manager is created on the first connect and disposed on the last
 * disconnect, i.e. this registry keeps track of how often a undo manager is
 * connected and returns the same undo manager to each client as long as the
 * document is connected.
 * <p>
 * <em>The recoding of changes starts with the first {@link #connect(IDocument)}.</em></p>
 *
 * @since 3.2
 * @noinstantiate This class is not intended to be instantiated by clients.
 */
public final class DocumentUndoManagerRegistry {

	private static final class Record {
		public Record(IDocument document) {
			count= 0;
			undoManager= new DocumentUndoManager(document);
		}
		private int count;
		private IDocumentUndoManager undoManager;
	}

	private static Map<IDocument, Record> fgFactory= new HashMap<>();

	private DocumentUndoManagerRegistry() {
		// 	Do not instantiate
	}


	/**
	 * Connects the file at the given location to this manager. After that call
	 * successfully completed it is guaranteed that each call to <code>getFileBuffer</code>
	 * returns the same file buffer until <code>disconnect</code> is called.
	 * <p>
	 * <em>The recoding of changes starts with the first {@link #connect(IDocument)}.</em></p>
	 *
	 * @param document the document to be connected
	 */
	public static synchronized void connect(IDocument document) {
		Assert.isNotNull(document);
		Record record= fgFactory.get(document);
		if (record == null) {
			record= new Record(document);
			fgFactory.put(document, record);
		}
		record.count++;
	}

	/**
	 * Disconnects the given document from this registry.
	 *
	 * @param document the document to be disconnected
	 */
	public static synchronized void disconnect(IDocument document) {
		Assert.isNotNull(document);
		Record record= fgFactory.get(document);
		record.count--;
		if (record.count == 0)
			fgFactory.remove(document);

	}

	/**
	 * Returns the file buffer managed for the given location or <code>null</code>
	 * if there is no such file buffer.
	 * <p>
	 * The provided location is either a full path of a workspace resource or
	 * an absolute path in the local file system. The file buffer manager does
	 * not resolve the location of workspace resources in the case of linked
	 * resources.
	 * </p>
	 *
	 * @param document the document for which to get its undo manager
	 * @return the document undo manager or <code>null</code>
	 */
	public static synchronized IDocumentUndoManager getDocumentUndoManager(IDocument document) {
		Assert.isNotNull(document);
		Record record= fgFactory.get(document);
		if (record == null)
			return null;
		return record.undoManager;
	}

}
