Copyright (c) 2000, 2008 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
/*******************************************************************************
 * Copyright (c) 2000, 2008 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.edits;

import org.eclipse.core.runtime.Assert;

import org.eclipse.jface.text.BadLocationException;
import org.eclipse.jface.text.DocumentEvent;
import org.eclipse.jface.text.IDocument;
import org.eclipse.jface.text.IDocumentListener;


class UndoCollector implements IDocumentListener {

	protected UndoEdit undo;
	private int fOffset;
	private int fLength;

	
Since:
3.1/**
	 * @since 3.1
	 */
	private String fLastCurrentText;

	public UndoCollector(TextEdit root) {
		fOffset= root.getOffset();
		fLength= root.getLength();
	}

	public void connect(IDocument document) {
		document.addDocumentListener(this);
		undo= new UndoEdit();
	}

	public void disconnect(IDocument document) {
		if (undo != null) {
			document.removeDocumentListener(this);
			undo.defineRegion(fOffset, fLength);
		}
	}

	@Override
	public void documentChanged(DocumentEvent event) {
		fLength+= getDelta(event);
	}

	private static int getDelta(DocumentEvent event) {
		String text= event.getText();
		return text == null ? -event.getLength() : (text.length() - event.getLength());
	}

	@Override
	public void documentAboutToBeChanged(DocumentEvent event) {
		int offset= event.getOffset();
		int currentLength= event.getLength();
		String currentText= null;
		try {
			currentText= event.getDocument().get(offset, currentLength);
		} catch (BadLocationException cannotHappen) {
			Assert.isTrue(false, "Can't happen"); //$NON-NLS-1$
		}

		/*
		 * see https://bugs.eclipse.org/bugs/show_bug.cgi?id=93634
		 * If the same string is replaced on many documents (e.g. rename
		 * package), the size of the undo can be reduced by using the same
		 * String instance in all edits, instead of using the unique String
		 * returned from IDocument.get(int, int).
		 */
		if (fLastCurrentText != null && fLastCurrentText.equals(currentText))
			currentText= fLastCurrentText;
		else
			fLastCurrentText= currentText;

		String newText= event.getText();
		undo.add(new ReplaceEdit(offset, newText != null ? newText.length() : 0, currentText));
	}
}