DirtyRegionQueue.java

/*******************************************************************************
 * Copyright (c) 2000, 2008 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
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.che.ide.api.editor.reconciler;

import java.util.ArrayList;
import java.util.List;

/**
 * Queue used by {@link ReconcilerWithAutoSave} to manage dirty regions. When a dirty region is inserted into the queue, the queue tries to fold it
 * into the neighboring dirty region.
 */
class DirtyRegionQueue {

    /** The list of dirty regions. */
    private final List<DirtyRegion> fDirtyRegions = new ArrayList<>();

    /** Creates a new empty dirty region. */
    public DirtyRegionQueue() {
        super();
    }

    /**
     * Adds a dirty region to the end of the dirty-region queue.
     *
     * @param dr the dirty region to add
     */
    public void addDirtyRegion(DirtyRegion dr) {
        // If the dirty region being added is directly after the last dirty
        // region on the queue then merge the two dirty regions together.
        final DirtyRegion lastDR = getLastDirtyRegion();
        boolean wasMerged = false;
        if (lastDR != null) {
            if (nullSafeStringsEquals(lastDR.getType(), dr.getType())) {
                if (DirtyRegion.INSERT.equals(lastDR.getType())) {
                    if (lastDR.getOffset() + lastDR.getLength() == dr.getOffset()) {
                        lastDR.mergeWith(dr);
                        wasMerged = true;
                    }
                } else if (DirtyRegion.REMOVE.equals(lastDR.getType())) {
                    if (dr.getOffset() + dr.getLength() == lastDR.getOffset()) {
                        lastDR.mergeWith(dr);
                        wasMerged = true;
                    }
                }
            }
        }

        if (!wasMerged) {
            // Don't merge- just add the new one onto the queue.
            fDirtyRegions.add(dr);
        }
    }

    private static boolean nullSafeStringsEquals(final String s1, final String s2) {
        if (s1 == s2) {
            return true;
        }
        if (s1 == null) {
            return false;
        }
        return s1.equals(s2);
    }

    /**
     * Returns the last dirty region that was added to the queue.
     * 
     * @return the last DirtyRegion on the queue
     */
    private DirtyRegion getLastDirtyRegion() {
        final int size = fDirtyRegions.size();
        return (size == 0 ? null : (DirtyRegion)fDirtyRegions.get(size - 1));
    }

    /**
     * Returns the number of regions in the queue.
     * 
     * @return the dirty-region queue-size
     */
    public int getSize() {
        return fDirtyRegions.size();
    }

    /** Throws away all entries in the queue. */
    public void purgeQueue() {
        fDirtyRegions.clear();
    }

    /**
     * Removes and returns the first dirty region in the queue
     * 
     * @return the next dirty region on the queue
     */
    public DirtyRegion removeNextDirtyRegion() {
        if (fDirtyRegions.size() == 0) {
            return null;
        }
        final DirtyRegion dr = fDirtyRegions.get(0);
        fDirtyRegions.remove(0);
        return dr;
    }
}