PackBitmapIndexRemapper.java

/*
 * Copyright (C) 2013, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.internal.storage.file;

import java.util.Collections;
import java.util.Iterator;
import java.util.NoSuchElementException;

import org.eclipse.jgit.internal.storage.file.BasePackBitmapIndex.StoredBitmap;
import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.BitmapIndex;
import org.eclipse.jgit.lib.ObjectId;

import com.googlecode.javaewah.EWAHCompressedBitmap;
import com.googlecode.javaewah.IntIterator;

/**
 * A PackBitmapIndex that remaps the bitmaps in the previous index to the
 * positions in the new pack index. Note, unlike typical PackBitmapIndex
 * implementations this implementation is not thread safe, as it is intended to
 * be used with a PackBitmapIndexBuilder, which is also not thread safe.
 */
public class PackBitmapIndexRemapper extends PackBitmapIndex
        implements Iterable<PackBitmapIndexRemapper.Entry> {

    private final BasePackBitmapIndex oldPackIndex;
    final PackBitmapIndex newPackIndex;
    private final BitSet inflated;
    private final int[] prevToNewMapping;

    /**
     * A PackBitmapIndex that maps the positions in the prevBitmapIndex to the
     * ones in the newIndex.
     *
     * @param prevBitmapIndex
     *            the bitmap index with the old mapping.
     * @param newIndex
     *            the bitmap index with the new mapping.
     * @return a bitmap index that attempts to do the mapping between the two.
     */
    public static PackBitmapIndexRemapper newPackBitmapIndex(
            BitmapIndex prevBitmapIndex, PackBitmapIndex newIndex) {
        if (!(prevBitmapIndex instanceof BitmapIndexImpl))
            return new PackBitmapIndexRemapper(newIndex);

        PackBitmapIndex prevIndex = ((BitmapIndexImpl) prevBitmapIndex)
                .getPackBitmapIndex();
        if (!(prevIndex instanceof BasePackBitmapIndex))
            return new PackBitmapIndexRemapper(newIndex);

        return new PackBitmapIndexRemapper(
                (BasePackBitmapIndex) prevIndex, newIndex);
    }

    private PackBitmapIndexRemapper(PackBitmapIndex newPackIndex) {
        this.oldPackIndex = null;
        this.newPackIndex = newPackIndex;
        this.inflated = null;
        this.prevToNewMapping = null;
    }

    private PackBitmapIndexRemapper(
            BasePackBitmapIndex oldPackIndex, PackBitmapIndex newPackIndex) {
        this.oldPackIndex = oldPackIndex;
        this.newPackIndex = newPackIndex;
        inflated = new BitSet(newPackIndex.getObjectCount());

        prevToNewMapping = new int[oldPackIndex.getObjectCount()];
        for (int pos = 0; pos < prevToNewMapping.length; pos++)
            prevToNewMapping[pos] = newPackIndex.findPosition(
                    oldPackIndex.getObject(pos));
    }

    /** {@inheritDoc} */
    @Override
    public int findPosition(AnyObjectId objectId) {
        return newPackIndex.findPosition(objectId);
    }

    /** {@inheritDoc} */
    @Override
    public ObjectId getObject(int position) throws IllegalArgumentException {
        return newPackIndex.getObject(position);
    }

    /** {@inheritDoc} */
    @Override
    public int getObjectCount() {
        return newPackIndex.getObjectCount();
    }

    /** {@inheritDoc} */
    @Override
    public EWAHCompressedBitmap ofObjectType(
            EWAHCompressedBitmap bitmap, int type) {
        return newPackIndex.ofObjectType(bitmap, type);
    }

    /** {@inheritDoc} */
    @Override
    public Iterator<Entry> iterator() {
        if (oldPackIndex == null)
            return Collections.<Entry> emptyList().iterator();

        final Iterator<StoredBitmap> it = oldPackIndex.getBitmaps().iterator();
        return new Iterator<>() {
            private Entry entry;

            @Override
            public boolean hasNext() {
                while (entry == null && it.hasNext()) {
                    StoredBitmap sb = it.next();
                    if (newPackIndex.findPosition(sb) != -1)
                        entry = new Entry(sb, sb.getFlags());
                }
                return entry != null;
            }

            @Override
            public Entry next() {
                if (!hasNext())
                    throw new NoSuchElementException();

                Entry res = entry;
                entry = null;
                return res;
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }

    /** {@inheritDoc} */
    @Override
    public EWAHCompressedBitmap getBitmap(AnyObjectId objectId) {
        EWAHCompressedBitmap bitmap = newPackIndex.getBitmap(objectId);
        if (bitmap != null || oldPackIndex == null)
            return bitmap;

        StoredBitmap oldBitmap = oldPackIndex.getBitmaps().get(objectId);
        if (oldBitmap == null)
            return null;

        if (newPackIndex.findPosition(objectId) == -1)
            return null;

        inflated.clear();
        for (IntIterator i = oldBitmap.getBitmapWithoutCaching()
                .intIterator(); i.hasNext();)
            inflated.set(prevToNewMapping[i.next()]);
        bitmap = inflated.toEWAHCompressedBitmap();
        bitmap.trim();
        return bitmap;
    }

    /** An entry in the old PackBitmapIndex. */
    public static final class Entry extends ObjectId {
        private final int flags;

        Entry(AnyObjectId src, int flags) {
            super(src);
            this.flags = flags;
        }

        /** @return the flags associated with the bitmap. */
        public int getFlags() {
            return flags;
        }
    }

    /** {@inheritDoc} */
    @Override
    public int getBitmapCount() {
        // The count is only useful for the end index, not the remapper.
        return 0;
    }
}