PackBitmapIndexV1

/*
 * Copyright (C) 2012, 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.io.DataInput;
import java.io.IOException;
import java.io.InputStream;
import java.text.MessageFormat;
import java.util.Arrays;

import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectIdOwnerMap;
import org.eclipse.jgit.util.IO;
import org.eclipse.jgit.util.NB;

import com.googlecode.javaewah.EWAHCompressedBitmap;

/**
 * Support for the pack bitmap index v1 format.
 *
 * @see PackBitmapIndex
 */
class PackBitmapIndexV1 extends BasePackBitmapIndex {
	static final byte[] MAGIC = { 'B', 'I', 'T', 'M' };
	static final int OPT_FULL = 1;

	private static final int MAX_XOR_OFFSET = 126;

	private final PackIndex packIndex;
	private final PackReverseIndex reverseIndex;
	private final EWAHCompressedBitmap commits;
	private final EWAHCompressedBitmap trees;
	private final EWAHCompressedBitmap blobs;
	private final EWAHCompressedBitmap tags;

	private final ObjectIdOwnerMap<StoredBitmap> bitmaps;

	PackBitmapIndexV1(final InputStream fd, PackIndex packIndex,
			PackReverseIndex reverseIndex) throws IOException {
		super(new ObjectIdOwnerMap<StoredBitmap>());
		this.packIndex = packIndex;
		this.reverseIndex = reverseIndex;
		this.bitmaps = getBitmaps();

		final byte[] scratch = new byte[32];
		IO.readFully(fd, scratch, 0, scratch.length);

		// Check the magic bytes
		for (int i = 0; i < MAGIC.length; i++) {
			if (scratch[i] != MAGIC[i]) {
				byte[] actual = new byte[MAGIC.length];
				System.arraycopy(scratch, 0, actual, 0, MAGIC.length);
				throw new IOException(MessageFormat.format(
						JGitText.get().expectedGot, Arrays.toString(MAGIC),
						Arrays.toString(actual)));
			}
		}

		// Read the version (2 bytes)
		final int version = NB.decodeUInt16(scratch, 4);
		if (version != 1)
			throw new IOException(MessageFormat.format(
					JGitText.get().unsupportedPackIndexVersion,
					Integer.valueOf(version)));

		// Read the options (2 bytes)
		final int opts = NB.decodeUInt16(scratch, 6);
		if ((opts & OPT_FULL) == 0)
			throw new IOException(MessageFormat.format(
					JGitText.get().expectedGot, Integer.valueOf(OPT_FULL),
					Integer.valueOf(opts)));

		// Read the number of entries (1 int32)
		long numEntries = NB.decodeUInt32(scratch, 8);
		if (numEntries > Integer.MAX_VALUE)
			throw new IOException(JGitText.get().indexFileIsTooLargeForJgit);

		// Checksum applied on the bottom of the corresponding pack file.
		this.packChecksum = new byte[20];
		System.arraycopy(scratch, 12, packChecksum, 0, packChecksum.length);

		// Read the bitmaps for the Git types
		SimpleDataInput dataInput = new SimpleDataInput(fd);
		this.commits = readBitmap(dataInput);
		this.trees = readBitmap(dataInput);
		this.blobs = readBitmap(dataInput);
		this.tags = readBitmap(dataInput);

		// An entry is object id, xor offset, flag byte, and a length encoded
		// bitmap. The object id is an int32 of the nth position sorted by name.
		// The xor offset is a single byte offset back in the list of entries.
		StoredBitmap[] recentBitmaps = new StoredBitmap[MAX_XOR_OFFSET];
		for (int i = 0; i < (int) numEntries; i++) {
			IO.readFully(fd, scratch, 0, 6);
			int nthObjectId = NB.decodeInt32(scratch, 0);
			int xorOffset = scratch[4];
			int flags = scratch[5];
			EWAHCompressedBitmap bitmap = readBitmap(dataInput);

			if (nthObjectId < 0)
				throw new IOException(MessageFormat.format(
						JGitText.get().invalidId, String.valueOf(nthObjectId)));
			if (xorOffset < 0)
				throw new IOException(MessageFormat.format(
						JGitText.get().invalidId, String.valueOf(xorOffset)));
			if (xorOffset > MAX_XOR_OFFSET)
				throw new IOException(MessageFormat.format(
						JGitText.get().expectedLessThanGot,
						String.valueOf(MAX_XOR_OFFSET),
						String.valueOf(xorOffset)));
			if (xorOffset > i)
				throw new IOException(MessageFormat.format(
						JGitText.get().expectedLessThanGot, String.valueOf(i),
						String.valueOf(xorOffset)));

			ObjectId objectId = packIndex.getObjectId(nthObjectId);
			StoredBitmap xorBitmap = null;
			if (xorOffset > 0) {
				int index = (i - xorOffset);
				xorBitmap = recentBitmaps[index % recentBitmaps.length];
				if (xorBitmap == null)
					throw new IOException(MessageFormat.format(
							JGitText.get().invalidId,
							String.valueOf(xorOffset)));
			}

			StoredBitmap sb = new StoredBitmap(
					objectId, bitmap, xorBitmap, flags);
			bitmaps.add(sb);
			recentBitmaps[i % recentBitmaps.length] = sb;
		}
	}

	/** {@inheritDoc} */
	@Override
	public int findPosition(AnyObjectId objectId) {
		long offset = packIndex.findOffset(objectId);
		if (offset == -1)
			return -1;
		return reverseIndex.findPostion(offset);
	}

	/** {@inheritDoc} */
	@Override
	public ObjectId getObject(int position) throws IllegalArgumentException {
		ObjectId objectId = reverseIndex.findObjectByPosition(position);
		if (objectId == null)
			throw new IllegalArgumentException();
		return objectId;
	}

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

	/** {@inheritDoc} */
	@Override
	public EWAHCompressedBitmap ofObjectType(
			EWAHCompressedBitmap bitmap, int type) {
		switch (type) {
		case Constants.OBJ_BLOB:
			return blobs.and(bitmap);
		case Constants.OBJ_TREE:
			return trees.and(bitmap);
		case Constants.OBJ_COMMIT:
			return commits.and(bitmap);
		case Constants.OBJ_TAG:
			return tags.and(bitmap);
		}
		throw new IllegalArgumentException();
	}

	/** {@inheritDoc} */
	@Override
	public int getBitmapCount() {
		return bitmaps.size();
	}

	/** {@inheritDoc} */
	@Override
	public boolean equals(Object o) {
		// TODO(cranger): compare the pack checksum?
		if (o instanceof PackBitmapIndexV1)
			return getPackIndex() == ((PackBitmapIndexV1) o).getPackIndex();
		return false;
	}

	/** {@inheritDoc} */
	@Override
	public int hashCode() {
		return getPackIndex().hashCode();
	}

	PackIndex getPackIndex() {
		return packIndex;
	}

	private static EWAHCompressedBitmap readBitmap(DataInput dataInput)
			throws IOException {
		EWAHCompressedBitmap bitmap = new EWAHCompressedBitmap();
		bitmap.deserialize(dataInput);
		return bitmap;
	}
}