/*
 * Copyright (C) 2008-2009, Google Inc.
 * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com> 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.pack;

import static org.eclipse.jgit.lib.Constants.OBJ_OFS_DELTA;
import static org.eclipse.jgit.lib.Constants.OBJ_REF_DELTA;
import static org.eclipse.jgit.lib.Constants.PACK_SIGNATURE;

import java.io.IOException;
import java.io.OutputStream;

import org.eclipse.jgit.internal.storage.io.CancellableDigestOutputStream;
import org.eclipse.jgit.lib.ProgressMonitor;
import org.eclipse.jgit.util.NB;

/**
 * Custom output stream to support
 * {@link org.eclipse.jgit.internal.storage.pack.PackWriter}.
 */
public final class PackOutputStream extends CancellableDigestOutputStream {

	private final PackWriter packWriter;

	private final byte[] headerBuffer = new byte[32];

	private final byte[] copyBuffer = new byte[64 << 10];

	private boolean ofsDelta;

	/**
	 * Initialize a pack output stream.
	 * <p>
	 * This constructor is exposed to support debugging the JGit library only.
	 * Application or storage level code should not create a PackOutputStream,
	 * instead use {@link org.eclipse.jgit.internal.storage.pack.PackWriter},
	 * and let the writer create the stream.
	 *
	 * @param writeMonitor
	 *            monitor to update on object output progress.
	 * @param out
	 *            target stream to receive all object contents.
	 * @param pw
	 *            packer that is going to perform the output.
	 */
	public PackOutputStream(final ProgressMonitor writeMonitor,
			final OutputStream out, final PackWriter pw) {
		super(writeMonitor, out);
		this.packWriter = pw;
	}

	final void writeFileHeader(int version, long objectCount)
			throws IOException {
		System.arraycopy(PACK_SIGNATURE, 0, headerBuffer, 0, 4);
		NB.encodeInt32(headerBuffer, 4, version);
		NB.encodeInt32(headerBuffer, 8, (int) objectCount);
		write(headerBuffer, 0, 12);
		ofsDelta = packWriter.isDeltaBaseAsOffset();
	}

	/**
	 * Write one object.
	 *
	 * If the object was already written, this method does nothing and returns
	 * quickly. This case occurs whenever an object was written out of order in
	 * order to ensure the delta base occurred before the object that needs it.
	 *
	 * @param otp
	 *            the object to write.
	 * @throws java.io.IOException
	 *             the object cannot be read from the object reader, or the
	 *             output stream is no longer accepting output. Caller must
	 *             examine the type of exception and possibly its message to
	 *             distinguish between these cases.
	 */
	public final void writeObject(ObjectToPack otp) throws IOException {
		packWriter.writeObject(this, otp);
	}

	/**
	 * Commits the object header onto the stream.
	 * <p>
	 * Once the header has been written, the object representation must be fully
	 * output, or packing must abort abnormally.
	 *
	 * @param otp
	 *            the object to pack. Header information is obtained.
	 * @param rawLength
	 *            number of bytes of the inflated content. For an object that is
	 *            in whole object format, this is the same as the object size.
	 *            For an object that is in a delta format, this is the size of
	 *            the inflated delta instruction stream.
	 * @throws java.io.IOException
	 *             the underlying stream refused to accept the header.
	 */
	@SuppressWarnings("ShortCircuitBoolean")
	public final void writeHeader(ObjectToPack otp, long rawLength)
			throws IOException {
		ObjectToPack b = otp.getDeltaBase();
		if (b != null && (b.isWritten() & ofsDelta)) { // Non-short-circuit logic is intentional
			int n = objectHeader(rawLength, OBJ_OFS_DELTA, headerBuffer);
			n = ofsDelta(length() - b.getOffset(), headerBuffer, n);
			write(headerBuffer, 0, n);
		} else if (otp.isDeltaRepresentation()) {
			int n = objectHeader(rawLength, OBJ_REF_DELTA, headerBuffer);
			otp.getDeltaBaseId().copyRawTo(headerBuffer, n);
			write(headerBuffer, 0, n + 20);
		} else {
			int n = objectHeader(rawLength, otp.getType(), headerBuffer);
			write(headerBuffer, 0, n);
		}
	}

	private static final int objectHeader(long len, int type, byte[] buf) {
		byte b = (byte) ((type << 4) | (len & 0x0F));
		int n = 0;
		for (len >>>= 4; len != 0; len >>>= 7) {
			buf[n++] = (byte) (0x80 | b);
			b = (byte) (len & 0x7F);
		}
		buf[n++] = b;
		return n;
	}

	private static final int ofsDelta(long diff, byte[] buf, int p) {
		p += ofsDeltaVarIntLength(diff);
		int n = p;
		buf[--n] = (byte) (diff & 0x7F);
		while ((diff >>>= 7) != 0)
			buf[--n] = (byte) (0x80 | (--diff & 0x7F));
		return p;
	}

	private static final int ofsDeltaVarIntLength(long v) {
		int n = 1;
		for (; (v >>>= 7) != 0; n++)
			--v;
		return n;
	}

	/**
	 * Get a temporary buffer writers can use to copy data with.
	 *
	 * @return a temporary buffer writers can use to copy data with.
	 */
	public final byte[] getCopyBuffer() {
		return copyBuffer;
	}

	void endObject() {
		getWriteMonitor().update(1);
	}
}