/*
    * Copyright (C) 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
    * Copyright (C) 2006-2007, Shawn O. Pearce <spearce@spearce.org> 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 org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.util.QuotedString;
  import org.eclipse.jgit.util.RawParseUtils;
  
  /**
   * Recreate a stream from a base stream and a GIT pack delta.
   * <p>
   * This entire class is heavily cribbed from <code>patch-delta.c</code> in the
   * GIT project. The original delta patching code was written by Nicolas Pitre
   * (&lt;nico@cam.org&gt;).
   * </p>
   */
  public class BinaryDelta {
  	/**
  	 * Length of the base object in the delta stream.
  	 *
  	 * @param delta
  	 *            the delta stream, or at least the header of it.
  	 * @return the base object's size.
  	 */
  	public static long getBaseSize(byte[] delta) {
  		int p = 0;
  		long baseLen = 0;
  		int c, shift = 0;
  		do {
  			c = delta[p++] & 0xff;
  			baseLen |= ((long) (c & 0x7f)) << shift;
  			shift += 7;
  		} while ((c & 0x80) != 0);
  		return baseLen;
  	}
  
  	/**
  	 * Length of the resulting object in the delta stream.
  	 *
  	 * @param delta
  	 *            the delta stream, or at least the header of it.
  	 * @return the resulting object's size.
  	 */
  	public static long getResultSize(byte[] delta) {
  		int p = 0;
  
  		// Skip length of the base object.
  		//
  		int c;
  		do {
  			c = delta[p++] & 0xff;
  		} while ((c & 0x80) != 0);
  
  		long resLen = 0;
  		int shift = 0;
  		do {
  			c = delta[p++] & 0xff;
  			resLen |= ((long) (c & 0x7f)) << shift;
  			shift += 7;
  		} while ((c & 0x80) != 0);
  		return resLen;
  	}
  
  	/**
  	 * Apply the changes defined by delta to the data in base, yielding a new
  	 * array of bytes.
  	 *
  	 * @param base
  	 *            some byte representing an object of some kind.
  	 * @param delta
  	 *            a git pack delta defining the transform from one version to
  	 *            another.
  	 * @return patched base
  	 */
  	public static final byte[] apply(byte[] base, byte[] delta) {
  		return apply(base, delta, null);
  	}
  
  	/**
  	 * Apply the changes defined by delta to the data in base, yielding a new
  	 * array of bytes.
  	 *
  	 * @param base
  	 *            some byte representing an object of some kind.
  	 * @param delta
  	 *            a git pack delta defining the transform from one version to
  	 *            another.
  	 * @param result
  	 *            array to store the result into. If null the result will be
  	 *            allocated and returned.
 	 * @return either {@code result}, or the result array allocated.
 	 */
 	public static final byte[] apply(final byte[] base, final byte[] delta,
 			byte[] result) {
 		int deltaPtr = 0;
 
 		// Length of the base object (a variable length int).
 		//
 		int baseLen = 0;
 		int c, shift = 0;
 		do {
 			c = delta[deltaPtr++] & 0xff;
 			baseLen |= (c & 0x7f) << shift;
 			shift += 7;
 		} while ((c & 0x80) != 0);
 		if (base.length != baseLen)
 			throw new IllegalArgumentException(
 					JGitText.get().baseLengthIncorrect);
 
 		// Length of the resulting object (a variable length int).
 		//
 		int resLen = 0;
 		shift = 0;
 		do {
 			c = delta[deltaPtr++] & 0xff;
 			resLen |= (c & 0x7f) << shift;
 			shift += 7;
 		} while ((c & 0x80) != 0);
 
 		if (result == null)
 			result = new byte[resLen];
 		else if (result.length != resLen)
 			throw new IllegalArgumentException(
 					JGitText.get().resultLengthIncorrect);
 
 		int resultPtr = 0;
 		while (deltaPtr < delta.length) {
 			final int cmd = delta[deltaPtr++] & 0xff;
 			if ((cmd & 0x80) != 0) {
 				// Determine the segment of the base which should
 				// be copied into the output. The segment is given
 				// as an offset and a length.
 				//
 				int copyOffset = 0;
 				if ((cmd & 0x01) != 0)
 					copyOffset = delta[deltaPtr++] & 0xff;
 				if ((cmd & 0x02) != 0)
 					copyOffset |= (delta[deltaPtr++] & 0xff) << 8;
 				if ((cmd & 0x04) != 0)
 					copyOffset |= (delta[deltaPtr++] & 0xff) << 16;
 				if ((cmd & 0x08) != 0)
 					copyOffset |= (delta[deltaPtr++] & 0xff) << 24;
 
 				int copySize = 0;
 				if ((cmd & 0x10) != 0)
 					copySize = delta[deltaPtr++] & 0xff;
 				if ((cmd & 0x20) != 0)
 					copySize |= (delta[deltaPtr++] & 0xff) << 8;
 				if ((cmd & 0x40) != 0)
 					copySize |= (delta[deltaPtr++] & 0xff) << 16;
 				if (copySize == 0)
 					copySize = 0x10000;
 
 				System.arraycopy(base, copyOffset, result, resultPtr, copySize);
 				resultPtr += copySize;
 			} else if (cmd != 0) {
 				// Anything else the data is literal within the delta
 				// itself.
 				//
 				System.arraycopy(delta, deltaPtr, result, resultPtr, cmd);
 				deltaPtr += cmd;
 				resultPtr += cmd;
 			} else {
 				// cmd == 0 has been reserved for future encoding but
 				// for now its not acceptable.
 				//
 				throw new IllegalArgumentException(
 						JGitText.get().unsupportedCommand0);
 			}
 		}
 
 		return result;
 	}
 
 	/**
 	 * Format this delta as a human readable string.
 	 *
 	 * @param delta
 	 *            the delta instruction sequence to format.
 	 * @return the formatted delta.
 	 */
 	public static String format(byte[] delta) {
 		return format(delta, true);
 	}
 
 	/**
 	 * Format this delta as a human readable string.
 	 *
 	 * @param delta
 	 *            the delta instruction sequence to format.
 	 * @param includeHeader
 	 *            true if the header (base size and result size) should be
 	 *            included in the formatting.
 	 * @return the formatted delta.
 	 */
 	public static String format(byte[] delta, boolean includeHeader) {
 		StringBuilder r = new StringBuilder();
 		int deltaPtr = 0;
 
 		long baseLen = 0;
 		int c, shift = 0;
 		do {
 			c = delta[deltaPtr++] & 0xff;
 			baseLen |= ((long) (c & 0x7f)) << shift;
 			shift += 7;
 		} while ((c & 0x80) != 0);
 
 		long resLen = 0;
 		shift = 0;
 		do {
 			c = delta[deltaPtr++] & 0xff;
 			resLen |= ((long) (c & 0x7f)) << shift;
 			shift += 7;
 		} while ((c & 0x80) != 0);
 
 		if (includeHeader) {
 			r.append("DELTA( BASE="); //$NON-NLS-1$
 			r.append(baseLen);
 			r.append(" RESULT="); //$NON-NLS-1$
 			r.append(resLen);
 			r.append(" )\n"); //$NON-NLS-1$
 		}
 
 		while (deltaPtr < delta.length) {
 			final int cmd = delta[deltaPtr++] & 0xff;
 			if ((cmd & 0x80) != 0) {
 				// Determine the segment of the base which should
 				// be copied into the output. The segment is given
 				// as an offset and a length.
 				//
 				int copyOffset = 0;
 				if ((cmd & 0x01) != 0)
 					copyOffset = delta[deltaPtr++] & 0xff;
 				if ((cmd & 0x02) != 0)
 					copyOffset |= (delta[deltaPtr++] & 0xff) << 8;
 				if ((cmd & 0x04) != 0)
 					copyOffset |= (delta[deltaPtr++] & 0xff) << 16;
 				if ((cmd & 0x08) != 0)
 					copyOffset |= (delta[deltaPtr++] & 0xff) << 24;
 
 				int copySize = 0;
 				if ((cmd & 0x10) != 0)
 					copySize = delta[deltaPtr++] & 0xff;
 				if ((cmd & 0x20) != 0)
 					copySize |= (delta[deltaPtr++] & 0xff) << 8;
 				if ((cmd & 0x40) != 0)
 					copySize |= (delta[deltaPtr++] & 0xff) << 16;
 				if (copySize == 0)
 					copySize = 0x10000;
 
 				r.append("  COPY  ("); //$NON-NLS-1$
 				r.append(copyOffset);
 				r.append(", "); //$NON-NLS-1$
 				r.append(copySize);
 				r.append(")\n"); //$NON-NLS-1$
 			} else if (cmd != 0) {
 				// Anything else the data is literal within the delta
 				// itself.
 				//
 				r.append("  INSERT("); //$NON-NLS-1$
 				r.append(QuotedString.GIT_PATH.quote(RawParseUtils.decode(
 						delta, deltaPtr, deltaPtr + cmd)));
 				r.append(")\n"); //$NON-NLS-1$
 				deltaPtr += cmd;
 			} else {
 				// cmd == 0 has been reserved for future encoding but
 				// for now its not acceptable.
 				//
 				throw new IllegalArgumentException(
 						JGitText.get().unsupportedCommand0);
 			}
 		}
 
 		return r.toString();
 	}
 }