/*
    * Copyright (C) 2008-2010, Google Inc.
    * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
    * and other copyright owners as documented in the project's IP log.
    *
    * This program and the accompanying materials are made available
    * under the terms of the Eclipse Distribution License v1.0 which
    * accompanies this distribution, is reproduced below, and is
    * available at http://www.eclipse.org/org/documents/edl-v10.php
   *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or
   * without modification, are permitted provided that the following
   * conditions are met:
   *
   * - Redistributions of source code must retain the above copyright
   *   notice, this list of conditions and the following disclaimer.
   *
   * - Redistributions in binary form must reproduce the above
   *   copyright notice, this list of conditions and the following
   *   disclaimer in the documentation and/or other materials provided
   *   with the distribution.
   *
   * - Neither the name of the Eclipse Foundation, Inc. nor the
   *   names of its contributors may be used to endorse or promote
   *   products derived from this software without specific prior
   *   written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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  package org.eclipse.jgit.treewalk;
  
  import java.io.IOException;
  import java.util.Arrays;
  
  import org.eclipse.jgit.errors.IncorrectObjectTypeException;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.lib.AnyObjectId;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.FileMode;
  import org.eclipse.jgit.lib.MutableObjectId;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectReader;
  
  /** Parses raw Git trees from the canonical semi-text/semi-binary format. */
  public class CanonicalTreeParser extends AbstractTreeIterator {
  	private static final byte[] EMPTY = {};
  
  	private byte[] raw;
  
  	/** First offset within {@link #raw} of the prior entry. */
  	private int prevPtr;
  
  	/** First offset within {@link #raw} of the current entry's data. */
  	private int currPtr;
  
  	/** Offset one past the current entry (first byte of next entry). */
  	private int nextPtr;
  
  	/** Create a new parser. */
  	public CanonicalTreeParser() {
  		reset(EMPTY);
  	}
  
  	/**
  	 * Create a new parser for a tree appearing in a subset of a repository.
  	 *
  	 * @param prefix
  	 *            position of this iterator in the repository tree. The value
  	 *            may be null or the empty array to indicate the prefix is the
  	 *            root of the repository. A trailing slash ('/') is
  	 *            automatically appended if the prefix does not end in '/'.
  	 * @param reader
  	 *            reader to load the tree data from.
  	 * @param treeId
  	 *            identity of the tree being parsed; used only in exception
  	 *            messages if data corruption is found.
  	 * @throws MissingObjectException
  	 *             the object supplied is not available from the repository.
  	 * @throws IncorrectObjectTypeException
  	 *             the object supplied as an argument is not actually a tree and
  	 *             cannot be parsed as though it were a tree.
  	 * @throws IOException
  	 *             a loose object or pack file could not be read.
  	 */
 	public CanonicalTreeParser(final byte[] prefix, final ObjectReader reader,
 			final AnyObjectId treeId) throws IncorrectObjectTypeException,
 			IOException {
 		super(prefix);
 		reset(reader, treeId);
 	}
 
 	private CanonicalTreeParser(final CanonicalTreeParser p) {
 		super(p);
 	}
 
 	/**
 	 * @return the parent of this tree parser
 	 * @deprecated internal use only
 	 */
 	@Deprecated
 	public CanonicalTreeParser getParent() {
 		return (CanonicalTreeParser) parent;
 	}
 
 	/**
 	 * Reset this parser to walk through the given tree data.
 	 *
 	 * @param treeData
 	 *            the raw tree content.
 	 */
 	public void reset(final byte[] treeData) {
 		raw = treeData;
 		prevPtr = -1;
 		currPtr = 0;
 		if (eof())
 			nextPtr = 0;
 		else
 			parseEntry();
 	}
 
 	/**
 	 * Reset this parser to walk through the given tree.
 	 *
 	 * @param reader
 	 *            reader to use during repository access.
 	 * @param id
 	 *            identity of the tree being parsed; used only in exception
 	 *            messages if data corruption is found.
 	 * @return the root level parser.
 	 * @throws MissingObjectException
 	 *             the object supplied is not available from the repository.
 	 * @throws IncorrectObjectTypeException
 	 *             the object supplied as an argument is not actually a tree and
 	 *             cannot be parsed as though it were a tree.
 	 * @throws IOException
 	 *             a loose object or pack file could not be read.
 	 */
 	public CanonicalTreeParser resetRoot(final ObjectReader reader,
 			final AnyObjectId id) throws IncorrectObjectTypeException,
 			IOException {
 		CanonicalTreeParser p = this;
 		while (p.parent != null)
 			p = (CanonicalTreeParser) p.parent;
 		p.reset(reader, id);
 		return p;
 	}
 
 	/** @return this iterator, or its parent, if the tree is at eof. */
 	public CanonicalTreeParser next() {
 		CanonicalTreeParser p = this;
 		for (;;) {
 			if (p.nextPtr == p.raw.length) {
 				// This parser has reached EOF, return to the parent.
 				if (p.parent == null) {
 					p.currPtr = p.nextPtr;
 					return p;
 				}
 				p = (CanonicalTreeParser) p.parent;
 				continue;
 			}
 
 			p.prevPtr = p.currPtr;
 			p.currPtr = p.nextPtr;
 			p.parseEntry();
 			return p;
 		}
 	}
 
 	/**
 	 * Reset this parser to walk through the given tree.
 	 *
 	 * @param reader
 	 *            reader to use during repository access.
 	 * @param id
 	 *            identity of the tree being parsed; used only in exception
 	 *            messages if data corruption is found.
 	 * @throws MissingObjectException
 	 *             the object supplied is not available from the repository.
 	 * @throws IncorrectObjectTypeException
 	 *             the object supplied as an argument is not actually a tree and
 	 *             cannot be parsed as though it were a tree.
 	 * @throws IOException
 	 *             a loose object or pack file could not be read.
 	 */
 	public void reset(final ObjectReader reader, final AnyObjectId id)
 			throws IncorrectObjectTypeException, IOException {
 		reset(reader.open(id, Constants.OBJ_TREE).getCachedBytes());
 	}
 
 	@Override
 	public CanonicalTreeParser createSubtreeIterator(final ObjectReader reader,
 			final MutableObjectId idBuffer)
 			throws IncorrectObjectTypeException, IOException {
 		idBuffer.fromRaw(idBuffer(), idOffset());
 		if (!FileMode.TREE.equals(mode)) {
 			final ObjectId me = idBuffer.toObjectId();
 			throw new IncorrectObjectTypeException(me, Constants.TYPE_TREE);
 		}
 		return createSubtreeIterator0(reader, idBuffer);
 	}
 
 	/**
 	 * Back door to quickly create a subtree iterator for any subtree.
 	 * <p>
 	 * Don't use this unless you are ObjectWalk. The method is meant to be
 	 * called only once the current entry has been identified as a tree and its
 	 * identity has been converted into an ObjectId.
 	 *
 	 * @param reader
 	 *            reader to load the tree data from.
 	 * @param id
 	 *            ObjectId of the tree to open.
 	 * @return a new parser that walks over the current subtree.
 	 * @throws IOException
 	 *             a loose object or pack file could not be read.
 	 */
 	public final CanonicalTreeParser createSubtreeIterator0(
 			final ObjectReader reader, final AnyObjectId id)
 			throws IOException {
 		final CanonicalTreeParser p = new CanonicalTreeParser(this);
 		p.reset(reader, id);
 		return p;
 	}
 
 	public CanonicalTreeParser createSubtreeIterator(final ObjectReader reader)
 			throws IncorrectObjectTypeException, IOException {
 		return createSubtreeIterator(reader, new MutableObjectId());
 	}
 
 	@Override
 	public boolean hasId() {
 		return true;
 	}
 
 	@Override
 	public byte[] idBuffer() {
 		return raw;
 	}
 
 	@Override
 	public int idOffset() {
 		return nextPtr - Constants.OBJECT_ID_LENGTH;
 	}
 
 	@Override
 	public void reset() {
 		if (!first())
 			reset(raw);
 	}
 
 	@Override
 	public boolean first() {
 		return currPtr == 0;
 	}
 
 	public boolean eof() {
 		return currPtr == raw.length;
 	}
 
 	@Override
 	public void next(int delta) {
 		if (delta == 1) {
 			// Moving forward one is the most common case.
 			//
 			prevPtr = currPtr;
 			currPtr = nextPtr;
 			if (!eof())
 				parseEntry();
 			return;
 		}
 
 		// Fast skip over records, then parse the last one.
 		//
 		final int end = raw.length;
 		int ptr = nextPtr;
 		while (--delta > 0 && ptr != end) {
 			prevPtr = ptr;
 			while (raw[ptr] != 0)
 				ptr++;
 			ptr += Constants.OBJECT_ID_LENGTH + 1;
 		}
 		if (delta != 0)
 			throw new ArrayIndexOutOfBoundsException(delta);
 		currPtr = ptr;
 		if (!eof())
 			parseEntry();
 	}
 
 	@Override
 	public void back(int delta) {
 		if (delta == 1 && 0 <= prevPtr) {
 			// Moving back one is common in NameTreeWalk, as the average tree
 			// won't have D/F type conflicts to study.
 			//
 			currPtr = prevPtr;
 			prevPtr = -1;
 			if (!eof())
 				parseEntry();
 			return;
 		} else if (delta <= 0)
 			throw new ArrayIndexOutOfBoundsException(delta);
 
 		// Fast skip through the records, from the beginning of the tree.
 		// There is no reliable way to read the tree backwards, so we must
 		// parse all over again from the beginning. We hold the last "delta"
 		// positions in a buffer, so we can find the correct position later.
 		//
 		final int[] trace = new int[delta + 1];
 		Arrays.fill(trace, -1);
 		int ptr = 0;
 		while (ptr != currPtr) {
 			System.arraycopy(trace, 1, trace, 0, delta);
 			trace[delta] = ptr;
 			while (raw[ptr] != 0)
 				ptr++;
 			ptr += Constants.OBJECT_ID_LENGTH + 1;
 		}
 		if (trace[1] == -1)
 			throw new ArrayIndexOutOfBoundsException(delta);
 		prevPtr = trace[0];
 		currPtr = trace[1];
 		parseEntry();
 	}
 
 	private void parseEntry() {
 		int ptr = currPtr;
 		byte c = raw[ptr++];
 		int tmp = c - '0';
 		for (;;) {
 			c = raw[ptr++];
 			if (' ' == c)
 				break;
 			tmp <<= 3;
 			tmp += c - '0';
 		}
 		mode = tmp;
 
 		tmp = pathOffset;
 		for (;; tmp++) {
 			c = raw[ptr++];
 			if (c == 0)
 				break;
 			try {
 				path[tmp] = c;
 			} catch (ArrayIndexOutOfBoundsException e) {
 				growPath(tmp);
 				path[tmp] = c;
 			}
 		}
 		pathLen = tmp;
 		nextPtr = ptr + Constants.OBJECT_ID_LENGTH;
 	}
 }