/*
    * Copyright (C) 2008-2009, Google Inc.
    * Copyright (C) 2008, 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.dircache;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.util.Collections;
  
  import org.eclipse.jgit.attributes.AttributesNode;
  import org.eclipse.jgit.attributes.AttributesRule;
  import org.eclipse.jgit.errors.IncorrectObjectTypeException;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.FileMode;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectLoader;
  import org.eclipse.jgit.lib.ObjectReader;
  import org.eclipse.jgit.treewalk.AbstractTreeIterator;
  import org.eclipse.jgit.treewalk.EmptyTreeIterator;
  import org.eclipse.jgit.util.RawParseUtils;
  
  /**
   * Iterate a {@link org.eclipse.jgit.dircache.DirCache} as part of a
   * <code>TreeWalk</code>.
   * <p>
   * This is an iterator to adapt a loaded <code>DirCache</code> instance (such as
   * read from an existing <code>.git/index</code> file) to the tree structure
   * used by a <code>TreeWalk</code>, making it possible for applications to walk
   * over any combination of tree objects already in the object database, index
   * files, or working directories.
   *
   * @see org.eclipse.jgit.treewalk.TreeWalk
   */
  public class DirCacheIterator extends AbstractTreeIterator {
  	/** Byte array holding ".gitattributes" string */
  	private static final byte[] DOT_GIT_ATTRIBUTES_BYTES = Constants.DOT_GIT_ATTRIBUTES
  			.getBytes(UTF_8);
  
  	/** The cache this iterator was created to walk. */
  	protected final DirCache cache;
  
  	/** The tree this iterator is walking. */
  	private final DirCacheTree tree;
  
  	/** First position in this tree. */
  	private final int treeStart;
  
  	/** Last position in this tree. */
  	private final int treeEnd;
  
  	/** Special buffer to hold the ObjectId of {@link #currentSubtree}. */
  	private final byte[] subtreeId;
  
  	/** Index of entry within {@link #cache}. */
  	protected int ptr;
  
  	/** Next subtree to consider within {@link #tree}. */
  	private int nextSubtreePos;
  
  	/** The current file entry from {@link #cache}. */
  	protected DirCacheEntry currentEntry;
  
  	/** The subtree containing {@link #currentEntry} if this is first entry. */
  	protected DirCacheTree currentSubtree;
  
  	/**
  	 * Create a new iterator for an already loaded DirCache instance.
  	 * <p>
  	 * The iterator implementation may copy part of the cache's data during
  	 * construction, so the cache must be read in prior to creating the
  	 * iterator.
  	 *
  	 * @param dc
  	 *            the cache to walk. It must be already loaded into memory.
  	 */
  	public DirCacheIterator(DirCache dc) {
  		cache = dc;
  		tree = dc.getCacheTree(true);
  		treeStart = 0;
  		treeEnd = tree.getEntrySpan();
  		subtreeId = new byte[Constants.OBJECT_ID_LENGTH];
  		if (!eof())
  			parseEntry();
  	}
  
  	DirCacheIterator(DirCacheIterator p, DirCacheTree dct) {
  		super(p, p.path, p.pathLen + 1);
  		cache = p.cache;
  		tree = dct;
 		treeStart = p.ptr;
 		treeEnd = treeStart + tree.getEntrySpan();
 		subtreeId = p.subtreeId;
 		ptr = p.ptr;
 		parseEntry();
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public AbstractTreeIterator createSubtreeIterator(ObjectReader reader)
 			throws IncorrectObjectTypeException, IOException {
 		if (currentSubtree == null)
 			throw new IncorrectObjectTypeException(getEntryObjectId(),
 					Constants.TYPE_TREE);
 		return new DirCacheIterator(this, currentSubtree);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public EmptyTreeIterator createEmptyTreeIterator() {
 		final byte[] n = new byte[Math.max(pathLen + 1, DEFAULT_PATH_SIZE)];
 		System.arraycopy(path, 0, n, 0, pathLen);
 		n[pathLen] = '/';
 		return new EmptyTreeIterator(this, n, pathLen + 1);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public boolean hasId() {
 		if (currentSubtree != null)
 			return currentSubtree.isValid();
 		return currentEntry != null;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public byte[] idBuffer() {
 		if (currentSubtree != null)
 			return currentSubtree.isValid() ? subtreeId : zeroid;
 		if (currentEntry != null)
 			return currentEntry.idBuffer();
 		return zeroid;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public int idOffset() {
 		if (currentSubtree != null)
 			return 0;
 		if (currentEntry != null)
 			return currentEntry.idOffset();
 		return 0;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void reset() {
 		if (!first()) {
 			ptr = treeStart;
 			nextSubtreePos = 0;
 			currentEntry = null;
 			currentSubtree = null;
 			if (!eof())
 				parseEntry();
 		}
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public boolean first() {
 		return ptr == treeStart;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public boolean eof() {
 		return ptr == treeEnd;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void next(int delta) {
 		while (--delta >= 0) {
 			if (currentSubtree != null)
 				ptr += currentSubtree.getEntrySpan();
 			else
 				ptr++;
 			if (eof())
 				break;
 			parseEntry();
 		}
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void back(int delta) {
 		while (--delta >= 0) {
 			if (currentSubtree != null)
 				nextSubtreePos--;
 			ptr--;
 			parseEntry(false);
 			if (currentSubtree != null)
 				ptr -= currentSubtree.getEntrySpan() - 1;
 		}
 	}
 
 	private void parseEntry() {
 		parseEntry(true);
 	}
 
 	private void parseEntry(boolean forward) {
 		currentEntry = cache.getEntry(ptr);
 		final byte[] cep = currentEntry.path;
 
 		if (!forward) {
 			if (nextSubtreePos > 0) {
 				final DirCacheTree p = tree.getChild(nextSubtreePos - 1);
 				if (p.contains(cep, pathOffset, cep.length)) {
 					nextSubtreePos--;
 					currentSubtree = p;
 				}
 			}
 		}
 		if (nextSubtreePos != tree.getChildCount()) {
 			final DirCacheTree s = tree.getChild(nextSubtreePos);
 			if (s.contains(cep, pathOffset, cep.length)) {
 				// The current position is the first file of this subtree.
 				// Use the subtree instead as the current position.
 				//
 				currentSubtree = s;
 				nextSubtreePos++;
 
 				if (s.isValid())
 					s.getObjectId().copyRawTo(subtreeId, 0);
 				mode = FileMode.TREE.getBits();
 				path = cep;
 				pathLen = pathOffset + s.nameLength();
 				return;
 			}
 		}
 
 		// The current position is a file/symlink/gitlink so we
 		// do not have a subtree located here.
 		//
 		mode = currentEntry.getRawMode();
 		path = cep;
 		pathLen = cep.length;
 		currentSubtree = null;
 		// Checks if this entry is a .gitattributes file
 		if (RawParseUtils.match(path, pathOffset, DOT_GIT_ATTRIBUTES_BYTES) == path.length)
 			attributesNode = new LazyLoadingAttributesNode(
 					currentEntry.getObjectId());
 	}
 
 	/**
 	 * Get the DirCacheEntry for the current file.
 	 *
 	 * @return the current cache entry, if this iterator is positioned on a
 	 *         non-tree.
 	 */
 	public DirCacheEntry getDirCacheEntry() {
 		return currentSubtree == null ? currentEntry : null;
 	}
 
 	/**
 	 * Retrieves the {@link org.eclipse.jgit.attributes.AttributesNode} for the
 	 * current entry.
 	 *
 	 * @param reader
 	 *            {@link org.eclipse.jgit.lib.ObjectReader} used to parse the
 	 *            .gitattributes entry.
 	 * @return {@link org.eclipse.jgit.attributes.AttributesNode} for the
 	 *         current entry.
 	 * @throws java.io.IOException
 	 * @since 3.7
 	 */
 	public AttributesNode getEntryAttributesNode(ObjectReader reader)
 			throws IOException {
 		if (attributesNode instanceof LazyLoadingAttributesNode)
 			attributesNode = ((LazyLoadingAttributesNode) attributesNode)
 					.load(reader);
 		return attributesNode;
 	}
 
 	/**
 	 * {@link AttributesNode} implementation that provides lazy loading
 	 * facilities.
 	 */
 	private static class LazyLoadingAttributesNode extends AttributesNode {
 		final ObjectId objectId;
 
 		LazyLoadingAttributesNode(ObjectId objectId) {
 			super(Collections.<AttributesRule> emptyList());
 			this.objectId = objectId;
 
 		}
 
 		AttributesNode load(ObjectReader reader) throws IOException {
 			AttributesNode r = new AttributesNode();
 			ObjectLoader loader = reader.open(objectId);
 			if (loader != null) {
 				try (InputStream in = loader.openStream()) {
 					r.parse(in);
 				}
 			}
 			return r.getRules().isEmpty() ? null : r;
 		}
 	}
 
 }