/*
    * 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 static org.eclipse.jgit.lib.FileMode.TREE;
  import static org.eclipse.jgit.lib.TreeFormatter.entrySize;
  
  import java.io.IOException;
  import java.io.OutputStream;
  import java.nio.ByteBuffer;
  import java.util.Arrays;
  import java.util.Comparator;
  
  import org.eclipse.jgit.errors.UnmergedPathException;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectInserter;
  import org.eclipse.jgit.lib.TreeFormatter;
  import org.eclipse.jgit.util.MutableInteger;
  import org.eclipse.jgit.util.RawParseUtils;
  
  /**
   * Single tree record from the 'TREE' {@link org.eclipse.jgit.dircache.DirCache}
   * extension.
   * <p>
   * A valid cache tree record contains the object id of a tree object and the
   * total number of {@link org.eclipse.jgit.dircache.DirCacheEntry} instances
   * (counted recursively) from the DirCache contained within the tree. This
   * information facilitates faster traversal of the index and quicker generation
   * of tree objects prior to creating a new commit.
   * <p>
   * An invalid cache tree record indicates a known subtree whose file entries
   * have changed in ways that cause the tree to no longer have a known object id.
   * Invalid cache tree records must be revalidated prior to use.
   */
  public class DirCacheTree {
  	private static final byte[] NO_NAME = {};
  
  	private static final DirCacheTree[] NO_CHILDREN = {};
  
  	private static final Comparator<DirCacheTree> TREE_CMP = (DirCacheTree o1,
  			DirCacheTree o2) -> {
  		final byte[] a = o1.encodedName;
  		final byte[] b = o2.encodedName;
  		final int aLen = a.length;
  		final int bLen = b.length;
  		int cPos;
  		for (cPos = 0; cPos < aLen && cPos < bLen; cPos++) {
  			final int cmp = (a[cPos] & 0xff) - (b[cPos] & 0xff);
  			if (cmp != 0) {
  				return cmp;
  			}
  		}
  		if (aLen == bLen) {
  			return 0;
  		}
  		if (aLen < bLen) {
  			return '/' - (b[cPos] & 0xff);
  		}
  		return (a[cPos] & 0xff) - '/';
  	};
  
  	/** Tree this tree resides in; null if we are the root. */
  	private DirCacheTree parent;
  
  	/** Name of this tree within its parent. */
  	byte[] encodedName;
  
  	/** Number of {@link DirCacheEntry} records that belong to this tree. */
  	private int entrySpan;
  
  	/** Unique SHA-1 of this tree; null if invalid. */
  	private ObjectId id;
  
  	/** Child trees, if any, sorted by {@link #encodedName}. */
  	private DirCacheTree[] children;
  
  	/** Number of valid children in {@link #children}. */
  	private int childCnt;
  
  	DirCacheTree() {
  		encodedName = NO_NAME;
  		children = NO_CHILDREN;
  		childCnt = 0;
  		entrySpan = -1;
  	}
  
  	private DirCacheTree(final DirCacheTree myParent, final byte[] path,
  			final int pathOff, final int pathLen) {
 		parent = myParent;
 		encodedName = new byte[pathLen];
 		System.arraycopy(path, pathOff, encodedName, 0, pathLen);
 		children = NO_CHILDREN;
 		childCnt = 0;
 		entrySpan = -1;
 	}
 
 	DirCacheTree(final byte[] in, final MutableInteger off,
 			final DirCacheTree myParent) {
 		parent = myParent;
 
 		int ptr = RawParseUtils.next(in, off.value, '\0');
 		final int nameLen = ptr - off.value - 1;
 		if (nameLen > 0) {
 			encodedName = new byte[nameLen];
 			System.arraycopy(in, off.value, encodedName, 0, nameLen);
 		} else
 			encodedName = NO_NAME;
 
 		entrySpan = RawParseUtils.parseBase10(in, ptr, off);
 		final int subcnt = RawParseUtils.parseBase10(in, off.value, off);
 		off.value = RawParseUtils.next(in, off.value, '\n');
 
 		if (entrySpan >= 0) {
 			// Valid trees have a positive entry count and an id of a
 			// tree object that should exist in the object database.
 			//
 			id = ObjectId.fromRaw(in, off.value);
 			off.value += Constants.OBJECT_ID_LENGTH;
 		}
 
 		if (subcnt > 0) {
 			boolean alreadySorted = true;
 			children = new DirCacheTree[subcnt];
 			for (int i = 0; i < subcnt; i++) {
 				children[i] = new DirCacheTree(in, off, this);
 
 				// C Git's ordering differs from our own; it prefers to
 				// sort by length first. This sometimes produces a sort
 				// we do not desire. On the other hand it may have been
 				// created by us, and be sorted the way we want.
 				//
 				if (alreadySorted && i > 0
 						&& TREE_CMP.compare(children[i - 1], children[i]) > 0)
 					alreadySorted = false;
 			}
 			if (!alreadySorted)
 				Arrays.sort(children, 0, subcnt, TREE_CMP);
 		} else {
 			// Leaf level trees have no children, only (file) entries.
 			//
 			children = NO_CHILDREN;
 		}
 		childCnt = subcnt;
 	}
 
 	void write(byte[] tmp, OutputStream os) throws IOException {
 		int ptr = tmp.length;
 		tmp[--ptr] = '\n';
 		ptr = RawParseUtils.formatBase10(tmp, ptr, childCnt);
 		tmp[--ptr] = ' ';
 		ptr = RawParseUtils.formatBase10(tmp, ptr, isValid() ? entrySpan : -1);
 		tmp[--ptr] = 0;
 
 		os.write(encodedName);
 		os.write(tmp, ptr, tmp.length - ptr);
 		if (isValid()) {
 			id.copyRawTo(tmp, 0);
 			os.write(tmp, 0, Constants.OBJECT_ID_LENGTH);
 		}
 		for (int i = 0; i < childCnt; i++)
 			children[i].write(tmp, os);
 	}
 
 	/**
 	 * Determine if this cache is currently valid.
 	 * <p>
 	 * A valid cache tree knows how many
 	 * {@link org.eclipse.jgit.dircache.DirCacheEntry} instances from the parent
 	 * {@link org.eclipse.jgit.dircache.DirCache} reside within this tree
 	 * (recursively enumerated). It also knows the object id of the tree, as the
 	 * tree should be readily available from the repository's object database.
 	 *
 	 * @return true if this tree is knows key details about itself; false if the
 	 *         tree needs to be regenerated.
 	 */
 	public boolean isValid() {
 		return id != null;
 	}
 
 	/**
 	 * Get the number of entries this tree spans within the DirCache.
 	 * <p>
 	 * If this tree is not valid (see {@link #isValid()}) this method's return
 	 * value is always strictly negative (less than 0) but is otherwise an
 	 * undefined result.
 	 *
 	 * @return total number of entries (recursively) contained within this tree.
 	 */
 	public int getEntrySpan() {
 		return entrySpan;
 	}
 
 	/**
 	 * Get the number of cached subtrees contained within this tree.
 	 *
 	 * @return number of child trees available through this tree.
 	 */
 	public int getChildCount() {
 		return childCnt;
 	}
 
 	/**
 	 * Get the i-th child cache tree.
 	 *
 	 * @param i
 	 *            index of the child to obtain.
 	 * @return the child tree.
 	 */
 	public DirCacheTree getChild(int i) {
 		return children[i];
 	}
 
 	/**
 	 * Get the tree's ObjectId.
 	 * <p>
 	 * If {@link #isValid()} returns false this method will return null.
 	 *
 	 * @return ObjectId of this tree or null.
 	 * @since 4.3
 	 */
 	public ObjectId getObjectId() {
 		return id;
 	}
 
 	/**
 	 * Get the tree's name within its parent.
 	 * <p>
 	 * This method is not very efficient and is primarily meant for debugging
 	 * and final output generation. Applications should try to avoid calling it,
 	 * and if invoked do so only once per interesting entry, where the name is
 	 * absolutely required for correct function.
 	 *
 	 * @return name of the tree. This does not contain any '/' characters.
 	 */
 	public String getNameString() {
 		final ByteBuffer bb = ByteBuffer.wrap(encodedName);
 		return UTF_8.decode(bb).toString();
 	}
 
 	/**
 	 * Get the tree's path within the repository.
 	 * <p>
 	 * This method is not very efficient and is primarily meant for debugging
 	 * and final output generation. Applications should try to avoid calling it,
 	 * and if invoked do so only once per interesting entry, where the name is
 	 * absolutely required for correct function.
 	 *
 	 * @return path of the tree, relative to the repository root. If this is not
 	 *         the root tree the path ends with '/'. The root tree's path string
 	 *         is the empty string ("").
 	 */
 	public String getPathString() {
 		final StringBuilder r = new StringBuilder();
 		appendName(r);
 		return r.toString();
 	}
 
 	/**
 	 * Write (if necessary) this tree to the object store.
 	 *
 	 * @param cache
 	 *            the complete cache from DirCache.
 	 * @param cIdx
 	 *            first position of <code>cache</code> that is a member of this
 	 *            tree. The path of <code>cache[cacheIdx].path</code> for the
 	 *            range <code>[0,pathOff-1)</code> matches the complete path of
 	 *            this tree, from the root of the repository.
 	 * @param pathOffset
 	 *            number of bytes of <code>cache[cacheIdx].path</code> that
 	 *            matches this tree's path. The value at array position
 	 *            <code>cache[cacheIdx].path[pathOff-1]</code> is always '/' if
 	 *            <code>pathOff</code> is &gt; 0.
 	 * @param ow
 	 *            the writer to use when serializing to the store.
 	 * @return identity of this tree.
 	 * @throws UnmergedPathException
 	 *             one or more paths contain higher-order stages (stage &gt; 0),
 	 *             which cannot be stored in a tree object.
 	 * @throws IOException
 	 *             an unexpected error occurred writing to the object store.
 	 */
 	ObjectId writeTree(final DirCacheEntry[] cache, int cIdx,
 			final int pathOffset, final ObjectInserter ow)
 			throws UnmergedPathException, IOException {
 		if (id == null) {
 			final int endIdx = cIdx + entrySpan;
 			final TreeFormatter fmt = new TreeFormatter(computeSize(cache,
 					cIdx, pathOffset, ow));
 			int childIdx = 0;
 			int entryIdx = cIdx;
 
 			while (entryIdx < endIdx) {
 				final DirCacheEntry e = cache[entryIdx];
 				final byte[] ep = e.path;
 				if (childIdx < childCnt) {
 					final DirCacheTree st = children[childIdx];
 					if (st.contains(ep, pathOffset, ep.length)) {
 						fmt.append(st.encodedName, TREE, st.id);
 						entryIdx += st.entrySpan;
 						childIdx++;
 						continue;
 					}
 				}
 
 				fmt.append(ep, pathOffset, ep.length - pathOffset, e
 						.getFileMode(), e.idBuffer(), e.idOffset());
 				entryIdx++;
 			}
 
 			id = ow.insert(fmt);
 		}
 		return id;
 	}
 
 	private int computeSize(final DirCacheEntry[] cache, int cIdx,
 			final int pathOffset, final ObjectInserter ow)
 			throws UnmergedPathException, IOException {
 		final int endIdx = cIdx + entrySpan;
 		int childIdx = 0;
 		int entryIdx = cIdx;
 		int size = 0;
 
 		while (entryIdx < endIdx) {
 			final DirCacheEntry e = cache[entryIdx];
 			if (e.getStage() != 0)
 				throw new UnmergedPathException(e);
 
 			final byte[] ep = e.path;
 			if (childIdx < childCnt) {
 				final DirCacheTree st = children[childIdx];
 				if (st.contains(ep, pathOffset, ep.length)) {
 					final int stOffset = pathOffset + st.nameLength() + 1;
 					st.writeTree(cache, entryIdx, stOffset, ow);
 
 					size += entrySize(TREE, st.nameLength());
 
 					entryIdx += st.entrySpan;
 					childIdx++;
 					continue;
 				}
 			}
 
 			size += entrySize(e.getFileMode(), ep.length - pathOffset);
 			entryIdx++;
 		}
 
 		return size;
 	}
 
 	private void appendName(StringBuilder r) {
 		if (parent != null) {
 			parent.appendName(r);
 			r.append(getNameString());
 			r.append('/');
 		} else if (nameLength() > 0) {
 			r.append(getNameString());
 			r.append('/');
 		}
 	}
 
 	final int nameLength() {
 		return encodedName.length;
 	}
 
 	final boolean contains(byte[] a, int aOff, int aLen) {
 		final byte[] e = encodedName;
 		final int eLen = e.length;
 		for (int eOff = 0; eOff < eLen && aOff < aLen; eOff++, aOff++)
 			if (e[eOff] != a[aOff])
 				return false;
 		if (aOff >= aLen)
 			return false;
 		return a[aOff] == '/';
 	}
 
 	/**
 	 * Update (if necessary) this tree's entrySpan.
 	 *
 	 * @param cache
 	 *            the complete cache from DirCache.
 	 * @param cCnt
 	 *            number of entries in <code>cache</code> that are valid for
 	 *            iteration.
 	 * @param cIdx
 	 *            first position of <code>cache</code> that is a member of this
 	 *            tree. The path of <code>cache[cacheIdx].path</code> for the
 	 *            range <code>[0,pathOff-1)</code> matches the complete path of
 	 *            this tree, from the root of the repository.
 	 * @param pathOff
 	 *            number of bytes of <code>cache[cacheIdx].path</code> that
 	 *            matches this tree's path. The value at array position
 	 *            <code>cache[cacheIdx].path[pathOff-1]</code> is always '/' if
 	 *            <code>pathOff</code> is &gt; 0.
 	 */
 	void validate(final DirCacheEntry[] cache, final int cCnt, int cIdx,
 			final int pathOff) {
 		if (entrySpan >= 0 && cIdx + entrySpan <= cCnt) {
 			// If we are valid, our children are also valid.
 			// We have no need to validate them.
 			//
 			return;
 		}
 
 		entrySpan = 0;
 		if (cCnt == 0) {
 			// Special case of an empty index, and we are the root tree.
 			//
 			return;
 		}
 
 		final byte[] firstPath = cache[cIdx].path;
 		int stIdx = 0;
 		while (cIdx < cCnt) {
 			final byte[] currPath = cache[cIdx].path;
 			if (pathOff > 0 && !peq(firstPath, currPath, pathOff)) {
 				// The current entry is no longer in this tree. Our
 				// span is updated and the remainder goes elsewhere.
 				//
 				break;
 			}
 
 			DirCacheTree st = stIdx < childCnt ? children[stIdx] : null;
 			final int cc = namecmp(currPath, pathOff, st);
 			if (cc > 0) {
 				// This subtree is now empty.
 				//
 				removeChild(stIdx);
 				continue;
 			}
 
 			if (cc < 0) {
 				final int p = slash(currPath, pathOff);
 				if (p < 0) {
 					// The entry has no '/' and thus is directly in this
 					// tree. Count it as one of our own.
 					//
 					cIdx++;
 					entrySpan++;
 					continue;
 				}
 
 				// Build a new subtree for this entry.
 				//
 				st = new DirCacheTree(this, currPath, pathOff, p - pathOff);
 				insertChild(stIdx, st);
 			}
 
 			// The entry is contained in this subtree.
 			//
 			assert(st != null);
 			st.validate(cache, cCnt, cIdx, pathOff + st.nameLength() + 1);
 			cIdx += st.entrySpan;
 			entrySpan += st.entrySpan;
 			stIdx++;
 		}
 
 		// None of our remaining children can be in this tree
 		// as the current cache entry is after our own name.
 		//
 		while (stIdx < childCnt)
 			removeChild(childCnt - 1);
 	}
 
 	private void insertChild(int stIdx, DirCacheTree st) {
 		final DirCacheTree[] c = children;
 		if (childCnt + 1 <= c.length) {
 			if (stIdx < childCnt)
 				System.arraycopy(c, stIdx, c, stIdx + 1, childCnt - stIdx);
 			c[stIdx] = st;
 			childCnt++;
 			return;
 		}
 
 		final int n = c.length;
 		final DirCacheTree[] a = new DirCacheTree[n + 1];
 		if (stIdx > 0)
 			System.arraycopy(c, 0, a, 0, stIdx);
 		a[stIdx] = st;
 		if (stIdx < n)
 			System.arraycopy(c, stIdx, a, stIdx + 1, n - stIdx);
 		children = a;
 		childCnt++;
 	}
 
 	private void removeChild(int stIdx) {
 		final int n = --childCnt;
 		if (stIdx < n)
 			System.arraycopy(children, stIdx + 1, children, stIdx, n - stIdx);
 		children[n] = null;
 	}
 
 	static boolean peq(byte[] a, byte[] b, int aLen) {
 		if (b.length < aLen)
 			return false;
 		for (aLen--; aLen >= 0; aLen--)
 			if (a[aLen] != b[aLen])
 				return false;
 		return true;
 	}
 
 	private static int namecmp(byte[] a, int aPos, DirCacheTree ct) {
 		if (ct == null)
 			return -1;
 		final byte[] b = ct.encodedName;
 		final int aLen = a.length;
 		final int bLen = b.length;
 		int bPos = 0;
 		for (; aPos < aLen && bPos < bLen; aPos++, bPos++) {
 			final int cmp = (a[aPos] & 0xff) - (b[bPos] & 0xff);
 			if (cmp != 0)
 				return cmp;
 		}
 		if (bPos == bLen)
 			return a[aPos] == '/' ? 0 : -1;
 		return aLen - bLen;
 	}
 
 	private static int slash(byte[] a, int aPos) {
 		final int aLen = a.length;
 		for (; aPos < aLen; aPos++)
 			if (a[aPos] == '/')
 				return aPos;
 		return -1;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public String toString() {
 		return getNameString();
 	}
 }