/*
 * Copyright (C) 2008-2009, Google Inc.
 * Copyright (C) 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
 * 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,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.eclipse.jgit.treewalk;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;

import org.eclipse.jgit.errors.CorruptObjectException;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
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.Repository;
import org.eclipse.jgit.lib.WindowCursor;
import org.eclipse.jgit.treewalk.filter.TreeFilter;

/**
 * Walks a Git tree (directory) in Git sort order.
 * <p>
 * A new iterator instance should be positioned on the first entry, or at eof.
 * Data for the first entry (if not at eof) should be available immediately.
 * <p>
 * Implementors must walk a tree in the Git sort order, which has the following
 * odd sorting:
 * <ol>
 * <li>A.c</li>
 * <li>A/c</li>
 * <li>A0c</li>
 * </ol>
 * <p>
 * In the second item, <code>A</code> is the name of a subtree and
 * <code>c</code> is a file within that subtree. The other two items are files
 * in the root level tree.
 *
 * @see CanonicalTreeParser
 */
public abstract class AbstractTreeIterator {
	/** Default size for the {@link #path} buffer. */
	protected static final int DEFAULT_PATH_SIZE = 128;

	/** A dummy object id buffer that matches the zero ObjectId. */
	protected static final byte[] zeroid = new byte[Constants.OBJECT_ID_LENGTH];

	/** Iterator for the parent tree; null if we are the root iterator. */
	final AbstractTreeIterator parent;

	/** The iterator this current entry is path equal to. */
	AbstractTreeIterator matches;

	/**
	 * Number of entries we moved forward to force a D/F conflict match.
	 *
	 * @see NameConflictTreeWalk
	 */
	int matchShift;

	/**
	 * Mode bits for the current entry.
	 * <p>
	 * A numerical value from FileMode is usually faster for an iterator to
	 * obtain from its data source so this is the preferred representation.
	 *
	 * @see org.eclipse.jgit.lib.FileMode
	 */
	protected int mode;

	/**
	 * Path buffer for the current entry.
	 * <p>
	 * This buffer is pre-allocated at the start of walking and is shared from
	 * parent iterators down into their subtree iterators. The sharing allows
	 * the current entry to always be a full path from the root, while each
	 * subtree only needs to populate the part that is under their control.
	 */
	protected byte[] path;

	/**
	 * Position within {@link #path} this iterator starts writing at.
	 * <p>
	 * This is the first offset in {@link #path} that this iterator must
	 * populate during {@link #next}. At the root level (when {@link #parent}
	 * is null) this is 0. For a subtree iterator the index before this position
	 * should have the value '/'.
	 */
	protected final int pathOffset;

	/**
	 * Total length of the current entry's complete path from the root.
	 * <p>
	 * This is the number of bytes within {@link #path} that pertain to the
	 * current entry. Values at this index through the end of the array are
	 * garbage and may be randomly populated from prior entries.
	 */
	protected int pathLen;

	/** Create a new iterator with no parent. */
	protected AbstractTreeIterator() {
		parent = null;
		path = new byte[DEFAULT_PATH_SIZE];
		pathOffset = 0;
	}

	/**
	 * Create a new iterator with no parent and a prefix.
	 * <p>
	 * The prefix path supplied is inserted in front of all paths generated by
	 * this iterator. It is intended to be used when an iterator is being
	 * created for a subsection of an overall repository and needs to be
	 * combined with other iterators that are created to run over the entire
	 * repository namespace.
	 *
	 * @param prefix
	 *            position of this iterator in the repository tree. The value
	 *            may be null or the empty string to indicate the prefix is the
	 *            root of the repository. A trailing slash ('/') is
	 *            automatically appended if the prefix does not end in '/'.
	 */
	protected AbstractTreeIterator(final String prefix) {
		parent = null;

		if (prefix != null && prefix.length() > 0) {
			final ByteBuffer b;

			b = Constants.CHARSET.encode(CharBuffer.wrap(prefix));
			pathLen = b.limit();
			path = new byte[Math.max(DEFAULT_PATH_SIZE, pathLen + 1)];
			b.get(path, 0, pathLen);
			if (path[pathLen - 1] != '/')
				path[pathLen++] = '/';
			pathOffset = pathLen;
		} else {
			path = new byte[DEFAULT_PATH_SIZE];
			pathOffset = 0;
		}
	}

	/**
	 * Create a new iterator with no parent and a prefix.
	 * <p>
	 * The prefix path supplied is inserted in front of all paths generated by
	 * this iterator. It is intended to be used when an iterator is being
	 * created for a subsection of an overall repository and needs to be
	 * combined with other iterators that are created to run over the entire
	 * repository namespace.
	 *
	 * @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 '/'.
	 */
	protected AbstractTreeIterator(final byte[] prefix) {
		parent = null;

		if (prefix != null && prefix.length > 0) {
			pathLen = prefix.length;
			path = new byte[Math.max(DEFAULT_PATH_SIZE, pathLen + 1)];
			System.arraycopy(prefix, 0, path, 0, pathLen);
			if (path[pathLen - 1] != '/')
				path[pathLen++] = '/';
			pathOffset = pathLen;
		} else {
			path = new byte[DEFAULT_PATH_SIZE];
			pathOffset = 0;
		}
	}

	/**
	 * Create an iterator for a subtree of an existing iterator.
	 *
	 * @param p
	 *            parent tree iterator.
	 */
	protected AbstractTreeIterator(final AbstractTreeIterator p) {
		parent = p;
		path = p.path;
		pathOffset = p.pathLen + 1;
		try {
			path[pathOffset - 1] = '/';
		} catch (ArrayIndexOutOfBoundsException e) {
			growPath(p.pathLen);
			path[pathOffset - 1] = '/';
		}
	}

	/**
	 * Create an iterator for a subtree of an existing iterator.
	 * <p>
	 * The caller is responsible for setting up the path of the child iterator.
	 *
	 * @param p
	 *            parent tree iterator.
	 * @param childPath
	 *            path array to be used by the child iterator. This path must
	 *            contain the path from the top of the walk to the first child
	 *            and must end with a '/'.
	 * @param childPathOffset
	 *            position within <code>childPath</code> where the child can
	 *            insert its data. The value at
	 *            <code>childPath[childPathOffset-1]</code> must be '/'.
	 */
	protected AbstractTreeIterator(final AbstractTreeIterator p,
			final byte[] childPath, final int childPathOffset) {
		parent = p;
		path = childPath;
		pathOffset = childPathOffset;
	}

	/**
	 * Grow the path buffer larger.
	 *
	 * @param len
	 *            number of live bytes in the path buffer. This many bytes will
	 *            be moved into the larger buffer.
	 */
	protected void growPath(final int len) {
		setPathCapacity(path.length << 1, len);
	}

	/**
	 * Ensure that path is capable to hold at least {@code capacity} bytes
	 *
	 * @param capacity
	 *            the amount of bytes to hold
	 * @param len
	 *            the amount of live bytes in path buffer
	 */
	protected void ensurePathCapacity(final int capacity, final int len) {
		if (path.length >= capacity)
			return;
		final byte[] o = path;
		int current = o.length;
		int newCapacity = current;
		while (newCapacity < capacity && newCapacity > 0)
			newCapacity <<= 1;
		setPathCapacity(newCapacity, len);
	}

	/**
	 * Set path buffer capacity to the specified size
	 *
	 * @param capacity
	 *            the new size
	 * @param len
	 *            the amount of bytes to copy
	 */
	private void setPathCapacity(int capacity, int len) {
		final byte[] o = path;
		final byte[] n = new byte[capacity];
		System.arraycopy(o, 0, n, 0, len);
		for (AbstractTreeIterator p = this; p != null && p.path == o; p = p.parent)
			p.path = n;
	}

	/**
	 * Compare the path of this current entry to another iterator's entry.
	 *
	 * @param p
	 *            the other iterator to compare the path against.
	 * @return -1 if this entry sorts first; 0 if the entries are equal; 1 if
	 *         p's entry sorts first.
	 */
	public int pathCompare(final AbstractTreeIterator p) {
		return pathCompare(p, p.mode);
	}

	int pathCompare(final AbstractTreeIterator p, final int pMode) {
		final byte[] a = path;
		final byte[] b = p.path;
		final int aLen = pathLen;
		final int bLen = p.pathLen;
		int cPos;

		// Its common when we are a subtree for both parents to match;
		// when this happens everything in path[0..cPos] is known to
		// be equal and does not require evaluation again.
		//
		cPos = alreadyMatch(this, p);

		for (; cPos < aLen && cPos < bLen; cPos++) {
			final int cmp = (a[cPos] & 0xff) - (b[cPos] & 0xff);
			if (cmp != 0)
				return cmp;
		}

		if (cPos < aLen)
			return (a[cPos] & 0xff) - lastPathChar(pMode);
		if (cPos < bLen)
			return lastPathChar(mode) - (b[cPos] & 0xff);
		return lastPathChar(mode) - lastPathChar(pMode);
	}

	private static int alreadyMatch(AbstractTreeIterator a,
			AbstractTreeIterator b) {
		for (;;) {
			final AbstractTreeIterator ap = a.parent;
			final AbstractTreeIterator bp = b.parent;
			if (ap == null || bp == null)
				return 0;
			if (ap.matches == bp.matches)
				return a.pathOffset;
			a = ap;
			b = bp;
		}
	}

	private static int lastPathChar(final int mode) {
		return FileMode.TREE.equals(mode) ? '/' : '\0';
	}

	/**
	 * Check if the current entry of both iterators has the same id.
	 * <p>
	 * This method is faster than {@link #getEntryObjectId()} as it does not
	 * require copying the bytes out of the buffers. A direct {@link #idBuffer}
	 * compare operation is performed.
	 *
	 * @param otherIterator
	 *            the other iterator to test against.
	 * @return true if both iterators have the same object id; false otherwise.
	 */
	public boolean idEqual(final AbstractTreeIterator otherIterator) {
		return ObjectId.equals(idBuffer(), idOffset(),
				otherIterator.idBuffer(), otherIterator.idOffset());
	}

	/**
	 * Get the object id of the current entry.
	 *
	 * @return an object id for the current entry.
	 */
	public ObjectId getEntryObjectId() {
		return ObjectId.fromRaw(idBuffer(), idOffset());
	}

	/**
	 * Obtain the ObjectId for the current entry.
	 *
	 * @param out
	 *            buffer to copy the object id into.
	 */
	public void getEntryObjectId(final MutableObjectId out) {
		out.fromRaw(idBuffer(), idOffset());
	}

	/** @return the file mode of the current entry. */
	public FileMode getEntryFileMode() {
		return FileMode.fromBits(mode);
	}

	/** @return the file mode of the current entry as bits */
	public int getEntryRawMode() {
		return mode;
	}

	/** @return path of the current entry, as a string. */
	public String getEntryPathString() {
		return TreeWalk.pathOf(this);
	}

	/**
	 * Get the byte array buffer object IDs must be copied out of.
	 * <p>
	 * The id buffer contains the bytes necessary to construct an ObjectId for
	 * the current entry of this iterator. The buffer can be the same buffer for
	 * all entries, or it can be a unique buffer per-entry. Implementations are
	 * encouraged to expose their private buffer whenever possible to reduce
	 * garbage generation and copying costs.
	 *
	 * @return byte array the implementation stores object IDs within.
	 * @see #getEntryObjectId()
	 */
	public abstract byte[] idBuffer();

	/**
	 * Get the position within {@link #idBuffer()} of this entry's ObjectId.
	 *
	 * @return offset into the array returned by {@link #idBuffer()} where the
	 *         ObjectId must be copied out of.
	 */
	public abstract int idOffset();

	/**
	 * Create a new iterator for the current entry's subtree.
	 * <p>
	 * The parent reference of the iterator must be <code>this</code>,
	 * otherwise the caller would not be able to exit out of the subtree
	 * iterator correctly and return to continue walking <code>this</code>.
	 *
	 * @param repo
	 *            repository to load the tree data from.
	 * @return a new parser that walks over the current subtree.
	 * @throws IncorrectObjectTypeException
	 *             the current entry 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 abstract AbstractTreeIterator createSubtreeIterator(Repository repo)
			throws IncorrectObjectTypeException, IOException;

	/**
	 * Create a new iterator as though the current entry were a subtree.
	 *
	 * @return a new empty tree iterator.
	 */
	public EmptyTreeIterator createEmptyTreeIterator() {
		return new EmptyTreeIterator(this);
	}

	/**
	 * Create a new iterator for the current entry's subtree.
	 * <p>
	 * The parent reference of the iterator must be <code>this</code>, otherwise
	 * the caller would not be able to exit out of the subtree iterator
	 * correctly and return to continue walking <code>this</code>.
	 *
	 * @param repo
	 *            repository to load the tree data from.
	 * @param idBuffer
	 *            temporary ObjectId buffer for use by this method.
	 * @param curs
	 *            window cursor to use during repository access.
	 * @return a new parser that walks over the current subtree.
	 * @throws IncorrectObjectTypeException
	 *             the current entry 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 AbstractTreeIterator createSubtreeIterator(final Repository repo,
			final MutableObjectId idBuffer, final WindowCursor curs)
			throws IncorrectObjectTypeException, IOException {
		return createSubtreeIterator(repo);
	}

	/**
	 * Is this tree iterator positioned on its first entry?
	 * <p>
	 * An iterator is positioned on the first entry if <code>back(1)</code>
	 * would be an invalid request as there is no entry before the current one.
	 * <p>
	 * An empty iterator (one with no entries) will be
	 * <code>first() &amp;&amp; eof()</code>.
	 *
	 * @return true if the iterator is positioned on the first entry.
	 */
	public abstract boolean first();

	/**
	 * Is this tree iterator at its EOF point (no more entries)?
	 * <p>
	 * An iterator is at EOF if there is no current entry.
	 *
	 * @return true if we have walked all entries and have none left.
	 */
	public abstract boolean eof();

	/**
	 * Move to next entry, populating this iterator with the entry data.
	 * <p>
	 * The delta indicates how many moves forward should occur. The most common
	 * delta is 1 to move to the next entry.
	 * <p>
	 * Implementations must populate the following members:
	 * <ul>
	 * <li>{@link #mode}</li>
	 * <li>{@link #path} (from {@link #pathOffset} to {@link #pathLen})</li>
	 * <li>{@link #pathLen}</li>
	 * </ul>
	 * as well as any implementation dependent information necessary to
	 * accurately return data from {@link #idBuffer()} and {@link #idOffset()}
	 * when demanded.
	 *
	 * @param delta
	 *            number of entries to move the iterator by. Must be a positive,
	 *            non-zero integer.
	 * @throws CorruptObjectException
	 *             the tree is invalid.
	 */
	public abstract void next(int delta) throws CorruptObjectException;

	/**
	 * Move to prior entry, populating this iterator with the entry data.
	 * <p>
	 * The delta indicates how many moves backward should occur.The most common
	 * delta is 1 to move to the prior entry.
	 * <p>
	 * Implementations must populate the following members:
	 * <ul>
	 * <li>{@link #mode}</li>
	 * <li>{@link #path} (from {@link #pathOffset} to {@link #pathLen})</li>
	 * <li>{@link #pathLen}</li>
	 * </ul>
	 * as well as any implementation dependent information necessary to
	 * accurately return data from {@link #idBuffer()} and {@link #idOffset()}
	 * when demanded.
	 *
	 * @param delta
	 *            number of entries to move the iterator by. Must be a positive,
	 *            non-zero integer.
	 * @throws CorruptObjectException
	 *             the tree is invalid.
	 */
	public abstract void back(int delta) throws CorruptObjectException;

	/**
	 * Advance to the next tree entry, populating this iterator with its data.
	 * <p>
	 * This method behaves like <code>seek(1)</code> but is called by
	 * {@link TreeWalk} only if a {@link TreeFilter} was used and ruled out the
	 * current entry from the results. In such cases this tree iterator may
	 * perform special behavior.
	 *
	 * @throws CorruptObjectException
	 *             the tree is invalid.
	 */
	public void skip() throws CorruptObjectException {
		next(1);
	}

	/**
	 * Indicates to the iterator that no more entries will be read.
	 * <p>
	 * This is only invoked by TreeWalk when the iteration is aborted early due
	 * to a {@link org.eclipse.jgit.errors.StopWalkException} being thrown from
	 * within a TreeFilter.
	 */
	public void stopWalk() {
		// Do nothing by default.  Most iterators do not care.
	}

	/**
	 * @return the length of the name component of the path for the current entry
	 */
	public int getNameLength() {
		return pathLen - pathOffset;
	}

	/**
	 * Get the name component of the current entry path into the provided buffer.
	 *
	 * @param buffer the buffer to get the name into, it is assumed that buffer can hold the name
	 * @param offset the offset of the name in the buffer
	 * @see #getNameLength()
	 */
	public void getName(byte[] buffer, int offset) {
		System.arraycopy(path, pathOffset, buffer, offset, pathLen - pathOffset);
	}
}