/*
 * 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.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.CharacterCodingException;
import java.nio.charset.CharsetEncoder;
import java.security.MessageDigest;
import java.util.Arrays;
import java.util.Comparator;

import org.eclipse.jgit.errors.CorruptObjectException;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.FileMode;

/**
 * Walks a working directory tree as part of a {@link TreeWalk}.
 * <p>
 * Most applications will want to use the standard implementation of this
 * iterator, {@link FileTreeIterator}, as that does all IO through the standard
 * <code>java.io</code> package. Plugins for a Java based IDE may however wish
 * to create their own implementations of this class to allow traversal of the
 * IDE's project space, as well as benefit from any caching the IDE may have.
 *
 * @see FileTreeIterator
 */
public abstract class WorkingTreeIterator extends AbstractTreeIterator {
	/** An empty entry array, suitable for {@link #init(Entry[])}. */
	protected static final Entry[] EOF = {};

	/** Size we perform file IO in if we have to read and hash a file. */
	private static final int BUFFER_SIZE = 2048;

	/** The {@link #idBuffer()} for the current entry. */
	private byte[] contentId;

	/** Index within {@link #entries} that {@link #contentId} came from. */
	private int contentIdFromPtr;

	/** Buffer used to perform {@link #contentId} computations. */
	private byte[] contentReadBuffer;

	/** Digest computer for {@link #contentId} computations. */
	private MessageDigest contentDigest;

	/** File name character encoder. */
	private final CharsetEncoder nameEncoder;

	/** List of entries obtained from the subclass. */
	private Entry[] entries;

	/** Total number of entries in {@link #entries} that are valid. */
	private int entryCnt;

	/** Current position within {@link #entries}. */
	private int ptr;

	/** Create a new iterator with no parent. */
	protected WorkingTreeIterator() {
		super();
		nameEncoder = Constants.CHARSET.newEncoder();
	}

	/**
	 * 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 WorkingTreeIterator(final String prefix) {
		super(prefix);
		nameEncoder = Constants.CHARSET.newEncoder();
	}

	/**
	 * Create an iterator for a subtree of an existing iterator.
	 *
	 * @param p
	 *            parent tree iterator.
	 */
	protected WorkingTreeIterator(final WorkingTreeIterator p) {
		super(p);
		nameEncoder = p.nameEncoder;
	}

	@Override
	public byte[] idBuffer() {
		if (contentIdFromPtr == ptr)
			return contentId;
		switch (mode & FileMode.TYPE_MASK) {
		case FileMode.TYPE_FILE:
			contentIdFromPtr = ptr;
			return contentId = idBufferBlob(entries[ptr]);
		case FileMode.TYPE_SYMLINK:
			// Java does not support symbolic links, so we should not
			// have reached this particular part of the walk code.
			//
			return zeroid;
		case FileMode.TYPE_GITLINK:
			// TODO: Support obtaining current HEAD SHA-1 from nested repository
			//
			return zeroid;
		}
		return zeroid;
	}

	private void initializeDigest() {
		if (contentDigest != null)
			return;

		if (parent == null) {
			contentReadBuffer = new byte[BUFFER_SIZE];
			contentDigest = Constants.newMessageDigest();
		} else {
			final WorkingTreeIterator p = (WorkingTreeIterator) parent;
			p.initializeDigest();
			contentReadBuffer = p.contentReadBuffer;
			contentDigest = p.contentDigest;
		}
	}

	private static final byte[] digits = { '0', '1', '2', '3', '4', '5', '6',
			'7', '8', '9' };

	private static final byte[] hblob = Constants
			.encodedTypeString(Constants.OBJ_BLOB);

	private byte[] idBufferBlob(final Entry e) {
		try {
			final InputStream is = e.openInputStream();
			if (is == null)
				return zeroid;
			try {
				initializeDigest();

				contentDigest.reset();
				contentDigest.update(hblob);
				contentDigest.update((byte) ' ');

				final long blobLength = e.getLength();
				long sz = blobLength;
				if (sz == 0) {
					contentDigest.update((byte) '0');
				} else {
					final int bufn = contentReadBuffer.length;
					int p = bufn;
					do {
						contentReadBuffer[--p] = digits[(int) (sz % 10)];
						sz /= 10;
					} while (sz > 0);
					contentDigest.update(contentReadBuffer, p, bufn - p);
				}
				contentDigest.update((byte) 0);

				for (;;) {
					final int r = is.read(contentReadBuffer);
					if (r <= 0)
						break;
					contentDigest.update(contentReadBuffer, 0, r);
					sz += r;
				}
				if (sz != blobLength)
					return zeroid;
				return contentDigest.digest();
			} finally {
				try {
					is.close();
				} catch (IOException err2) {
					// Suppress any error related to closing an input
					// stream. We don't care, we should not have any
					// outstanding data to flush or anything like that.
				}
			}
		} catch (IOException err) {
			// Can't read the file? Don't report the failure either.
			//
			return zeroid;
		}
	}

	@Override
	public int idOffset() {
		return 0;
	}

	@Override
	public boolean first() {
		return ptr == 0;
	}

	@Override
	public boolean eof() {
		return ptr == entryCnt;
	}

	@Override
	public void next(final int delta) throws CorruptObjectException {
		ptr += delta;
		if (!eof())
			parseEntry();
	}

	@Override
	public void back(final int delta) throws CorruptObjectException {
		ptr -= delta;
		parseEntry();
	}

	private void parseEntry() {
		final Entry e = entries[ptr];
		mode = e.getMode().getBits();

		final int nameLen = e.encodedNameLen;
		ensurePathCapacity(pathOffset + nameLen, pathOffset);
		System.arraycopy(e.encodedName, 0, path, pathOffset, nameLen);
		pathLen = pathOffset + nameLen;
	}

	/**
	 * Get the byte length of this entry.
	 *
	 * @return size of this file, in bytes.
	 */
	public long getEntryLength() {
		return current().getLength();
	}

	/**
	 * Get the last modified time of this entry.
	 *
	 * @return last modified time of this file, in milliseconds since the epoch
	 *         (Jan 1, 1970 UTC).
	 */
	public long getEntryLastModified() {
		return current().getLastModified();
	}

	private static final Comparator<Entry> ENTRY_CMP = new Comparator<Entry>() {
		public int compare(final Entry o1, final Entry o2) {
			final byte[] a = o1.encodedName;
			final byte[] b = o2.encodedName;
			final int aLen = o1.encodedNameLen;
			final int bLen = o2.encodedNameLen;
			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 (cPos < aLen)
				return (a[cPos] & 0xff) - lastPathChar(o2);
			if (cPos < bLen)
				return lastPathChar(o1) - (b[cPos] & 0xff);
			return lastPathChar(o1) - lastPathChar(o2);
		}
	};

	static int lastPathChar(final Entry e) {
		return e.getMode() == FileMode.TREE ? '/' : '\0';
	}

	/**
	 * Constructor helper.
	 *
	 * @param list
	 *            files in the subtree of the work tree this iterator operates
	 *            on
	 */
	protected void init(final Entry[] list) {
		// Filter out nulls, . and .. as these are not valid tree entries,
		// also cache the encoded forms of the path names for efficient use
		// later on during sorting and iteration.
		//
		entries = list;
		int i, o;

		for (i = 0, o = 0; i < entries.length; i++) {
			final Entry e = entries[i];
			if (e == null)
				continue;
			final String name = e.getName();
			if (".".equals(name) || "..".equals(name))
				continue;
			if (Constants.DOT_GIT.equals(name))
				continue;
			if (i != o)
				entries[o] = e;
			e.encodeName(nameEncoder);
			o++;
		}
		entryCnt = o;
		Arrays.sort(entries, 0, entryCnt, ENTRY_CMP);

		contentIdFromPtr = -1;
		ptr = 0;
		if (!eof())
			parseEntry();
	}

	/**
	 * Obtain the current entry from this iterator.
	 *
	 * @return the currently selected entry.
	 */
	protected Entry current() {
		return entries[ptr];
	}

	/** A single entry within a working directory tree. */
	protected static abstract class Entry {
		byte[] encodedName;

		int encodedNameLen;

		void encodeName(final CharsetEncoder enc) {
			final ByteBuffer b;
			try {
				b = enc.encode(CharBuffer.wrap(getName()));
			} catch (CharacterCodingException e) {
				// This should so never happen.
				throw new RuntimeException("Unencodeable file: " + getName());
			}

			encodedNameLen = b.limit();
			if (b.hasArray() && b.arrayOffset() == 0)
				encodedName = b.array();
			else
				b.get(encodedName = new byte[encodedNameLen]);
		}

		public String toString() {
			return getMode().toString() + " " + getName();
		}

		/**
		 * Get the type of this entry.
		 * <p>
		 * <b>Note: Efficient implementation required.</b>
		 * <p>
		 * The implementation of this method must be efficient. If a subclass
		 * needs to compute the value they should cache the reference within an
		 * instance member instead.
		 *
		 * @return a file mode constant from {@link FileMode}.
		 */
		public abstract FileMode getMode();

		/**
		 * Get the byte length of this entry.
		 * <p>
		 * <b>Note: Efficient implementation required.</b>
		 * <p>
		 * The implementation of this method must be efficient. If a subclass
		 * needs to compute the value they should cache the reference within an
		 * instance member instead.
		 *
		 * @return size of this file, in bytes.
		 */
		public abstract long getLength();

		/**
		 * Get the last modified time of this entry.
		 * <p>
		 * <b>Note: Efficient implementation required.</b>
		 * <p>
		 * The implementation of this method must be efficient. If a subclass
		 * needs to compute the value they should cache the reference within an
		 * instance member instead.
		 *
		 * @return time since the epoch (in ms) of the last change.
		 */
		public abstract long getLastModified();

		/**
		 * Get the name of this entry within its directory.
		 * <p>
		 * Efficient implementations are not required. The caller will obtain
		 * the name only once and cache it once obtained.
		 *
		 * @return name of the entry.
		 */
		public abstract String getName();

		/**
		 * Obtain an input stream to read the file content.
		 * <p>
		 * Efficient implementations are not required. The caller will usually
		 * obtain the stream only once per entry, if at all.
		 * <p>
		 * The input stream should not use buffering if the implementation can
		 * avoid it. The caller will buffer as necessary to perform efficient
		 * block IO operations.
		 * <p>
		 * The caller will close the stream once complete.
		 *
		 * @return a stream to read from the file.
		 * @throws IOException
		 *             the file could not be opened for reading.
		 */
		public abstract InputStream openInputStream() throws IOException;
	}
}