Simplify and micro-optimize WorkingTreeIterator.ENTRY_CMP

[egit/fonseca.git] / org.spearce.jgit / src / org / spearce / jgit / treewalk / WorkingTreeIterator.java

/*
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
 *
 * 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 Git Development Community 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.spearce.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.spearce.jgit.errors.CorruptObjectException;
import org.spearce.jgit.lib.Constants;
import org.spearce.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 & 0170000) {
                case 0100000: /* normal files */
                        contentIdFromPtr = ptr;
                        return contentId = idBufferBlob(entries[ptr]);
                case 0120000: /* symbolic links */
                        // Java does not support symbolic links, so we should not
                        // have reached this particular part of the walk code.
                        //
                        return zeroid;
                case 0160000: /* 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;
                while (pathOffset + nameLen > path.length)
                        growPath(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';
        }

        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 (parent == null && ".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;
        }
}