org.eclipse.jgit.diff.DiffFormatter.java Source code

Java tutorial

Introduction

Here is the source code for org.eclipse.jgit.diff.DiffFormatter.java

Source

/*
 * Copyright (C) 2009, Google Inc.
 * Copyright (C) 2008-2009, Johannes E. Schindelin <johannes.schindelin@gmx.de>
 * 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.diff;

import static org.eclipse.jgit.diff.DiffEntry.ChangeType.ADD;
import static org.eclipse.jgit.diff.DiffEntry.ChangeType.COPY;
import static org.eclipse.jgit.diff.DiffEntry.ChangeType.DELETE;
import static org.eclipse.jgit.diff.DiffEntry.ChangeType.MODIFY;
import static org.eclipse.jgit.diff.DiffEntry.ChangeType.RENAME;
import static org.eclipse.jgit.diff.DiffEntry.Side.NEW;
import static org.eclipse.jgit.diff.DiffEntry.Side.OLD;
import static org.eclipse.jgit.lib.Constants.encode;
import static org.eclipse.jgit.lib.Constants.encodeASCII;
import static org.eclipse.jgit.lib.FileMode.GITLINK;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Collection;
import java.util.Collections;
import java.util.List;

import org.eclipse.jgit.diff.DiffAlgorithm.SupportedAlgorithm;
import org.eclipse.jgit.diff.DiffEntry.ChangeType;
import org.eclipse.jgit.dircache.DirCacheIterator;
import org.eclipse.jgit.errors.AmbiguousObjectException;
import org.eclipse.jgit.errors.BinaryBlobException;
import org.eclipse.jgit.errors.CancelledException;
import org.eclipse.jgit.errors.CorruptObjectException;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.lib.AbbreviatedObjectId;
import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.Config;
import org.eclipse.jgit.lib.ConfigConstants;
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.lib.ProgressMonitor;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.patch.FileHeader;
import org.eclipse.jgit.patch.FileHeader.PatchType;
import org.eclipse.jgit.revwalk.FollowFilter;
import org.eclipse.jgit.revwalk.RevTree;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.storage.pack.PackConfig;
import org.eclipse.jgit.treewalk.AbstractTreeIterator;
import org.eclipse.jgit.treewalk.CanonicalTreeParser;
import org.eclipse.jgit.treewalk.EmptyTreeIterator;
import org.eclipse.jgit.treewalk.TreeWalk;
import org.eclipse.jgit.treewalk.WorkingTreeIterator;
import org.eclipse.jgit.treewalk.filter.AndTreeFilter;
import org.eclipse.jgit.treewalk.filter.IndexDiffFilter;
import org.eclipse.jgit.treewalk.filter.NotIgnoredFilter;
import org.eclipse.jgit.treewalk.filter.PathFilter;
import org.eclipse.jgit.treewalk.filter.TreeFilter;
import org.eclipse.jgit.util.LfsFactory;
import org.eclipse.jgit.util.QuotedString;

/**
 * Format a Git style patch script.
 */
public class DiffFormatter implements AutoCloseable {
    private static final int DEFAULT_BINARY_FILE_THRESHOLD = PackConfig.DEFAULT_BIG_FILE_THRESHOLD;

    private static final byte[] noNewLine = encodeASCII("\\ No newline at end of file\n"); //$NON-NLS-1$

    /** Magic return content indicating it is empty or no content present. */
    private static final byte[] EMPTY = new byte[] {};

    private final OutputStream out;

    private ObjectReader reader;

    private boolean closeReader;

    private DiffConfig diffCfg;

    private int context = 3;

    private int abbreviationLength = 7;

    private DiffAlgorithm diffAlgorithm;

    private RawTextComparator comparator = RawTextComparator.DEFAULT;

    private int binaryFileThreshold = DEFAULT_BINARY_FILE_THRESHOLD;

    private String oldPrefix = "a/"; //$NON-NLS-1$

    private String newPrefix = "b/"; //$NON-NLS-1$

    private TreeFilter pathFilter = TreeFilter.ALL;

    private RenameDetector renameDetector;

    private ProgressMonitor progressMonitor;

    private ContentSource.Pair source;

    private Repository repository;

    private Boolean quotePaths;

    /**
     * Create a new formatter with a default level of context.
     *
     * @param out
     *            the stream the formatter will write line data to. This stream
     *            should have buffering arranged by the caller, as many small
     *            writes are performed to it.
     */
    public DiffFormatter(OutputStream out) {
        this.out = out;
    }

    /**
     * Get output stream
     *
     * @return the stream we are outputting data to
     */
    protected OutputStream getOutputStream() {
        return out;
    }

    /**
     * Set the repository the formatter can load object contents from.
     *
     * Once a repository has been set, the formatter must be released to ensure
     * the internal ObjectReader is able to release its resources.
     *
     * @param repository
     *            source repository holding referenced objects.
     */
    public void setRepository(Repository repository) {
        this.repository = repository;
        setReader(repository.newObjectReader(), repository.getConfig(), true);
    }

    /**
     * Set the repository the formatter can load object contents from.
     *
     * @param reader
     *            source reader holding referenced objects. Caller is responsible
     *            for closing the reader.
     * @param cfg
     *            config specifying diff algorithm and rename detection options.
     * @since 4.5
     */
    public void setReader(ObjectReader reader, Config cfg) {
        setReader(reader, cfg, false);
    }

    private void setReader(ObjectReader reader, Config cfg, boolean closeReader) {
        close();
        this.closeReader = closeReader;
        this.reader = reader;
        this.diffCfg = cfg.get(DiffConfig.KEY);
        if (quotePaths == null) {
            quotePaths = Boolean.valueOf(cfg.getBoolean(ConfigConstants.CONFIG_CORE_SECTION,
                    ConfigConstants.CONFIG_KEY_QUOTE_PATH, true));
        }

        ContentSource cs = ContentSource.create(reader);
        source = new ContentSource.Pair(cs, cs);

        if (diffCfg.isNoPrefix()) {
            setOldPrefix(""); //$NON-NLS-1$
            setNewPrefix(""); //$NON-NLS-1$
        }
        setDetectRenames(diffCfg.isRenameDetectionEnabled());

        diffAlgorithm = DiffAlgorithm.getAlgorithm(cfg.getEnum(ConfigConstants.CONFIG_DIFF_SECTION, null,
                ConfigConstants.CONFIG_KEY_ALGORITHM, SupportedAlgorithm.HISTOGRAM));
    }

    /**
     * Change the number of lines of context to display.
     *
     * @param lineCount
     *            number of lines of context to see before the first
     *            modification and after the last modification within a hunk of
     *            the modified file.
     */
    public void setContext(int lineCount) {
        if (lineCount < 0)
            throw new IllegalArgumentException(JGitText.get().contextMustBeNonNegative);
        context = lineCount;
    }

    /**
     * Change the number of digits to show in an ObjectId.
     *
     * @param count
     *            number of digits to show in an ObjectId.
     */
    public void setAbbreviationLength(int count) {
        if (count < 0)
            throw new IllegalArgumentException(JGitText.get().abbreviationLengthMustBeNonNegative);
        abbreviationLength = count;
    }

    /**
     * Set the algorithm that constructs difference output.
     *
     * @param alg
     *            the algorithm to produce text file differences.
     * @see HistogramDiff
     */
    public void setDiffAlgorithm(DiffAlgorithm alg) {
        diffAlgorithm = alg;
    }

    /**
     * Set the line equivalence function for text file differences.
     *
     * @param cmp
     *            The equivalence function used to determine if two lines of
     *            text are identical. The function can be changed to ignore
     *            various types of whitespace.
     * @see RawTextComparator#DEFAULT
     * @see RawTextComparator#WS_IGNORE_ALL
     * @see RawTextComparator#WS_IGNORE_CHANGE
     * @see RawTextComparator#WS_IGNORE_LEADING
     * @see RawTextComparator#WS_IGNORE_TRAILING
     */
    public void setDiffComparator(RawTextComparator cmp) {
        comparator = cmp;
    }

    /**
     * Set maximum file size for text files.
     *
     * Files larger than this size will be treated as though they are binary and
     * not text. Default is {@value #DEFAULT_BINARY_FILE_THRESHOLD} .
     *
     * @param threshold
     *            the limit, in bytes. Files larger than this size will be
     *            assumed to be binary, even if they aren't.
     */
    public void setBinaryFileThreshold(int threshold) {
        this.binaryFileThreshold = threshold;
    }

    /**
     * Set the prefix applied in front of old file paths.
     *
     * @param prefix
     *            the prefix in front of old paths. Typically this is the
     *            standard string {@code "a/"}, but may be any prefix desired by
     *            the caller. Must not be null. Use the empty string to have no
     *            prefix at all.
     */
    public void setOldPrefix(String prefix) {
        oldPrefix = prefix;
    }

    /**
     * Get the prefix applied in front of old file paths.
     *
     * @return the prefix
     * @since 2.0
     */
    public String getOldPrefix() {
        return this.oldPrefix;
    }

    /**
     * Set the prefix applied in front of new file paths.
     *
     * @param prefix
     *            the prefix in front of new paths. Typically this is the
     *            standard string {@code "b/"}, but may be any prefix desired by
     *            the caller. Must not be null. Use the empty string to have no
     *            prefix at all.
     */
    public void setNewPrefix(String prefix) {
        newPrefix = prefix;
    }

    /**
     * Get the prefix applied in front of new file paths.
     *
     * @return the prefix
     * @since 2.0
     */
    public String getNewPrefix() {
        return this.newPrefix;
    }

    /**
     * Get if rename detection is enabled
     *
     * @return true if rename detection is enabled
     */
    public boolean isDetectRenames() {
        return renameDetector != null;
    }

    /**
     * Enable or disable rename detection.
     *
     * Before enabling rename detection the repository must be set with
     * {@link #setRepository(Repository)}. Once enabled the detector can be
     * configured away from its defaults by obtaining the instance directly from
     * {@link #getRenameDetector()} and invoking configuration.
     *
     * @param on
     *            if rename detection should be enabled.
     */
    public void setDetectRenames(boolean on) {
        if (on && renameDetector == null) {
            assertHaveReader();
            renameDetector = new RenameDetector(reader, diffCfg);
        } else if (!on)
            renameDetector = null;
    }

    /**
     * Get rename detector
     *
     * @return the rename detector if rename detection is enabled
     */
    public RenameDetector getRenameDetector() {
        return renameDetector;
    }

    /**
     * Set the progress monitor for long running rename detection.
     *
     * @param pm
     *            progress monitor to receive rename detection status through.
     */
    public void setProgressMonitor(ProgressMonitor pm) {
        progressMonitor = pm;
    }

    /**
     * Sets whether or not path names should be quoted.
     * <p>
     * By default the setting of git config {@code core.quotePath} is active,
     * but this can be overridden through this method.
     * </p>
     *
     * @param quote
     *            whether to quote path names
     * @since 5.6
     */
    public void setQuotePaths(boolean quote) {
        quotePaths = Boolean.valueOf(quote);
    }

    /**
     * Set the filter to produce only specific paths.
     *
     * If the filter is an instance of
     * {@link org.eclipse.jgit.revwalk.FollowFilter}, the filter path will be
     * updated during successive scan or format invocations. The updated path
     * can be obtained from {@link #getPathFilter()}.
     *
     * @param filter
     *            the tree filter to apply.
     */
    public void setPathFilter(TreeFilter filter) {
        pathFilter = filter != null ? filter : TreeFilter.ALL;
    }

    /**
     * Get path filter
     *
     * @return the current path filter
     */
    public TreeFilter getPathFilter() {
        return pathFilter;
    }

    /**
     * Flush the underlying output stream of this formatter.
     *
     * @throws java.io.IOException
     *             the stream's own flush method threw an exception.
     */
    public void flush() throws IOException {
        out.flush();
    }

    /**
     * {@inheritDoc}
     * <p>
     * Release the internal ObjectReader state.
     *
     * @since 4.0
     */
    @Override
    public void close() {
        if (reader != null && closeReader) {
            reader.close();
        }
    }

    /**
     * Determine the differences between two trees.
     *
     * No output is created, instead only the file paths that are different are
     * returned. Callers may choose to format these paths themselves, or convert
     * them into {@link org.eclipse.jgit.patch.FileHeader} instances with a
     * complete edit list by calling {@link #toFileHeader(DiffEntry)}.
     * <p>
     * Either side may be null to indicate that the tree has beed added or
     * removed. The diff will be computed against nothing.
     *
     * @param a
     *            the old (or previous) side or null
     * @param b
     *            the new (or updated) side or null
     * @return the paths that are different.
     * @throws java.io.IOException
     *             trees cannot be read or file contents cannot be read.
     */
    public List<DiffEntry> scan(AnyObjectId a, AnyObjectId b) throws IOException {
        assertHaveReader();

        try (RevWalk rw = new RevWalk(reader)) {
            RevTree aTree = a != null ? rw.parseTree(a) : null;
            RevTree bTree = b != null ? rw.parseTree(b) : null;
            return scan(aTree, bTree);
        }
    }

    /**
     * Determine the differences between two trees.
     *
     * No output is created, instead only the file paths that are different are
     * returned. Callers may choose to format these paths themselves, or convert
     * them into {@link org.eclipse.jgit.patch.FileHeader} instances with a
     * complete edit list by calling {@link #toFileHeader(DiffEntry)}.
     * <p>
     * Either side may be null to indicate that the tree has beed added or
     * removed. The diff will be computed against nothing.
     *
     * @param a
     *            the old (or previous) side or null
     * @param b
     *            the new (or updated) side or null
     * @return the paths that are different.
     * @throws java.io.IOException
     *             trees cannot be read or file contents cannot be read.
     */
    public List<DiffEntry> scan(RevTree a, RevTree b) throws IOException {
        assertHaveReader();

        AbstractTreeIterator aIterator = makeIteratorFromTreeOrNull(a);
        AbstractTreeIterator bIterator = makeIteratorFromTreeOrNull(b);
        return scan(aIterator, bIterator);
    }

    private AbstractTreeIterator makeIteratorFromTreeOrNull(RevTree tree)
            throws IncorrectObjectTypeException, IOException {
        if (tree != null) {
            CanonicalTreeParser parser = new CanonicalTreeParser();
            parser.reset(reader, tree);
            return parser;
        }
        return new EmptyTreeIterator();
    }

    /**
     * Determine the differences between two trees.
     *
     * No output is created, instead only the file paths that are different are
     * returned. Callers may choose to format these paths themselves, or convert
     * them into {@link org.eclipse.jgit.patch.FileHeader} instances with a
     * complete edit list by calling {@link #toFileHeader(DiffEntry)}.
     *
     * @param a
     *            the old (or previous) side.
     * @param b
     *            the new (or updated) side.
     * @return the paths that are different.
     * @throws java.io.IOException
     *             trees cannot be read or file contents cannot be read.
     */
    public List<DiffEntry> scan(AbstractTreeIterator a, AbstractTreeIterator b) throws IOException {
        assertHaveReader();

        TreeWalk walk = new TreeWalk(reader);
        walk.addTree(a);
        walk.addTree(b);
        walk.setRecursive(true);

        TreeFilter filter = getDiffTreeFilterFor(a, b);
        if (pathFilter instanceof FollowFilter) {
            walk.setFilter(AndTreeFilter.create(PathFilter.create(((FollowFilter) pathFilter).getPath()), filter));
        } else {
            walk.setFilter(AndTreeFilter.create(pathFilter, filter));
        }

        source = new ContentSource.Pair(source(a), source(b));

        List<DiffEntry> files = DiffEntry.scan(walk);
        if (pathFilter instanceof FollowFilter && isAdd(files)) {
            // The file we are following was added here, find where it
            // came from so we can properly show the rename or copy,
            // then continue digging backwards.
            //
            a.reset();
            b.reset();
            walk.reset();
            walk.addTree(a);
            walk.addTree(b);
            walk.setFilter(filter);

            if (renameDetector == null)
                setDetectRenames(true);
            files = updateFollowFilter(detectRenames(DiffEntry.scan(walk)));

        } else if (renameDetector != null)
            files = detectRenames(files);

        return files;
    }

    private static TreeFilter getDiffTreeFilterFor(AbstractTreeIterator a, AbstractTreeIterator b) {
        if (a instanceof DirCacheIterator && b instanceof WorkingTreeIterator)
            return new IndexDiffFilter(0, 1);

        if (a instanceof WorkingTreeIterator && b instanceof DirCacheIterator)
            return new IndexDiffFilter(1, 0);

        TreeFilter filter = TreeFilter.ANY_DIFF;
        if (a instanceof WorkingTreeIterator)
            filter = AndTreeFilter.create(new NotIgnoredFilter(0), filter);
        if (b instanceof WorkingTreeIterator)
            filter = AndTreeFilter.create(new NotIgnoredFilter(1), filter);
        return filter;
    }

    private ContentSource source(AbstractTreeIterator iterator) {
        if (iterator instanceof WorkingTreeIterator)
            return ContentSource.create((WorkingTreeIterator) iterator);
        return ContentSource.create(reader);
    }

    private List<DiffEntry> detectRenames(List<DiffEntry> files) throws IOException {
        renameDetector.reset();
        renameDetector.addAll(files);
        try {
            return renameDetector.compute(reader, progressMonitor);
        } catch (CancelledException e) {
            // TODO: consider propagating once bug 536323 is tackled
            // (making DiffEntry.scan() and DiffFormatter.scan() and
            // format() cancellable).
            return Collections.emptyList();
        }
    }

    private boolean isAdd(List<DiffEntry> files) {
        String oldPath = ((FollowFilter) pathFilter).getPath();
        for (DiffEntry ent : files) {
            if (ent.getChangeType() == ADD && ent.getNewPath().equals(oldPath))
                return true;
        }
        return false;
    }

    private List<DiffEntry> updateFollowFilter(List<DiffEntry> files) {
        String oldPath = ((FollowFilter) pathFilter).getPath();
        for (DiffEntry ent : files) {
            if (isRename(ent) && ent.getNewPath().equals(oldPath)) {
                pathFilter = FollowFilter.create(ent.getOldPath(), diffCfg);
                return Collections.singletonList(ent);
            }
        }
        return Collections.emptyList();
    }

    private static boolean isRename(DiffEntry ent) {
        return ent.getChangeType() == RENAME || ent.getChangeType() == COPY;
    }

    /**
     * Format the differences between two trees.
     *
     * The patch is expressed as instructions to modify {@code a} to make it
     * {@code b}.
     * <p>
     * Either side may be null to indicate that the tree has beed added or
     * removed. The diff will be computed against nothing.
     *
     * @param a
     *            the old (or previous) side or null
     * @param b
     *            the new (or updated) side or null
     * @throws java.io.IOException
     *             trees cannot be read, file contents cannot be read, or the
     *             patch cannot be output.
     */
    public void format(AnyObjectId a, AnyObjectId b) throws IOException {
        format(scan(a, b));
    }

    /**
     * Format the differences between two trees.
     *
     * The patch is expressed as instructions to modify {@code a} to make it
     * {@code b}.
     *
     * <p>
     * Either side may be null to indicate that the tree has beed added or
     * removed. The diff will be computed against nothing.
     *
     * @param a
     *            the old (or previous) side or null
     * @param b
     *            the new (or updated) side or null
     * @throws java.io.IOException
     *             trees cannot be read, file contents cannot be read, or the
     *             patch cannot be output.
     */
    public void format(RevTree a, RevTree b) throws IOException {
        format(scan(a, b));
    }

    /**
     * Format the differences between two trees.
     *
     * The patch is expressed as instructions to modify {@code a} to make it
     * {@code b}.
     * <p>
     * Either side may be null to indicate that the tree has beed added or
     * removed. The diff will be computed against nothing.
     *
     * @param a
     *            the old (or previous) side or null
     * @param b
     *            the new (or updated) side or null
     * @throws java.io.IOException
     *             trees cannot be read, file contents cannot be read, or the
     *             patch cannot be output.
     */
    public void format(AbstractTreeIterator a, AbstractTreeIterator b) throws IOException {
        format(scan(a, b));
    }

    /**
     * Format a patch script from a list of difference entries. Requires
     * {@link #scan(AbstractTreeIterator, AbstractTreeIterator)} to have been
     * called first.
     *
     * @param entries
     *            entries describing the affected files.
     * @throws java.io.IOException
     *             a file's content cannot be read, or the output stream cannot
     *             be written to.
     */
    public void format(List<? extends DiffEntry> entries) throws IOException {
        for (DiffEntry ent : entries)
            format(ent);
    }

    /**
     * Format a patch script for one file entry.
     *
     * @param ent
     *            the entry to be formatted.
     * @throws java.io.IOException
     *             a file's content cannot be read, or the output stream cannot
     *             be written to.
     */
    public void format(DiffEntry ent) throws IOException {
        FormatResult res = createFormatResult(ent);
        format(res.header, res.a, res.b);
    }

    private static byte[] writeGitLinkText(AbbreviatedObjectId id) {
        if (ObjectId.zeroId().equals(id.toObjectId())) {
            return EMPTY;
        }
        return encodeASCII("Subproject commit " + id.name() //$NON-NLS-1$
                + "\n"); //$NON-NLS-1$
    }

    private String format(AbbreviatedObjectId id) {
        if (id.isComplete() && reader != null) {
            try {
                id = reader.abbreviate(id.toObjectId(), abbreviationLength);
            } catch (IOException cannotAbbreviate) {
                // Ignore this. We'll report the full identity.
            }
        }
        return id.name();
    }

    private String quotePath(String path) {
        if (quotePaths == null || quotePaths.booleanValue()) {
            return QuotedString.GIT_PATH.quote(path);
        }
        return QuotedString.GIT_PATH_MINIMAL.quote(path);
    }

    /**
     * Format a patch script, reusing a previously parsed FileHeader.
     * <p>
     * This formatter is primarily useful for editing an existing patch script
     * to increase or reduce the number of lines of context within the script.
     * All header lines are reused as-is from the supplied FileHeader.
     *
     * @param head
     *            existing file header containing the header lines to copy.
     * @param a
     *            text source for the pre-image version of the content. This
     *            must match the content of
     *            {@link org.eclipse.jgit.patch.FileHeader#getOldId()}.
     * @param b
     *            text source for the post-image version of the content. This
     *            must match the content of
     *            {@link org.eclipse.jgit.patch.FileHeader#getNewId()}.
     * @throws java.io.IOException
     *             writing to the supplied stream failed.
     */
    public void format(FileHeader head, RawText a, RawText b) throws IOException {
        // Reuse the existing FileHeader as-is by blindly copying its
        // header lines, but avoiding its hunks. Instead we recreate
        // the hunks from the text instances we have been supplied.
        //
        final int start = head.getStartOffset();
        int end = head.getEndOffset();
        if (!head.getHunks().isEmpty())
            end = head.getHunks().get(0).getStartOffset();
        out.write(head.getBuffer(), start, end - start);
        if (head.getPatchType() == PatchType.UNIFIED)
            format(head.toEditList(), a, b);
    }

    /**
     * Formats a list of edits in unified diff format
     *
     * @param edits
     *            some differences which have been calculated between A and B
     * @param a
     *            the text A which was compared
     * @param b
     *            the text B which was compared
     * @throws java.io.IOException
     */
    public void format(EditList edits, RawText a, RawText b) throws IOException {
        for (int curIdx = 0; curIdx < edits.size();) {
            Edit curEdit = edits.get(curIdx);
            final int endIdx = findCombinedEnd(edits, curIdx);
            final Edit endEdit = edits.get(endIdx);

            int aCur = (int) Math.max(0, (long) curEdit.getBeginA() - context);
            int bCur = (int) Math.max(0, (long) curEdit.getBeginB() - context);
            final int aEnd = (int) Math.min(a.size(), (long) endEdit.getEndA() + context);
            final int bEnd = (int) Math.min(b.size(), (long) endEdit.getEndB() + context);

            writeHunkHeader(aCur, aEnd, bCur, bEnd);

            while (aCur < aEnd || bCur < bEnd) {
                if (aCur < curEdit.getBeginA() || endIdx + 1 < curIdx) {
                    writeContextLine(a, aCur);
                    if (isEndOfLineMissing(a, aCur))
                        out.write(noNewLine);
                    aCur++;
                    bCur++;
                } else if (aCur < curEdit.getEndA()) {
                    writeRemovedLine(a, aCur);
                    if (isEndOfLineMissing(a, aCur))
                        out.write(noNewLine);
                    aCur++;
                } else if (bCur < curEdit.getEndB()) {
                    writeAddedLine(b, bCur);
                    if (isEndOfLineMissing(b, bCur))
                        out.write(noNewLine);
                    bCur++;
                }

                if (end(curEdit, aCur, bCur) && ++curIdx < edits.size())
                    curEdit = edits.get(curIdx);
            }
        }
    }

    /**
     * Output a line of context (unmodified line).
     *
     * @param text
     *            RawText for accessing raw data
     * @param line
     *            the line number within text
     * @throws java.io.IOException
     */
    protected void writeContextLine(RawText text, int line) throws IOException {
        writeLine(' ', text, line);
    }

    private static boolean isEndOfLineMissing(RawText text, int line) {
        return line + 1 == text.size() && text.isMissingNewlineAtEnd();
    }

    /**
     * Output an added line.
     *
     * @param text
     *            RawText for accessing raw data
     * @param line
     *            the line number within text
     * @throws java.io.IOException
     */
    protected void writeAddedLine(RawText text, int line) throws IOException {
        writeLine('+', text, line);
    }

    /**
     * Output a removed line
     *
     * @param text
     *            RawText for accessing raw data
     * @param line
     *            the line number within text
     * @throws java.io.IOException
     */
    protected void writeRemovedLine(RawText text, int line) throws IOException {
        writeLine('-', text, line);
    }

    /**
     * Output a hunk header
     *
     * @param aStartLine
     *            within first source
     * @param aEndLine
     *            within first source
     * @param bStartLine
     *            within second source
     * @param bEndLine
     *            within second source
     * @throws java.io.IOException
     */
    protected void writeHunkHeader(int aStartLine, int aEndLine, int bStartLine, int bEndLine) throws IOException {
        out.write('@');
        out.write('@');
        writeRange('-', aStartLine + 1, aEndLine - aStartLine);
        writeRange('+', bStartLine + 1, bEndLine - bStartLine);
        out.write(' ');
        out.write('@');
        out.write('@');
        out.write('\n');
    }

    private void writeRange(char prefix, int begin, int cnt) throws IOException {
        out.write(' ');
        out.write(prefix);
        switch (cnt) {
        case 0:
            // If the range is empty, its beginning number must be the
            // line just before the range, or 0 if the range is at the
            // start of the file stream. Here, begin is always 1 based,
            // so an empty file would produce "0,0".
            //
            out.write(encodeASCII(begin - 1));
            out.write(',');
            out.write('0');
            break;

        case 1:
            // If the range is exactly one line, produce only the number.
            //
            out.write(encodeASCII(begin));
            break;

        default:
            out.write(encodeASCII(begin));
            out.write(',');
            out.write(encodeASCII(cnt));
            break;
        }
    }

    /**
     * Write a standard patch script line.
     *
     * @param prefix
     *            prefix before the line, typically '-', '+', ' '.
     * @param text
     *            the text object to obtain the line from.
     * @param cur
     *            line number to output.
     * @throws java.io.IOException
     *             the stream threw an exception while writing to it.
     */
    protected void writeLine(final char prefix, final RawText text, final int cur) throws IOException {
        out.write(prefix);
        text.writeLine(out, cur);
        out.write('\n');
    }

    /**
     * Creates a {@link org.eclipse.jgit.patch.FileHeader} representing the
     * given {@link org.eclipse.jgit.diff.DiffEntry}
     * <p>
     * This method does not use the OutputStream associated with this
     * DiffFormatter instance. It is therefore safe to instantiate this
     * DiffFormatter instance with a
     * {@link org.eclipse.jgit.util.io.DisabledOutputStream} if this method is
     * the only one that will be used.
     *
     * @param ent
     *            the DiffEntry to create the FileHeader for
     * @return a FileHeader representing the DiffEntry. The FileHeader's buffer
     *         will contain only the header of the diff output. It will also
     *         contain one {@link org.eclipse.jgit.patch.HunkHeader}.
     * @throws java.io.IOException
     *             the stream threw an exception while writing to it, or one of
     *             the blobs referenced by the DiffEntry could not be read.
     * @throws org.eclipse.jgit.errors.CorruptObjectException
     *             one of the blobs referenced by the DiffEntry is corrupt.
     * @throws org.eclipse.jgit.errors.MissingObjectException
     *             one of the blobs referenced by the DiffEntry is missing.
     */
    public FileHeader toFileHeader(DiffEntry ent)
            throws IOException, CorruptObjectException, MissingObjectException {
        return createFormatResult(ent).header;
    }

    private static class FormatResult {
        FileHeader header;

        RawText a;

        RawText b;
    }

    private FormatResult createFormatResult(DiffEntry ent)
            throws IOException, CorruptObjectException, MissingObjectException {
        final FormatResult res = new FormatResult();
        ByteArrayOutputStream buf = new ByteArrayOutputStream();
        final EditList editList;
        final FileHeader.PatchType type;

        formatHeader(buf, ent);

        if (ent.getOldId() == null || ent.getNewId() == null) {
            // Content not changed (e.g. only mode, pure rename)
            editList = new EditList();
            type = PatchType.UNIFIED;
            res.header = new FileHeader(buf.toByteArray(), editList, type);
            return res;
        }

        assertHaveReader();

        RawText aRaw = null;
        RawText bRaw = null;
        if (ent.getOldMode() == GITLINK || ent.getNewMode() == GITLINK) {
            aRaw = new RawText(writeGitLinkText(ent.getOldId()));
            bRaw = new RawText(writeGitLinkText(ent.getNewId()));
        } else {
            try {
                aRaw = open(OLD, ent);
                bRaw = open(NEW, ent);
            } catch (BinaryBlobException e) {
                // Do nothing; we check for null below.
                formatOldNewPaths(buf, ent);
                buf.write(encodeASCII("Binary files differ\n")); //$NON-NLS-1$
                editList = new EditList();
                type = PatchType.BINARY;
                res.header = new FileHeader(buf.toByteArray(), editList, type);
                return res;
            }
        }

        res.a = aRaw;
        res.b = bRaw;
        editList = diff(res.a, res.b);
        type = PatchType.UNIFIED;

        switch (ent.getChangeType()) {
        case RENAME:
        case COPY:
            if (!editList.isEmpty())
                formatOldNewPaths(buf, ent);
            break;

        default:
            formatOldNewPaths(buf, ent);
            break;
        }

        res.header = new FileHeader(buf.toByteArray(), editList, type);
        return res;
    }

    private EditList diff(RawText a, RawText b) {
        return diffAlgorithm.diff(comparator, a, b);
    }

    private void assertHaveReader() {
        if (reader == null) {
            throw new IllegalStateException(JGitText.get().readerIsRequired);
        }
    }

    private RawText open(DiffEntry.Side side, DiffEntry entry) throws IOException, BinaryBlobException {
        if (entry.getMode(side) == FileMode.MISSING)
            return RawText.EMPTY_TEXT;

        if (entry.getMode(side).getObjectType() != Constants.OBJ_BLOB)
            return RawText.EMPTY_TEXT;

        AbbreviatedObjectId id = entry.getId(side);
        if (!id.isComplete()) {
            Collection<ObjectId> ids = reader.resolve(id);
            if (ids.size() == 1) {
                id = AbbreviatedObjectId.fromObjectId(ids.iterator().next());
                switch (side) {
                case OLD:
                    entry.oldId = id;
                    break;
                case NEW:
                    entry.newId = id;
                    break;
                }
            } else if (ids.isEmpty())
                throw new MissingObjectException(id, Constants.OBJ_BLOB);
            else
                throw new AmbiguousObjectException(id, ids);
        }

        ObjectLoader ldr = LfsFactory.getInstance().applySmudgeFilter(repository, source.open(side, entry),
                entry.getDiffAttribute());
        return RawText.load(ldr, binaryFileThreshold);
    }

    /**
     * Output the first header line
     *
     * @param o
     *            The stream the formatter will write the first header line to
     * @param type
     *            The {@link org.eclipse.jgit.diff.DiffEntry.ChangeType}
     * @param oldPath
     *            old path to the file
     * @param newPath
     *            new path to the file
     * @throws java.io.IOException
     *             the stream threw an exception while writing to it.
     */
    protected void formatGitDiffFirstHeaderLine(ByteArrayOutputStream o, final ChangeType type,
            final String oldPath, final String newPath) throws IOException {
        o.write(encodeASCII("diff --git ")); //$NON-NLS-1$
        o.write(encode(quotePath(oldPrefix + (type == ADD ? newPath : oldPath))));
        o.write(' ');
        o.write(encode(quotePath(newPrefix + (type == DELETE ? oldPath : newPath))));
        o.write('\n');
    }

    private void formatHeader(ByteArrayOutputStream o, DiffEntry ent) throws IOException {
        final ChangeType type = ent.getChangeType();
        final String oldp = ent.getOldPath();
        final String newp = ent.getNewPath();
        final FileMode oldMode = ent.getOldMode();
        final FileMode newMode = ent.getNewMode();

        formatGitDiffFirstHeaderLine(o, type, oldp, newp);

        if ((type == MODIFY || type == COPY || type == RENAME) && !oldMode.equals(newMode)) {
            o.write(encodeASCII("old mode ")); //$NON-NLS-1$
            oldMode.copyTo(o);
            o.write('\n');

            o.write(encodeASCII("new mode ")); //$NON-NLS-1$
            newMode.copyTo(o);
            o.write('\n');
        }

        switch (type) {
        case ADD:
            o.write(encodeASCII("new file mode ")); //$NON-NLS-1$
            newMode.copyTo(o);
            o.write('\n');
            break;

        case DELETE:
            o.write(encodeASCII("deleted file mode ")); //$NON-NLS-1$
            oldMode.copyTo(o);
            o.write('\n');
            break;

        case RENAME:
            o.write(encodeASCII("similarity index " + ent.getScore() + "%")); //$NON-NLS-1$ //$NON-NLS-2$
            o.write('\n');

            o.write(encode("rename from " + quotePath(oldp))); //$NON-NLS-1$
            o.write('\n');

            o.write(encode("rename to " + quotePath(newp))); //$NON-NLS-1$
            o.write('\n');
            break;

        case COPY:
            o.write(encodeASCII("similarity index " + ent.getScore() + "%")); //$NON-NLS-1$ //$NON-NLS-2$
            o.write('\n');

            o.write(encode("copy from " + quotePath(oldp))); //$NON-NLS-1$
            o.write('\n');

            o.write(encode("copy to " + quotePath(newp))); //$NON-NLS-1$
            o.write('\n');
            break;

        case MODIFY:
            if (0 < ent.getScore()) {
                o.write(encodeASCII("dissimilarity index " //$NON-NLS-1$
                        + (100 - ent.getScore()) + "%")); //$NON-NLS-1$
                o.write('\n');
            }
            break;
        }

        if (ent.getOldId() != null && !ent.getOldId().equals(ent.getNewId())) {
            formatIndexLine(o, ent);
        }
    }

    /**
     * Format index line
     *
     * @param o
     *            the stream the formatter will write line data to
     * @param ent
     *            the DiffEntry to create the FileHeader for
     * @throws java.io.IOException
     *             writing to the supplied stream failed.
     */
    protected void formatIndexLine(OutputStream o, DiffEntry ent) throws IOException {
        o.write(encodeASCII("index " // //$NON-NLS-1$
                + format(ent.getOldId()) //
                + ".." // //$NON-NLS-1$
                + format(ent.getNewId())));
        if (ent.getOldMode().equals(ent.getNewMode())) {
            o.write(' ');
            ent.getNewMode().copyTo(o);
        }
        o.write('\n');
    }

    private void formatOldNewPaths(ByteArrayOutputStream o, DiffEntry ent) throws IOException {
        if (ent.oldId.equals(ent.newId))
            return;

        final String oldp;
        final String newp;

        switch (ent.getChangeType()) {
        case ADD:
            oldp = DiffEntry.DEV_NULL;
            newp = quotePath(newPrefix + ent.getNewPath());
            break;

        case DELETE:
            oldp = quotePath(oldPrefix + ent.getOldPath());
            newp = DiffEntry.DEV_NULL;
            break;

        default:
            oldp = quotePath(oldPrefix + ent.getOldPath());
            newp = quotePath(newPrefix + ent.getNewPath());
            break;
        }

        o.write(encode("--- " + oldp + "\n")); //$NON-NLS-1$ //$NON-NLS-2$
        o.write(encode("+++ " + newp + "\n")); //$NON-NLS-1$ //$NON-NLS-2$
    }

    private int findCombinedEnd(List<Edit> edits, int i) {
        int end = i + 1;
        while (end < edits.size() && (combineA(edits, end) || combineB(edits, end)))
            end++;
        return end - 1;
    }

    private boolean combineA(List<Edit> e, int i) {
        return e.get(i).getBeginA() - e.get(i - 1).getEndA() <= 2 * context;
    }

    private boolean combineB(List<Edit> e, int i) {
        return e.get(i).getBeginB() - e.get(i - 1).getEndB() <= 2 * context;
    }

    private static boolean end(Edit edit, int a, int b) {
        return edit.getEndA() <= a && edit.getEndB() <= b;
    }
}