#!/usr/bin/perl -w

# Copyright (C) 2007, 2008, 2009 Apple Inc.  All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# 1.  Redistributions of source code must retain the above copyright
#     notice, this list of conditions and the following disclaimer. 
# 2.  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. 
# 3.  Neither the name of Apple Computer, Inc. ("Apple") 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 APPLE AND ITS 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 APPLE OR ITS 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.

# Merge and resolve ChangeLog conflicts for svn and git repositories

use strict;

use FindBin;
use lib $FindBin::Bin;

use File::Basename;
use File::Copy;
use File::Path;
use File::Spec;
use Getopt::Long;
use POSIX;
use VCSUtils;

sub canonicalRelativePath($);
sub conflictFiles($);
sub findChangeLog($);
sub findUnmergedChangeLogs();
sub fixMergedChangeLogs($;@);
sub fixOneMergedChangeLog($);
sub hasGitUnmergedFiles();
sub isInGitFilterBranch();
sub mergeChanges($$$);
sub parseFixMerged($$;$);
sub removeChangeLogArguments($);
sub resolveChangeLog($);
sub resolveConflict($);
sub showStatus($;$);
sub usageAndExit();

my $isGit = isGit();
my $isSVN = isSVN();

my $SVN = "svn";
my $GIT = "git";

my $fixMerged;
my $gitRebaseContinue = 0;
my $mergeDriver = 0;
my $printWarnings = 1;
my $showHelp;

my $getOptionsResult = GetOptions(
    'c|continue!'     => \$gitRebaseContinue,
    'f|fix-merged:s'  => \&parseFixMerged,
    'm|merge-driver!' => \$mergeDriver,
    'h|help'          => \$showHelp,
    'w|warnings!'     => \$printWarnings,
);

my $relativePath = isInGitFilterBranch() ? '.' : chdirReturningRelativePath(determineVCSRoot());

my @changeLogFiles = removeChangeLogArguments($relativePath);

if (!defined $fixMerged && !$mergeDriver && scalar(@changeLogFiles) == 0) {
    @changeLogFiles = findUnmergedChangeLogs();
}

if (!$mergeDriver && scalar(@ARGV) > 0) {
    print STDERR "ERROR: Files listed on command-line that are not ChangeLogs.\n";
    undef $getOptionsResult;
} elsif (!defined $fixMerged && !$mergeDriver && scalar(@changeLogFiles) == 0) {
    print STDERR "ERROR: No ChangeLog files listed on command-line or found unmerged.\n";
    undef $getOptionsResult;
} elsif ($gitRebaseContinue && !$isGit) {
    print STDERR "ERROR: --continue may only be used with a git repository\n";
    undef $getOptionsResult;
} elsif (defined $fixMerged && !$isGit) {
    print STDERR "ERROR: --fix-merged may only be used with a git repository\n";
    undef $getOptionsResult;
} elsif ($mergeDriver && !$isGit) {
    print STDERR "ERROR: --merge-driver may only be used with a git repository\n";
    undef $getOptionsResult;
} elsif ($mergeDriver && scalar(@ARGV) < 3) {
    print STDERR "ERROR: --merge-driver expects %O %A %B as arguments\n";
    undef $getOptionsResult;
}

sub usageAndExit()
{
    print STDERR <<__END__;
Usage: @{[ basename($0) ]} [options] [path/to/ChangeLog] [path/to/another/ChangeLog ...]
  -c|--[no-]continue               run "git rebase --continue" after fixing ChangeLog
                                   entries (default: --no-continue)
  -f|--fix-merged [revision-range] fix git-merged ChangeLog entries; if a revision-range
                                   is specified, run git filter-branch on the range
  -m|--merge-driver %O %A %B       act as a git merge-driver on files %O %A %B
  -h|--help                        show this help message
  -w|--[no-]warnings               show or suppress warnings (default: show warnings)
__END__
    exit 1;
}

if (!$getOptionsResult || $showHelp) {
    usageAndExit();
}

if (defined $fixMerged && length($fixMerged) > 0) {
    my $commitRange = $fixMerged;
    $commitRange = $commitRange . "..HEAD" if index($commitRange, "..") < 0;
    fixMergedChangeLogs($commitRange, @changeLogFiles);
} elsif ($mergeDriver) {
    my ($base, $theirs, $ours) = @ARGV;
    if (mergeChanges($ours, $base, $theirs)) {
        unlink($ours);
        copy($theirs, $ours) or die $!;
    } else {
        exit 1;
    }
} elsif (@changeLogFiles) {
    for my $file (@changeLogFiles) {
        if (defined $fixMerged) {
            fixOneMergedChangeLog($file);
        } else {
            resolveChangeLog($file);
        }
    }
} else {
    print STDERR "ERROR: Unknown combination of switches and arguments.\n";
    usageAndExit();
}

if ($gitRebaseContinue) {
    if (hasGitUnmergedFiles()) {
        print "Unmerged files; skipping '$GIT rebase --continue'.\n";
    } else {
        print "Running '$GIT rebase --continue'...\n";
        print `$GIT rebase --continue`;
    }
}

exit 0;

sub canonicalRelativePath($)
{
    my ($originalPath) = @_;
    my $absolutePath = Cwd::abs_path($originalPath);
    return File::Spec->abs2rel($absolutePath, Cwd::getcwd());
}

sub conflictFiles($)
{
    my ($file) = @_;
    my $fileMine;
    my $fileOlder;
    my $fileNewer;

    if (-e $file && -e "$file.orig" && -e "$file.rej") {
        return ("$file.rej", "$file.orig", $file);
    }

    if ($isSVN) {
        open STAT, "-|", $SVN, "status", $file or die $!;
        my $status = <STAT>;
        close STAT;
        if (!$status || $status !~ m/^C\s+/) {
            print STDERR "WARNING: ${file} is not in a conflicted state.\n" if $printWarnings;
            return ();
        }

        $fileMine = "${file}.mine" if -e "${file}.mine";

        my $currentRevision;
        open INFO, "-|", $SVN, "info", $file or die $!;
        while (my $line = <INFO>) {
            if ($line =~ m/^Revision: ([0-9]+)/) {
                $currentRevision = $1;
                { local $/ = undef; <INFO>; }  # Consume rest of input.
            }
        }
        close INFO;
        $fileNewer = "${file}.r${currentRevision}" if -e "${file}.r${currentRevision}";

        my @matchingFiles = grep { $_ ne $fileNewer } glob("${file}.r[0-9][0-9]*");
        if (scalar(@matchingFiles) > 1) {
            print STDERR "WARNING: Too many conflict files exist for ${file}!\n" if $printWarnings;
        } else {
            $fileOlder = shift @matchingFiles;
        }
    } elsif ($isGit) {
        my $gitPrefix = `$GIT rev-parse --show-prefix`;
        chomp $gitPrefix;
        open GIT, "-|", $GIT, "ls-files", "--unmerged", $file or die $!;
        while (my $line = <GIT>) {
            my ($mode, $hash, $stage, $fileName) = split(' ', $line);
            my $outputFile;
            if ($stage == 1) {
                $fileOlder = "${file}.BASE.$$";
                $outputFile = $fileOlder;
            } elsif ($stage == 2) {
                $fileNewer = "${file}.LOCAL.$$";
                $outputFile = $fileNewer;
            } elsif ($stage == 3) {
                $fileMine = "${file}.REMOTE.$$";
                $outputFile = $fileMine;
            } else {
                die "Unknown file stage: $stage";
            }
            system("$GIT cat-file blob :${stage}:${gitPrefix}${file} > $outputFile");
            die $! if WEXITSTATUS($?);
        }
        close GIT or die $!;
    } else {
        die "Unknown version control system";
    }

    if (!$fileMine && !$fileOlder && !$fileNewer) {
        print STDERR "WARNING: ${file} does not need merging.\n" if $printWarnings;
    } elsif (!$fileMine || !$fileOlder || !$fileNewer) {
        print STDERR "WARNING: ${file} is missing some conflict files.\n" if $printWarnings;
    }

    return ($fileMine, $fileOlder, $fileNewer);
}

sub findChangeLog($)
{
    return $_[0] if basename($_[0]) eq "ChangeLog";

    my $file = File::Spec->catfile($_[0], "ChangeLog");
    return $file if -d $_[0] and -e $file;

    return undef;
}

sub findUnmergedChangeLogs()
{
    my $statCommand = "";

    if ($isSVN) {
        $statCommand = "$SVN stat | grep '^C'";
    } elsif ($isGit) {
        $statCommand = "$GIT diff -r --name-status --diff-filter=U -C -C -M";
    } else {
        return ();
    }

    my @results = ();
    open STAT, "-|", $statCommand or die "The status failed: $!.\n";
    while (<STAT>) {
        if ($isSVN) {
            my $matches;
            my $file;
            if (isSVNVersion16OrNewer()) {
                $matches = /^([C]).{6} (.+?)[\r\n]*$/;
                $file = $2;
            } else {
                $matches = /^([C]).{5} (.+?)[\r\n]*$/;
                $file = $2;
            }
            if ($matches) {
                $file = findChangeLog(normalizePath($file));
                push @results, $file if $file;
            } else {
                print;  # error output from svn stat
            }
        } elsif ($isGit) {
            if (/^([U])\t(.+)$/) {
                my $file = findChangeLog(normalizePath($2));
                push @results, $file if $file;
            } else {
                print;  # error output from git diff
            }
        }
    }
    close STAT;

    return @results;
}

sub fixMergedChangeLogs($;@)
{
    my $revisionRange = shift;
    my @changedFiles = @_;

    if (scalar(@changedFiles) < 1) {
        # Read in list of files changed in $revisionRange
        open GIT, "-|", $GIT, "diff", "--name-only", $revisionRange or die $!;
        push @changedFiles, <GIT>;
        close GIT or die $!;
        die "No changed files in $revisionRange" if scalar(@changedFiles) < 1;
        chomp @changedFiles;
    }

    my @changeLogs = grep { defined $_ } map { findChangeLog($_) } @changedFiles;
    die "No changed ChangeLog files in $revisionRange" if scalar(@changeLogs) < 1;

    system("$GIT filter-branch --tree-filter 'PREVIOUS_COMMIT=\`$GIT rev-parse \$GIT_COMMIT^\` && MAPPED_PREVIOUS_COMMIT=\`map \$PREVIOUS_COMMIT\` \"$0\" -f \"" . join('" "', @changeLogs) . "\"' $revisionRange");

    # On success, remove the backup refs directory
    if (WEXITSTATUS($?) == 0) {
        rmtree(qw(.git/refs/original));
    }
}

sub fixOneMergedChangeLog($)
{
    my $file = shift;
    my $patch;

    # Read in patch for incorrectly merged ChangeLog entry
    {
        local $/ = undef;
        open GIT, "-|", $GIT, "diff", ($ENV{GIT_COMMIT} || "HEAD") . "^", $file or die $!;
        $patch = <GIT>;
        close GIT or die $!;
    }

    # Always checkout the previous commit's copy of the ChangeLog
    system($GIT, "checkout", $ENV{MAPPED_PREVIOUS_COMMIT} || "HEAD^", $file);
    die $! if WEXITSTATUS($?);

    # The patch must have 0 or more lines of context, then 1 or more lines
    # of additions, and then 1 or more lines of context.  If not, we skip it.
    if ($patch =~ /\n@@ -(\d+),(\d+) \+(\d+),(\d+) @@\n( .*\n)*((\+.*\n)+)( .*\n)+$/m) {
        # Copy the header from the original patch.
        my $newPatch = substr($patch, 0, index($patch, "@@ -${1},${2} +${3},${4} @@"));

        # Generate a new set of line numbers and patch lengths.  Our new
        # patch will start with the lines for the fixed ChangeLog entry,
        # then have 3 lines of context from the top of the current file to
        # make the patch apply cleanly.
        $newPatch .= "@@ -1,3 +1," . ($4 - $2 + 3) . " @@\n";

        # We assume that top few lines of the ChangeLog entry are actually
        # at the bottom of the list of added lines (due to the way the patch
        # algorithm works), so we simply search through the lines until we
        # find the date line, then move the rest of the lines to the top.
        my @patchLines = map { $_ . "\n" } split(/\n/, $6);
        foreach my $i (0 .. $#patchLines) {
            if ($patchLines[$i] =~ /^\+\d{4}-\d{2}-\d{2}  /) {
                unshift(@patchLines, splice(@patchLines, $i, scalar(@patchLines) - $i));
                last;
            }
        }

        $newPatch .= join("", @patchLines);

        # Add 3 lines of context to the end
        open FILE, "<", $file or die $!;
        for (my $i = 0; $i < 3; $i++) {
            $newPatch .= " " . <FILE>;
        }
        close FILE;

        # Apply the new patch
        open(PATCH, "| patch -p1 $file > " . File::Spec->devnull()) or die $!;
        print PATCH $newPatch;
        close(PATCH) or die $!;

        # Run "git add" on the fixed ChangeLog file
        system($GIT, "add", $file);
        die $! if WEXITSTATUS($?);

        showStatus($file, 1);
    } elsif ($patch) {
        # Restore the current copy of the ChangeLog file since we can't repatch it
        system($GIT, "checkout", $ENV{GIT_COMMIT} || "HEAD", $file);
        die $! if WEXITSTATUS($?);
        print STDERR "WARNING: Last change to ${file} could not be fixed and re-merged.\n" if $printWarnings;
    }
}

sub hasGitUnmergedFiles()
{
    my $output = `$GIT ls-files --unmerged`;
    return $output ne "";
}

sub isInGitFilterBranch()
{
    return exists $ENV{MAPPED_PREVIOUS_COMMIT} && $ENV{MAPPED_PREVIOUS_COMMIT};
}

sub mergeChanges($$$)
{
    my ($fileMine, $fileOlder, $fileNewer) = @_;

    my $traditionalReject = $fileMine =~ /\.rej$/ ? 1 : 0;

    local $/ = undef;

    my $patch;
    if ($traditionalReject) {
        open(DIFF, "<", $fileMine) or die $!;
        $patch = <DIFF>;
        close(DIFF);
        rename($fileMine, "$fileMine.save");
        rename($fileOlder, "$fileOlder.save");
    } else {
        open(DIFF, "-|", qw(diff -u -a --binary), $fileOlder, $fileMine) or die $!;
        $patch = <DIFF>;
        close(DIFF);
    }

    unlink("${fileNewer}.orig");
    unlink("${fileNewer}.rej");

    open(PATCH, "| patch --fuzz=3 --binary $fileNewer > " . File::Spec->devnull()) or die $!;
    print PATCH fixChangeLogPatch($patch);
    close(PATCH);

    my $result;

    # Refuse to merge the patch if it did not apply cleanly
    if (-e "${fileNewer}.rej") {
        unlink("${fileNewer}.rej");
        unlink($fileNewer);
        rename("${fileNewer}.orig", $fileNewer);
        $result = 0;
    } else {
        unlink("${fileNewer}.orig");
        $result = 1;
    }

    if ($traditionalReject) {
        rename("$fileMine.save", $fileMine);
        rename("$fileOlder.save", $fileOlder);
    }

    return $result;
}

sub parseFixMerged($$;$)
{
    my ($switchName, $key, $value) = @_;
    if (defined $key) {
        if (defined findChangeLog($key)) {
            unshift(@ARGV, $key);
            $fixMerged = "";
        } else {
            $fixMerged = $key;
        }
    } else {
        $fixMerged = "";
    }
}

sub removeChangeLogArguments($)
{
    my ($baseDir) = @_;
    my @results = ();

    for (my $i = 0; $i < scalar(@ARGV); ) {
        my $file = findChangeLog(canonicalRelativePath(File::Spec->catfile($baseDir, $ARGV[$i])));
        if (defined $file) {
            splice(@ARGV, $i, 1);
            push @results, $file;
        } else {
            $i++;
        }
    }

    return @results;
}

sub resolveChangeLog($)
{
    my ($file) = @_;

    my ($fileMine, $fileOlder, $fileNewer) = conflictFiles($file);

    return unless $fileMine && $fileOlder && $fileNewer;

    if (mergeChanges($fileMine, $fileOlder, $fileNewer)) {
        if ($file ne $fileNewer) {
            unlink($file);
            rename($fileNewer, $file) or die $!;
        }
        unlink($fileMine, $fileOlder);
        resolveConflict($file);
        showStatus($file, 1);
    } else {
        showStatus($file);
        print STDERR "WARNING: ${file} could not be merged using fuzz level 3.\n" if $printWarnings;
        unlink($fileMine, $fileOlder, $fileNewer) if $isGit;
    }
}

sub resolveConflict($)
{
    my ($file) = @_;

    if ($isSVN) {
        system($SVN, "resolved", $file);
        die $! if WEXITSTATUS($?);
    } elsif ($isGit) {
        system($GIT, "add", $file);
        die $! if WEXITSTATUS($?);
    } else {
        die "Unknown version control system";
    }
}

sub showStatus($;$)
{
    my ($file, $isConflictResolved) = @_;

    if ($isSVN) {
        system($SVN, "status", $file);
    } elsif ($isGit) {
        my @args = qw(--name-status);
        unshift @args, qw(--cached) if $isConflictResolved;
        system($GIT, "diff", @args, $file);
    } else {
        die "Unknown version control system";
    }
}