#!/usr/bin/perl -w

# Copyright (C) 2007 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::Spec;
use Getopt::Long;
use VCSUtils;

sub conflictFiles($);
sub fixChangeLogPatch($);
sub mergeChanges($$$);
sub resolveConflict($);
sub showStatus($;$);

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

my $printWarnings = 1;
my $showHelp;

my $getOptionsResult = GetOptions(
    'h|help'         => \$showHelp,
    'w|warnings!'    => \$printWarnings,
);

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

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

    return undef;
}

my @changeLogFiles = grep { defined $_ } map { findChangeLog($_) } @ARGV;

if (scalar(@changeLogFiles) != scalar(@ARGV)) {
    print STDERR "ERROR: Files listed on command-line that are not ChangeLogs.\n";
    undef $getOptionsResult;
} elsif (scalar(@changeLogFiles) == 0) {
    print STDERR "ERROR: No ChangeLog files listed on command-line.\n";
    undef $getOptionsResult;
}

if (!$getOptionsResult || $showHelp) {
    print STDERR <<__END__;
Usage: @{[ basename($0) ]} [options] path/to/ChangeLog [path/to/another/ChangeLog ...]
  -h|--help           show this help message
  -w|--[no-]warnings  show or suppress warnings (default: show warnings)
__END__
    exit 1;
}

for my $file (@changeLogFiles) {
    my ($fileMine, $fileOlder, $fileNewer) = conflictFiles($file);
    if (!$fileMine || !$fileOlder || !$fileNewer) {
        next;
    }
    if (mergeChanges($fileMine, $fileOlder, $fileNewer)) {
        if ($file ne $fileNewer) {
            unlink($file);
            rename($fileNewer, $file) || die;
        }
        unlink($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();
    }
}

exit 0;

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 || 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 || die;
        while (my $line = <INFO>) {
            $currentRevision = $1 if $line =~ m/^Revision: ([0-9]+)/;
        }
        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 || 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");
        }
        close GIT;
    } 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 fixChangeLogPatch($)
{
    my $patch = shift;
    my $contextLineCount = 3;

    return $patch if $patch !~ /\n@@ -1,(\d+) \+1,(\d+) @@\n( .*\n)+(\+.*\n)+( .*\n){$contextLineCount}$/m;
    my ($oldLineCount, $newLineCount) = ($1, $2);
    return $patch if $oldLineCount <= $contextLineCount;

    # The diff(1) command is greedy when matching lines, so a new ChangeLog entry will
    # have lines of context at the top of a patch when the existing entry has the same
    # date and author as the new entry.  This nifty loop alters a ChangeLog patch so
    # that the added lines ("+") in the patch always start at the beginning of the
    # patch and there are no initial lines of context.
    my $newPatch;
    my $lineCountInState = 0;
    my $oldContentLineCountReduction = $oldLineCount - $contextLineCount;
    my $newContentLineCountWithoutContext = $newLineCount - $oldLineCount - $oldContentLineCountReduction;
    my ($stateHeader, $statePreContext, $stateNewChanges, $statePostContext) = (1..4);
    my $state = $stateHeader;
    foreach my $line (split(/\n/, $patch)) {
        $lineCountInState++;
        if ($state == $stateHeader && $line =~ /^@@ -1,$oldLineCount \+1,$newLineCount @\@$/) {
            $line = "@@ -1,$contextLineCount +1," . ($newLineCount - $oldContentLineCountReduction) . " @@";
            $lineCountInState = 0;
            $state = $statePreContext;
        } elsif ($state == $statePreContext && substr($line, 0, 1) eq " ") {
            $line = "+" . substr($line, 1);
            if ($lineCountInState == $oldContentLineCountReduction) {
                $lineCountInState = 0;
                $state = $stateNewChanges;
            }
        } elsif ($state == $stateNewChanges && substr($line, 0, 1) eq "+") {
            # No changes to these lines
            if ($lineCountInState == $newContentLineCountWithoutContext) {
                $lineCountInState = 0;
                $state = $statePostContext;
            }
        } elsif ($state == $statePostContext) {
            if (substr($line, 0, 1) eq "+" && $lineCountInState <= $oldContentLineCountReduction) {
                $line = " " . substr($line, 1);
            } elsif ($lineCountInState > $contextLineCount && substr($line, 0, 1) eq " ") {
                next; # Discard
            }
        }
        $newPatch .= $line . "\n";
    }

    return $newPatch;
}

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

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

    local $/ = undef;

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

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

    open(PATCH, "| patch --fuzz=3 $fileNewer > /dev/null") || die;
    print PATCH fixChangeLogPatch($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 resolveConflict($)
{
    my ($file) = @_;

    if (isSVN()) {
        system($SVN, "resolved", $file);
    } elsif (isGit()) {
        system($GIT, "add", $file);
    } 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";
    }
}