#!/usr/bin/perl -w

# Known limitations:
# - cannot add or remove binary files
# - does not propagate permissions
# - tells "ready for commit" even when things could not be completed
#   (eg addition of a binary file)

use strict;
use Getopt::Std;
use File::Temp qw(tempdir);
use Data::Dumper;
use File::Basename qw(basename dirname);

unless ($ENV{GIT_DIR} && -r $ENV{GIT_DIR}){
    die "GIT_DIR is not defined or is unreadable";
}

our ($opt_h, $opt_p, $opt_v, $opt_c, $opt_f, $opt_a, $opt_m );

getopts('hpvcfam:');

$opt_h && usage();

die "Need at least one commit identifier!" unless @ARGV;

# setup a tempdir
our ($tmpdir, $tmpdirname) = tempdir('git-cvsapplycommit-XXXXXX',
                                     TMPDIR => 1,
                                     CLEANUP => 1);

# resolve target commit
my $commit;
$commit = pop @ARGV;
$commit = safe_pipe_capture('git-rev-parse', '--verify', "$commit^0");
chomp $commit;
if ($?) {
    die "The commit reference $commit did not resolve!";
}

# resolve what parent we want
my $parent;
if (@ARGV) {
    $parent = pop @ARGV;
    $parent =  safe_pipe_capture('git-rev-parse', '--verify', "$parent^0");
    chomp $parent;
    if ($?) {
        die "The parent reference did not resolve!";
    }
}

# find parents from the commit itself
my @commit  = safe_pipe_capture('git-cat-file', 'commit', $commit);
my @parents;
my $committer;
my $author;
my $stage = 'headers'; # headers, msg
my $title;
my $msg = '';

foreach my $line (@commit) {
    chomp $line;
    if ($stage eq 'headers' && $line eq '') {
        $stage = 'msg';
        next;
    }

    if ($stage eq 'headers') {
        if ($line =~ m/^parent (\w{40})$/) { # found a parent
            push @parents, $1;
        } elsif ($line =~ m/^author (.+) \d+ \+\d+$/) {
            $author = $1;
        } elsif ($line =~ m/^committer (.+) \d+ \+\d+$/) {
            $committer = $1;
        }
    } else {
        $msg .= $line . "\n";
        unless ($title) {
            $title = $line;
        }
    }
}

if ($parent) {
    my $found;
    # double check that it's a valid parent
    foreach my $p (@parents) {
        if ($p eq $parent) {
            $found = 1;
            last;
        }; # found it
    }
    die "Did not find $parent in the parents for this commit!" if !$found;
} else { # we don't have a parent from the cmdline...
    if (@parents == 1) { # it's safe to get it from the commit
        $parent = $parents[0];
    } else { # or perhaps not!
        die "This commit has more than one parent -- please name the parent you want to use explicitly";
    }
}

$opt_v && print "Applying to CVS commit $commit from parent $parent\n";

# grab the commit message
open(MSG, ">.msg") or die "Cannot open .msg for writing";
if ($opt_m) {
    print MSG $opt_m;
}
print MSG $msg;
if ($opt_a) {
    print MSG "\n\nAuthor: $author\n";
    if ($author ne $committer) {
        print MSG "Committer: $committer\n";
    }
}
close MSG;

my (@afiles, @dfiles, @mfiles, @dirs);
my @files = safe_pipe_capture('git-diff-tree', '-r', $parent, $commit);
#print @files;
$? && die "Error in git-diff-tree";
foreach my $f (@files) {
    chomp $f;
    my @fields = split(m!\s+!, $f);
    if ($fields[4] eq 'A') {
        my $path = $fields[5];
        push @afiles, $path;
        # add any needed parent directories
        $path = dirname $path;
        while (!-d $path and ! grep { $_ eq $path } @dirs) {
            unshift @dirs, $path;
            $path = dirname $path;
        }
    }
    if ($fields[4] eq 'M') {
        push @mfiles, $fields[5];
    }
    if ($fields[4] eq 'D') {
        push @dfiles, $fields[5];
    }
}
$opt_v && print "The commit affects:\n ";
$opt_v && print join ("\n ", @afiles,@mfiles,@dfiles) . "\n\n";
undef @files; # don't need it anymore

# check that the files are clean and up to date according to cvs
my $dirty;
foreach my $d (@dirs) {
    if (-e $d) {
        $dirty = 1;
        warn "$d exists and is not a directory!\n";
    }
}
foreach my $f (@afiles) {
    # This should return only one value
    my @status = grep(m/^File/,  safe_pipe_capture('cvs', '-q', 'status' ,$f));
    if (@status > 1) { warn 'Strange! cvs status returned more than one line?'};
    if (-d dirname $f and $status[0] !~ m/Status: Unknown$/
        and $status[0] !~ m/^File: no file /) {
        $dirty = 1;
        warn "File $f is already known in your CVS checkout -- perhaps it has been added by another user. Or this may indicate that it exists on a different branch. If this is the case, use -f to force the merge.\n";
        warn "Status was: $status[0]\n";
    }
}
foreach my $f (@mfiles, @dfiles) {
    # TODO:we need to handle removed in cvs
    my @status = grep(m/^File/,  safe_pipe_capture('cvs', '-q', 'status' ,$f));
    if (@status > 1) { warn 'Strange! cvs status returned more than one line?'};
    unless ($status[0] =~ m/Status: Up-to-date$/) {
        $dirty = 1;
        warn "File $f not up to date in your CVS checkout!\n";
    }
}
if ($dirty) {
    if ($opt_f) {       warn "The tree is not clean -- forced merge\n";
        $dirty = 0;
    } else {
        die "Exiting: your CVS tree is not clean for this merge.";
    }
}

###
### NOTE: if you are planning to die() past this point
###       you MUST call cleanupcvs(@files) before die()
###


print "Creating new directories\n";
foreach my $d (@dirs) {
    unless (mkdir $d) {
        warn "Could not mkdir $d: $!";
        $dirty = 1;
    }
    `cvs add $d`;
    if ($?) {
        $dirty = 1;
        warn "Failed to cvs add directory $d -- you may need to do it manually";
    }
}

print "'Patching' binary files\n";

my @bfiles = grep(m/^Binary/, safe_pipe_capture('git-diff-tree', '-p', $parent, $commit));
@bfiles = map { chomp } @bfiles;
foreach my $f (@bfiles) {
    # check that the file in cvs matches the "old" file
    # extract the file to $tmpdir and compare with cmp
    my $tree = safe_pipe_capture('git-rev-parse', "$parent^{tree}");
    chomp $tree;
    my $blob = `git-ls-tree $tree "$f" | cut -f 1 | cut -d ' ' -f 3`;
    chomp $blob;
    `git-cat-file blob $blob > $tmpdir/blob`;
    if (system('cmp', '-s', $f, "$tmpdir/blob")) {
        warn "Binary file $f in CVS does not match parent.\n";
        $dirty = 1;
        next;
    }

    # replace with the new file
     `git-cat-file blob $blob > $f`;

    # TODO: something smart with file modes

}
if ($dirty) {
    cleanupcvs(@files);
    die "Exiting: Binary files in CVS do not match parent";
}

## apply non-binary changes
my $fuzz = $opt_p ? 0 : 2;

print "Patching non-binary files\n";
print `(git-diff-tree -p $parent -p $commit | patch -p1 -F $fuzz ) 2>&1`;

my $dirtypatch = 0;
if (($? >> 8) == 2) {
    cleanupcvs(@files);
    die "Exiting: Patch reported serious trouble -- you will have to apply this patch manually";
} elsif (($? >> 8) == 1) { # some hunks failed to apply
    $dirtypatch = 1;
}

foreach my $f (@afiles) {
    system('cvs', 'add', $f);
    if ($?) {
        $dirty = 1;
        warn "Failed to cvs add $f -- you may need to do it manually";
    }
}

foreach my $f (@dfiles) {
    system('cvs', 'rm', '-f', $f);
    if ($?) {
        $dirty = 1;
        warn "Failed to cvs rm -f $f -- you may need to do it manually";
    }
}

print "Commit to CVS\n";
print "Patch: $title\n";
my $commitfiles = join(' ', @afiles, @mfiles, @dfiles);
my $cmd = "cvs commit -F .msg $commitfiles";

if ($dirtypatch) {
    print "NOTE: One or more hunks failed to apply cleanly.\n";
    print "Resolve the conflicts and then commit using:\n";
    print "\n    $cmd\n\n";
    exit(1);
}


if ($opt_c) {
    print "Autocommit\n  $cmd\n";
    print safe_pipe_capture('cvs', 'commit', '-F', '.msg', @afiles, @mfiles, @dfiles);
    if ($?) {
        cleanupcvs(@files);
        die "Exiting: The commit did not succeed";
    }
    print "Committed successfully to CVS\n";
} else {
    print "Ready for you to commit, just run:\n\n   $cmd\n";
}
sub usage {
        print STDERR <<END;
Usage: GIT_DIR=/path/to/.git ${\basename $0} [-h] [-p] [-v] [-c] [-f] [-m msgprefix] [ parent ] commit
END
        exit(1);
}

# ensure cvs is clean before we die
sub cleanupcvs {
    my @files = @_;
    foreach my $f (@files) {
        system('cvs', '-q', 'update', '-C', $f);
        if ($?) {
            warn "Warning! Failed to cleanup state of $f\n";
        }
    }
}

# An alternative to `command` that allows input to be passed as an array
# to work around shell problems with weird characters in arguments
# if the exec returns non-zero we die
sub safe_pipe_capture {
    my @output;
    if (my $pid = open my $child, '-|') {
        @output = (<$child>);
        close $child or die join(' ',@_).": $! $?";
    } else {
        exec(@_) or die "$! $?"; # exec() can fail the executable can't be found
    }
    return wantarray ? @output : join('',@output);
}