eval '(exit $?0)' && eval 'exec perl -wS "$0" "$@"'
  & eval 'exec perl -wS "$0" $argv:q'
    if 0;

use strict;
use POSIX qw(strftime);
use Getopt::Long qw(:config gnu_getopt no_ignore_case);
use Text::Wrap;
use Data::Dumper;
use threads;
use Thread::Queue;
use Time::ParseDate;
use Safe;
use Pod::Usage;
use Pod::Man;
use Pod::Find qw(pod_where);

my @append_files;
my $force;
my $verbose;
my $changelog_file = 'ChangeLog';
my $since_date;
my $until_date;
my $strip_cherry_pick;
my $amend_file;
my %amendment;
my $append_dot;

sub set_date {
    my ($time, $err) = parsedate($_[1], PREFER_PAST => 1, UK => 1);
    unless (defined($time)) {
	print STDERR "--$_[0]=$_[1]: $err\n";
	exit(1);
    }
    return strftime('%Y-%m-%d', localtime($time));
}

=head1 NAME

gencl - generate ChangeLog from git log output

=head1 SYNOPSIS

B<gencl>
[B<-fv>]    
[B<-a> I<FILE>]
[B<-F> I<FILE>]
[B<--amend=>I<FILE>]
[B<--append-dot>]
[B<--append=>I<FILE>]
[B<--file=>I<FILE>]
[B<--force>]
[B<--since=>I<DATE>]
[B<--strip-cherry-pick>]
[B<--until=>I<DATE>]    
[B<--verbose>]

B<gencl> B<-h> | B<--help> | B<--usage>

=head1 DESCRIPTION

Retrieves git log messages and reformats them as a valid ChangeLog
file.  The file begins with an automatically generated entry stating
the SHA1 hash of the git HEAD commit.  This entry is followed by
the log entries recreated from the git log, in reverse chronological
order.  By default, entire log is converted.  This can be changed by
using B<--since> and/or B<--until> options.  Files specified with the
B<--append> options (if any), are appended after the converted entries.
The file ends with the B<emacs> B<Local Variables> stanza.

If the B<ChangeLog> file exists, B<gencl> verifies if the source tree
has changed since the file was created.  The file is re-created only if
there were some changes (whether committed or not).  The the B<--force>
(B<-f>) option instructs B<gencl> to recreate the file unconditionally.

The file supplied with the B<--amend> option is used to correct spelling
(and other) errors in the log entries.  It consists of entries delimited
with one or more empty lines.  Each entry begins with a full SHA1 hash
of the commit it applies to.  The hash is followed by one or more lines
with a valid Perl code (typically, B<s///> statements).  Comments are
introduced with the B<#> sign.  For each git log entry, its hash is looked
up in that file.  If found, the B<$_> variable is set to the commit subject,
followed by the commit body and the code is evaluated.
        
=head1 OPTIONS

=over 4

=item B<-a>, B<--append=>I<FILE>

Append I<FILE> to the end of the generated file.  Multiple B<--append>
are processed in the order of their occurrence on the command line.
The content of I<FILE> is appended verbatim, except that the line beginning
with the text B<Local Variables:> is taken to mark the end of file.
   
=item B<-F>, B<--file=>I<FILE>

Create I<FILE> instead of the B<ChangeLog>.

=item B<-f>, B<--force>

Force recreating the ChangeLog, even if no new commits were added to the
repository since its creation.
    
=item B<-v>, B<--verbose>

Increase output verbosity.

=item B<--since=>I<DATE>

Convert only the logs since I<DATE>.  See B<Time::ParseDate>(3), for
a list of valid I<DATE> formats.

=item B<--until=>I<DATE>

Convert only the logs until I<DATE>.  See B<Time::ParseDate>(3), for
a list of valid I<DATE> formats.
    
=item B<--strip-cherry-pick>

Remove data inserted by B<git cherry-pick>.  This includes the "cherry picked
from commit ..." line, and the possible final "Conflicts:" paragraph.

=item B<--amend=>I<FILE>

Read amendment instructions from I<FILE>.

=item B<--append-dot>

Append a dot to the subject line of each commit message if there is no other
punctuation the end.     
    
=back

=head1 DIFFERENCES FROM GITLOG-TO-CHANGELOG

=over 4

=item 1

B<gencl> writes output to the disk file, whereas B<gitlog-to-changelog>
prints it to the standard output.

=item 2

The created B<ChangeLog> begins with an automatically generated entry and
ends with the B<Local Variables> stanza.

=item 3

The B<ChangeLog> file is re-created only if the source tree was changed
since it was written (whether these changes have been committed or not).

=item 4

Arbitrary number of files can be concatenated to the produced file.  This
is handy for projects that switched to B<git> from other VCS.

=item 5

Each entry is reformatted using B<Text::Wrap>.

=item 6

The following B<gitlab-to-changelog> options are not implemented: B<--cluster>,
B<--ignore-matching>, B<--ignore_line>.
    
=back
    
=cut    
    
sub pod_usage_msg {
    my ($obj) = @_;
    open my $fd, '>', \my $msg;

    pod2usage(-verbose => 99,
              -sections => 'NAME',
              -output => $fd,
              -exitval => 'NOEXIT');
    my @a = split /\n/, $msg;
    $msg = $a[1];
    $msg =~ s/^\s+//;
    $msg =~ s/ - /: /;
    return $msg;
}

GetOptions(
    'h' => sub {
	pod2usage(-message => pod_usage_msg(),
		  -exitstatus => 0,
		  -input => pod_where({-inc => 1}, $0))
    },
    'help' => sub {
	pod2usage(-exitstatus => 0,
		  -verbose => 2,
		  -input => pod_where({-inc => 1}, $0));
    },
    'usage' => sub {
	pod2usage(-exitstatus => 0,
                  -verbose => 0,
                  -input => pod_where({-inc => 1}, $0));
    },
    'append|a=s@' => \@append_files,
    'file|F=s' => \$changelog_file,
    'force|f' => \$force,
    'verbose|v' => \$verbose,
    'since=s' => sub { $since_date = set_date(@_) },
    'until=s' => sub { $until_date = set_date(@_) },
    'strip-cherry-pick' => \$strip_cherry_pick,
    'amend=s' => \$amend_file,
    'append-dot' => \$append_dot
    ) or exit(1);

if (! -d '.git') {
    exit 0;
}

read_amend_file($amend_file) if $amend_file;
    
$Text::Wrap::columns = 72;

create_changelog();


sub toplevel_entry {
    my ($hash, $date) = split / /,
          `git log --max-count=1 --pretty=format:'%H %ad' --date=short HEAD`;

    my @modlines;
    if (open(my $fd, '-|', 'git diff-index --name-status HEAD 2>/dev/null')) {
	chomp(@modlines = map {chomp; [split /\s+/, $_, 2]} <$fd>);
	close $fd;
    }

    if (@modlines) {
	$date = strftime '%Y-%m-%d', localtime;
    }

    my @header;

    push @header, "$date  Automatically generated  <bug-mailutils\@gnu.org>";
    push @header, '';
    push @header, "\tHEAD $hash.";
    push @header, '';

    my %status = (
	A => 'New file',
	C => 'Copied file',
	D => 'Removed file',
	M => 'Changed',
	R => 'Renamed',
	T => 'Type change',
	U => 'Unmerged',
	X => 'Unknown'
    );

    if (@modlines) {
	push @header, "\tUncommitted changes:";
	push @header, '';
	
	push @header, map {
	    "\t* $_->[1]: " . ($status{$_->[0]} || 'Unknown') . ";"
	} @modlines;
	push @header, '';
    }
    return @header;
}

sub headcmp {
    my $file = shift;
    if (open(my $fd, '<', $changelog_file)) {
	while (<$fd>) {
	    my $line = shift;
	    last unless defined($line);
	    chomp;
	    return 0 unless $line eq $_;
	}
	return 1 unless @_;
    }
    return 0;
}

sub read_amend_file {
    my ($file) = @_;
    open(my $fd, '<', $file)
	or die "can't open $file for reading: $!";
    use constant {
	STATE_INIT => 1,
	STATE_HASH => 2,
    };
    my $state = STATE_INIT;
    my $silent;
    my $hash;
    my $code;
    my $locus;
    while (<$fd>) {
	chomp;
	s/^\s+//;
	next if /^#/;
	if ($state == STATE_INIT) {
	    if (/^([0-9a-fA-F]{40})$/) {
		$hash = lc $1;
		if (exists($amendment{$hash})) {
		    warn "$file:$.: duplicate SHA1 hash";
		    warn $amendment{$hash}{locus} . ": previously defined here";
		}
		$code = '';
		$locus = "$file:$.";
		$state = STATE_HASH;
		$silent = 0;
	    } elsif (/^$/) {
		next;
	    } else {
		warn "$file:$.: expected SHA1, but found $_"
		    unless $silent;
		$silent = 1;
            }
	} elsif ($state == STATE_HASH) {
	    if (/^$/) {
		$amendment{$hash}{code} = $code;
		$amendment{$hash}{locus} = $locus;
		$state = STATE_INIT;
	    } else {
		$code .= "$_\n";
	    }
	}
    }
    if ($state == STATE_HASH) {
	$amendment{$hash}{code} .= $code;
	$amendment{$hash}{locus} = $locus;
    }
}	

sub tokenize_gitlog {
    my ($q) = @_;
    my @cmd = qw(git log --log-size --no-merges
                 --pretty=format:%H:%ct:%an:%ae%n%s%n%b);

    push @cmd, "--since=$since_date" if defined $since_date;
    push @cmd, "--until=$until_date" if defined $until_date;
    print STDERR "starting @cmd\n" if $verbose > 1;
    
    open(my $fd, '-|', @cmd)
	or die "failed to run git log: $!";
    while (<$fd>) {
	chomp;
	next if /^$/;
	my %ent = ();
	unless (/^log size (\d+)/) {
	    warn "unexpected input: '$_'";
	    next;
	}
	my $size = $1;
	my $log;
	read($fd, $log, $size) == $size or die "unexpected EOF";

	my ($head, $text) = split /\n/, $log, 2;
	($ent{hash},$ent{date},$ent{author},$ent{email}) = split /:/, $head;
	
	if (defined($amendment{$ent{hash}})) {
	    my $code = $amendment{$ent{hash}}{code};
	    print STDERR "amending $ent{hash}\n" if $verbose > 1;
	    print STDERR "code: $code\n" if $verbose > 1;
	    my $s = new Safe;
	    $_ = $text;
	    if (defined(my $r = $s->reval($code))) {
		$text = $_;
		delete $amendment{$ent{hash}};
	    } else {
		warn "$.:$ent{hash}: failed to eval \"$code\" on \"$_\": \n$@\n";
		warn $amendment{$ent{hash}}{locus} . ": code was defined here";
	    }
	}

	my @body;
	($ent{subject}, @body) = split /\n/, $text;

	if ($append_dot && $ent{subject} !~ /[[:punct:]]$/) {
	    $ent{subject} .= '.';
	}
	
	foreach my $line (@body) {
	    if ($line =~ /^Co-authored-by:(.*)$/) {
		my $author = $1;
		if ($author =~ /\s*(.*?)<.+?>$/) {
		    push @{$ent{coauthor}}, [ $1, $2 ];
		}
	    } elsif ($line =~ /^(?:Signed-off-by
                                 |Copyright-paperwork-exempt
                                 |Tiny-change):\s*$/x) {
		next;
	    } elsif ($strip_cherry_pick
		     && $line =~ /^\s*
                                   (?:Conflicts:
                                    |\(cherry picked from commit [\da-f]+\)$)
                                 /x) {
		next;
	    } elsif ($line =~ /^\*/) {
		push @{$ent{body}}, $line;
	    } elsif ($line =~ /^(?:\s
                                 |(?:\(.+?\)\s*
                                   |\[.+?\]\s*
                                   |<.+?>\s*)+:)/x) {
		push @{$ent{body}}, $line;
	    } elsif (exists($ent{body})) {
		${$ent{body}}[-1] .= "\n" . $line;
	    } else {
		if (!exists($ent{description})
		    || ${$ent{description}}[-1] eq ''
		    || $line eq '') {
		    push @{$ent{description}}, $line;
		} else {
		    ${$ent{description}}[-1] .= "\n" . $line;
		}
	    }
	}
	if (exists($ent{body}) && ${$ent{body}}[-1] ne '') {
	    push @{$ent{body}}, '';
	}
	if (exists($ent{description}) && ${$ent{description}}[-1] ne '') {
	    push @{$ent{description}}, '';
	}
	    
	$q->enqueue(\%ent);

    }
    $q->enqueue(undef);
    close $fd;

    my @unused;
    while (my ($hash, $ref) = each %amendment) {
        my $line = $ref->{locus};
	$line =~ s/^.*://;
	push @unused, [ $line, $ref->{locus}, $hash ];
    }
    foreach my $ent (sort { $a->[0] <=> $b->[0] } @unused) {
	warn "$ent->[1]: unused entry: $ent->[2]\n";
    }
    
    print STDERR "tokenize_gitlog finished\n" if $verbose > 1;
}

sub convert_entry {
    my ($q) = @_;
    while (my $ent = $q->dequeue()) {
	print STDERR "Writing $ent->{hash}\n" if $verbose > 1;
	my $date = strftime('%Y-%m-%d', localtime($ent->{date}));
	print $date, '  ', $ent->{author}, '  <', $ent->{email}, ">\n";
	if (exists($ent->{coauthor})) {
	    foreach my $coauthor (@{$ent->{coauthor}}) {
		print '            ', $coauthor->[0], '  ', $coauthor->[1], "\n";
	    }
	}
	print "\n";

	my $tabs = "\t";
	print wrap($tabs, $tabs, $ent->{subject}), "\n\n";
	if (exists($ent->{description})) {
	    foreach my $para (@{$ent->{description}}) {
		print fill($tabs, $tabs, $para), "\n";
	    }
	}
	if (exists($ent->{body})) {
	    foreach my $para (@{$ent->{body}}) {
		print fill($tabs, $tabs, $para), "\n";
	    }
	}
    }
    print STDERR "convert_entry finished\n" if $verbose > 1;
}

sub create_changelog {
    my @header = toplevel_entry;
    if (!$force && headcmp($changelog_file, @header)) {
	print STDERR "$changelog_file is up to date\n" if $verbose > 1;
	return;
    }
    open(my $fd, '>', $changelog_file)
	or die "can't open $changelog_file for writing: $!";
    
    print "  GEN $changelog_file\n" if $verbose;
    print STDERR "updating $changelog_file\n" if $verbose > 1;
    $fd = select($fd);
    # Print header
    for (@header) {
	print "$_\n";
    }

    # Print converted entries
    my $q = Thread::Queue->new();
    my $tok_thr = threads->create(\&tokenize_gitlog, $q);
    my $cvt_thr = threads->create(\&convert_entry, $q);
    $tok_thr->join();
    $cvt_thr->join();

    # Print additional files
    foreach my $file (@append_files) {
	if (open(my $in, '<', $file)) {
	    while (<$in>) {
		chomp;
		last if /^Local Variables:/;
		next if /^\f$/;
		print "$_\n";
	    }
	    close $in;
	} else {
	    warn "can't open $file: $!";
	}
    }

    # Print trailer
    print "\f\nLocal Variables:\n";
    print <<'EOT';
mode: change-log
version-control: never
buffer-read-only: t
End:
EOT
;
    $fd = select($fd);
    close $fd;
}