#!/usr/bin/perl

=head1 NAME

gitlog2changelog - tiny tool to convert Git commit logs to GNU ChangeLog

=head1 SYNOPSIS

git log | gitlog2changelog > ChangeLog

git log --no-merges --numstat | gitlog2changelog > ChangeLog

(Use --no-merges to ignore merge commits.
 Use --numstat to show changed files.)

=head1 SEE ALSO

GNU Coding Standards:
    <http://www.gnu.org/prep/standards/html_node/index.html>
    <http://www.gnu.org/prep/standards/html_node/Change-Logs.html>

=head1 COPYRIGHT

Copyright (c) 2013 Tatsuya Kinoshita

Redistribution and use in source and binary forms, with or without
modification, are permitted without restriction, with NO WARRANTY.
You may regard this as a work that is placed in the public domain.

=cut

use strict;
use warnings;

my $author = ""; my $date = ""; my $comment = ""; my @files = ();
my $pre_header = "";

sub print_entry {
    my $header = "$date  $author";
    $header =~ s/ </  </;
    if ($header ne $pre_header) {
	print "$header\n\n";
	$pre_header = $header;
    }
    print "\t* ";

    my $files_line_len = 10;
    my $files_lines = "";
    foreach my $file (@files) {
	my $len = length($file);
	if ($files_line_len > 10 && ($files_line_len + $len > 78)) {
	    $files_lines =~ s/, $/:\n\t* /;
	    $files_line_len = 10;
	}
	$files_lines .= "$file, ";
	$files_line_len += $len + 2;
    }

    if ($files_lines) {
	my $short_comment = "";
	if ($comment =~ /^([^\n]+)/) {
	    $short_comment = $1;
	}
	if ($short_comment =~ /:[ \t]|[:,\)][ \t]*$/ ||
	    $files_line_len + length($short_comment) > 78) {
	    $files_lines =~ s/, $/:\n\t/;
	} else {
	    $files_lines =~ s/, $/: /;
	}
	print "$files_lines";
    }

    $comment =~ s/\n([ \t]*\n)+/\n/g;
    $comment =~ s/\n+$//;
    $comment =~ s/\n/\n\t/g;
    $comment =~ s/^\* //;
    print "$comment\n\n";

    $author = ""; $date = ""; $comment = ""; @files = ();
}

while (<>) {
    if (/^Author:[ \t]+([^\n]+)/) {
	$author = $1;
    } elsif (/^Date:[ \t]+(Sun|Mon|Tue|Wed|Thu|Fri|Sat) +(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec) +(\d+) +\d+:\d+:\d+ +(\d+)/) {  # Assume git log --date=default or --date=local
	my $mm = $2;
	my $dd = $3;
	my $yyyy = $4;
	$mm =~ s/Jan/01/; $mm =~ s/Feb/02/; $mm =~ s/Mar/03/; $mm =~ s/Apr/04/;
	$mm =~ s/May/05/; $mm =~ s/Jun/06/; $mm =~ s/Jul/07/; $mm =~ s/Aug/08/;
	$mm =~ s/Sep/09/; $mm =~ s/Oct/10/; $mm =~ s/Nov/11/; $mm =~ s/Dec/12/;
	$dd =~ s/^(\d)$/0$1/;
	$date = "$yyyy-$mm-$dd";
    } elsif (/^Date:[ \t]+(\d+-\d+-\d+)/) {  # Assume git log --date=short or --date=iso
	$date = $1;
    } elsif (/^Date:[ \t]+(.+)$/) {
	$date = $1;
    } elsif (/^    (.*)$/) {
	$comment .= "$1\n";
    } elsif (/^[-0-9]+\t[-0-9]+\t(.*)$/) {  # Assume git log --numstat
	push @files, $1;
    } elsif (/^commit / && $author && $date) {
	&print_entry;
    }
}
if ($author && $date) {
    &print_entry;
}