#!/usr/bin/env perl

## commit-check --- Simple git commit style checker
# Copyright (C) 2014  Tom Willemse <tom@ryuslash.org>

# commit-check is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# commit-check is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with commit-ccheck. If not, see <http://www.gnu.org/licenses/>.

=head1 Commit check

This is a simple commit style checker. It is made to be used as a git
C<commit-msg> hook. It expects the name of the file to check as the
first command-line argument. The style that's checked is based on
tpope's L<A Note About Git Commit
Messages|http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html>.

=head2 Command-line options

There are 2 command line options available for use with this program:

=over

=item -0

Don't return a non-zero status when errors have been found. For use as
a git C<commit-msg> hook it is important that it does exit with a
non-zero status. But if you are using it for other tools, such as for
a flycheck checker, exiting with a non-zero status might confuse the
tools calling it.

=item -h

Show a little help text that describes the command line options and
usage.

=back

When no arguments are passed (not even the file name) the help text is
also shown and the exit status is non-0 (no matter if C<-0> has been
given).

=head2 Errors

Currently there are 4 style errors that are checked for.

=over

=item 1

The first character of the first line of the commit message should be
capitalized.

=item 2

The first line of the commit message should be no longer than 50
characters.

=item 3

The second line of the commit message should be empty.

=item 4

No line should be longer than 72 characters.

=back

All comments are skipped and so is all whitespace at the beginning of
the file.

If any of the error conditions are encountered, and the C<-0> option
has not been given, the program will exit with a non-C<0> status. This
has the effect of stopping git from committing the message when this
program is used as a C<commit-msg> hook. Each error condition
encountered also prints a message to the standard error stream.

=cut

use strict;
use warnings;
use Getopt::Std;

my $lineno = 0;
my $status = 0;
my %arguments = ();

sub err {
    my ($msg) = @_;

    print STDERR "Error on line $lineno (actual line $.): ". $msg ."\n";
    $status = 1;
}

sub usage {
    my ($status) = @_;
    print "Usage: commit-check [-0|-h] <file>\n"
        . "\n"
        . "Accepted arguments:\n"
        . "  -0   Always return 0 exit-status, regardless of errors found.\n"
        . "  -h   Show this help text.\n";
    exit $status;
}

getopts("0h", \%arguments);

usage 0 if $arguments{h};
usage 1 if !$ARGV[0];

open(my $commitfile, "<", $ARGV[0]) or die "Couldn't open $ARGV[0]";

while (<$commitfile>) {
    next if /^#/;                 # Discard comments
    next if $lineno == 0 && /^$/; # Discard leading empty lines
    $lineno++;                    # Start at 1, so increment first

    if ($lineno == 1) {
        err "Not capitalized" if /^[^[:upper:]]/;
        err "Longer than 50 characters" if /^.{51,}/;
        next;
    }

    err "Should be empty" if $lineno == 2 && /.+/;
    err "Longer than 72 characters" if /^.{73,}/;
}

close $commitfile;
exit $status if !$arguments{0};
exit 0;