#!/usr/bin/perl

use 5.028;
use strict;
use warnings;

use Cwd;
use File::Spec::Functions "catfile";
use Git::Wrapper;
use Sys::Hostname;

my $git = Git::Wrapper->new(getcwd);

($git->rev_parse({ abbrev_ref => 1 }, "HEAD"))[0] eq "athena/unstable"
  or $git->checkout("athena/unstable");

my ($to_merge) = $git->merge_base(hostname, "origin/master");

chomp(my $prev_version = `dpkg-parsechangelog -SVersion`);
chomp(my $prev_distn   = `dpkg-parsechangelog -SDistribution`);

my ($prev_date, $prev_rev) = ($prev_version =~ /git([0-9]+).([0-9]+)/);
my ($new_date) = $git->show("-s", { format => "%ci" }, $to_merge);
$new_date =~ /\A([0-9]{4})-([0-9]{2})-([0-9]{2})/
  or die "couldn't parse new commit committer date";
$new_date = $1 . $2 . $3;
my $new_rev = $prev_date eq $new_date ? $prev_rev + 1 : 1;

$git->merge({
        message => "Merge upstream Git snapshot into athena/unstable"
    },
    $to_merge
);

my $major_version;
open my $fh, "<", catfile $git->dir, "configure.ac";
for (<$fh>) {
    $major_version = $1, last
      if /AC_INIT\(\[GNU Emacs\], \[([0-9]+)\.0\.[56]0\],/
}
$major_version or die "couldn't extract devel major version number";

# We use .1 not .0.50 because that's what's conventional
# with Debian "~gitYYYYMMDD.N" git snapshot version numbers.
system "dch", "-v${major_version}.1~git${new_date}.${new_rev}",
  $prev_distn eq "UNRELEASED" ? "" : "Package git snapshot.";
$git->add("debian/changelog");
$git->commit({ message => "changelog" });