#!perl
use strict;
use warnings;
use Getopt::Long qw/GetOptions/;
use Term::ANSIColor qw/color/;
use constant GITCMD => 'git';
sub usage {
  print <<HERE;
Usage: $0 [options] [<start-commit> [<end-commit>]]
Scans the commit logs for commits that are potentially, illegitimately
touching modules that are primarily maintained outside of the perl core.
Also checks for commits that span multiple distributions in cpan/ or dist/.
Makes sure that updated CPAN distributions also update Porting/Maintainers.pl,
but otherwise ignores changes to that file (and MANIFEST).
Skip the <start-commit> to go back indefinitely. <end-commit> defaults to
HEAD.
 -h/--help shows this help
 -v/--verbose shows the output of "git show --stat <commit>" for each commit
 -c/--color uses colored output
HERE
  exit(1);
}
our $Verbose = 0;
our $Color   = 0;
GetOptions(
  'h|help'         => \&usage,
  'v|verbose'      => \$Verbose,
  'c|color|colour' => \$Color,
);
my $start_commit = shift;
my $end_commit   = shift;
$end_commit = 'HEAD' if not defined $end_commit;
my $commit_range_cmd = defined($start_commit) ? " $start_commit..$end_commit" : "";
# format: hash\0author\0committer\0short_msg
our $LogCmd = GITCMD() . q{ log --no-color -M -C --name-only '--pretty=format:%h%x00%an%x00%cn%x00%s'} . $commit_range_cmd;
our @ColumnSpec = qw(hash author committer commit_msg);
open my $fh, '-|', $LogCmd
  or die "Can't run '$LogCmd' to get the commit log: $!";
my ($safe_commits, $unsafe_commits) = parse_log($fh);
if (@$unsafe_commits) {
  my $header = "Potentially unsafe commits:";
  print color("red") if $Color;
  print $header, "\n";
  print("=" x length($header), "\n\n") if $Verbose;
  print color("reset") if $Color;
  print_commit_info($_) foreach reverse @$unsafe_commits;
  print "\n";
}
if (@$safe_commits) {
  my $header = "Presumably safe commits:";
  print color("green") if $Color;
  print $header, "\n";
  print("=" x length($header), "\n") if $Verbose;
  print color("reset") if $Color;
  print_commit_info($_) foreach reverse @$safe_commits;
  print "\n";
}
exit(0);
# single-line info about the commit at hand
sub print_commit_info {
  my $commit = shift;
  my $author_info = "by $commit->{author}"
                    . ($commit->{author} eq $commit->{committer}
                       ? ''
                       : " committed by $commit->{committer}");
  if ($Verbose) {
    print color("yellow") if $Color;
    my $header = "$commit->{hash} $author_info: $commit->{msg}";
    print "$header\n", ("-" x length($header)), "\n";
    print color("reset") if $Color;
    my $cmd = GITCMD() . ' show --stat ' . ($Color?'--color ':'')
              . $commit->{hash};
    print `$cmd`; # make sure git knows this isn't a terminal
    print "\n";
  }
  else {
    print color("yellow") if $Color;
    print "  $commit->{hash} $author_info: $commit->{msg}\n";
    print color("reset") if $Color;
  }
}
# check whether the commit at hand is safe, unsafe or uninteresting
sub check_commit {
  my $commit = shift;
  my $safe   = shift;
  my $unsafe = shift;
  # Note to self: Adding any more greps and such will make this
  # look even more silly. Just use a single foreach, smart guy!
  my $touches_maintainers_pl = 0;
  my @files = grep {
                $touches_maintainers_pl = 1
                  if $_ eq 'Porting/Maintainers.pl';
                $_ ne 'MANIFEST' and $_ ne 'Porting/Maintainers.pl'
              }
              @{$commit->{files}};
  my @touching_cpan = grep {/^cpan\//} @files;
  return if not @touching_cpan;
  # check for unsafe commits to cpan/
  my %touched_cpan_dirs;
  $touched_cpan_dirs{$_}++ for grep {defined $_}
                               map {s/^cpan\/([^\/]*).*$/$1/; $_}
                               @touching_cpan;
  my $touches_multiple_cpan_dists = (keys(%touched_cpan_dirs) > 1);
  my $touches_others              = @files - @touching_cpan;
  if (@touching_cpan) {
    if ($touches_others) {
      $commit->{msg} = 'Touched files under cpan/ and other locations';
      push @$unsafe, $commit;
    }
    elsif ($touches_multiple_cpan_dists) {
      $commit->{msg} = 'Touched multiple directories under cpan/';
      push @$unsafe, $commit;
    }
    elsif (not $touches_maintainers_pl) {
      $commit->{msg} = 'Touched files under cpan/, but does not update '
                       . 'Porting/Maintainers.pl';
      push @$unsafe, $commit;
    }
    elsif ($commit->{commit_msg} =~ /(?:up(?:grad|dat)|import)(?:ed?|ing)/i) {
      $commit->{msg} = 'Touched files under cpan/ with '
                       . '"upgrading"-like commit message';
      push @$safe, $commit;
    }
    else {
      $commit->{msg} = 'Touched files under cpan/ without '
                       . '"upgrading"-like commit message';
      push @$unsafe, $commit;
    }
  }
  # check for unsafe commits to dist/
  my @touching_dist = grep {/^dist\//} @files;
  my %touched_dist_dirs;
  $touched_dist_dirs{$_}++ for grep {defined $_}
                               map {s/^dist\/([^\/]*).*$/$1/; $_}
                               @touching_dist;
  $touches_others = @files - @touching_dist;
  my $touches_multiple_dists = (keys(%touched_dist_dirs) > 1);
  if (@touching_dist) {
    if ($touches_others) {
      $commit->{msg} = 'Touched files under dist/ and other locations';
      push @$unsafe, $commit;
    }
    elsif ($touches_multiple_dists) {
      $commit->{msg} = 'Touched multiple directories under cpan/';
      push @$unsafe, $commit;
    }
  }
}
# given file handle, parse the git log output and put the resulting commit
# structure into safe/unsafe compartments
sub parse_log {
  my $fh = shift;
  my @safe_commits;
  my @unsafe_commits;
  my $commit;
  while (defined(my $line = <$fh>)) {
    chomp $line;
    if (not $commit) {
      next if $line =~ /^\s*$/;
      my @cols = split /\0/, $line;
      @cols == @ColumnSpec && !grep {!defined($_)} @cols
        or die "Malformed commit header line: '$line'";
      $commit = {
        files => [],
        map {$ColumnSpec[$_] => $cols[$_]} (0..$#cols)
      };
      next;
    }
    elsif ($line =~ /^\s*$/) { # within commit, blank line
      check_commit($commit, \@safe_commits, \@unsafe_commits);
      $commit = undef;
    }
    else { # within commit, non-blank (file) line
      push @{$commit->{files}}, $line;
    }
  }
  return(\@safe_commits, \@unsafe_commits);
}