#!perl
use 5.010;
use strict;
use warnings;
use lib 'Porting';
use Maintainers qw/%Modules/;
use Module::CoreList;
use Getopt::Long;
use Algorithm::Diff;

my %sections = (
  new     => 'New Modules and Pragmata',
  updated => 'Updated Modules and Pragma',
  removed => 'Removed Modules and Pragmata',
);

my $deprecated;

#--------------------------------------------------------------------------#

sub added {
  my ($mod, $old_v, $new_v) = @_;
  say "=item *\n";
  say "C<$mod> $new_v has been added to the Perl core.\n";
}

sub updated {
  my ($mod, $old_v, $new_v) = @_;
  say "=item *\n";
  say "C<$mod> has been upgraded from version $old_v to $new_v.\n";
  if ( $deprecated->{$mod} ) {
    say "NOTE: C<$mod> is deprecated and may be removed from a future version of Perl.\n";
  }
}

sub removed {
  my ($mod, $old_v, $new_v) = @_;
  say "=item *\n";
  say "C<$mod> has been removed from the Perl core.  Prior version was $old_v.\n";
}

sub generate_section {
  my ($title, $item_sub, @mods ) = @_;
  return unless @mods;

  say "=head2 $title\n";
  say "=over 4\n";

  for my $tuple ( sort { lc($a->[0]) cmp lc($b->[0]) } @mods ) {
    my ($mod,$old_v,$new_v) = @$tuple;
    $old_v //= q('undef');
    $new_v //= q('undef');
    $item_sub->($mod, $old_v, $new_v);
  }

  say "=back\n";
}

#--------------------------------------------------------------------------#

sub run {
  my %opt = (mode => 'generate');

  GetOptions(\%opt,
    'mode|m:s', # 'generate', 'check'
  );

  # by default, compare latest two version in CoreList;
  my @versions = sort keys %Module::CoreList::version;
  my ($old, $new) = (shift @ARGV, shift @ARGV);
  $old ||= $versions[-2];
  $new ||= $versions[-1];

  if ( $opt{mode} eq 'generate' ) {
    do_generate($old => $new);
  }
  elsif ( $opt{mode} eq 'check' ) {
    do_check(\*ARGV, $old => $new);
  }
  else {
    die "Unrecognized mode '$opt{mode}'\n";
  }

  exit 0;
}

sub corelist_delta {
  my ($old, $new) = @_;
  my $corelist = \%Module::CoreList::version;

  $deprecated = $Module::CoreList::deprecated{$new};

  my (@new,@deprecated,@removed,@pragmas,@modules);

  # %Modules defines what is currently in core
  for my $k ( keys %Modules ) {
    next unless exists $corelist->{$new}{$k};
    my $old_ver = $corelist->{$old}{$k};
    my $new_ver = $corelist->{$new}{$k};
    # in core but not in last corelist
    if ( ! exists $corelist->{$old}{$k} ) {
      push @new, [$k, undef, $new_ver];
    }
    # otherwise just pragmas or modules
    else {
      my $old_ver = $corelist->{$old}{$k};
      my $new_ver = $corelist->{$new}{$k};
      next unless defined $old_ver && defined $new_ver && $old_ver ne $new_ver;
      my $tuple = [ $k, $old_ver, $new_ver ];
      if ( $k eq lc $k ) {
        push @pragmas, $tuple;
      }
      else {
        push @modules, $tuple;
      }
    }
  }

  # in old corelist, but not this one => removed
  # N.B. This is exhaustive -- not just what's in %Modules, so modules removed from
  # distributions will show up here, too.  Some person will have to review to see what's
  # important. That's the best we can do without a historical Maintainers.pl
  for my $k ( keys %{ $corelist->{$old} } ) {
    if ( ! exists $corelist->{$new}{$k} ) {
      push @removed, [$k, $corelist->{$old}{$k}, undef];
    }
  }

  return (\@new, \@removed, \@pragmas, \@modules);
}

sub do_generate {
  my ($old, $new) = @_;
  my ($added, $removed, $pragmas, $modules) = corelist_delta($old => $new);

  generate_section($sections{new}, \&added, @{ $added });
  generate_section($sections{updated}, \&updated, @{ $pragmas }, @{ $modules });
  generate_section($sections{removed}, \&removed, @{ $removed });
}

sub do_check {
  my ($in, $old, $new) = @_;

  my $delta = DeltaParser->new($in);
  my ($added, $removed, $pragmas, $modules) = corelist_delta($old => $new);

  for my $ck (['new',     $delta->new_modules, $added],
              ['removed', $delta->removed_modules, $removed],
              ['updated', $delta->updated_modules, [@{ $modules }, @{ $pragmas }]]) {
    my @delta = @{ $ck->[1] };
    my @corelist = sort { lc $a->[0] cmp lc $b->[0] } @{ $ck->[2] };

    printf $ck->[0] . ":\n";

    my $diff = Algorithm::Diff->new(map {
      [map { join q{ } => grep defined, @{ $_ } } @{ $_ }]
    } \@delta, \@corelist);

    while ($diff->Next) {
      next if $diff->Same;
      my $sep = '';
      if (!$diff->Items(2)) {
        printf "%d,%dd%d\n", $diff->Get(qw( Min1 Max1 Max2 ));
      } elsif(!$diff->Items(1)) {
        printf "%da%d,%d\n", $diff->Get(qw( Max1 Min2 Max2 ));
      } else {
        $sep = "---\n";
        printf "%d,%dc%d,%d\n", $diff->Get(qw( Min1 Max1 Min2 Max2 ));
      }
      print "< $_\n" for $diff->Items(1);
      print $sep;
      print "> $_\n" for $diff->Items(2);
    }

    print "\n";
  }
}

{
  package DeltaParser;
  use Pod::Simple::SimpleTree;

  sub new {
    my ($class, $input) = @_;

    my $self = bless {} => $class;

    my $parsed_pod = Pod::Simple::SimpleTree->new->parse_file($input)->root;
    splice @{ $parsed_pod }, 0, 2; # we don't care about the document structure,
                                   # just the nods within it

    $self->_parse_delta($parsed_pod);

    return $self;
  }

  for my $k (keys %sections) {
    no strict 'refs';
    my $m = "${k}_modules";
    *$m = sub { $_[0]->{$m} };
  }

  sub _parse_delta {
    my ($self, $pod) = @_;

    map {
        my ($t, $s) = @{ $_ };
        $self->${\"_parse_${t}_section"}($s)
    } map {
        my $s = $self->_look_for_section($pod => $sections{$_});
        $s ? [$_, $s] : $s
    } keys %sections;

    for my $s (keys %sections) {
      my $m = "${s}_modules";

      $self->{$m} = [sort {
        lc $a->[0] cmp lc $b->[0]
      } @{ $self->{$m} }];
    }

    return;
  }

  sub _parse_new_section {
    my ($self, $section) = @_;

    $self->{new_modules} = $self->_parse_section($section => sub {
      my ($el) = @_;

      my ($first, $second) = @{ $el }[2, 3];
      my ($ver) = $second =~ /(\d[^\s]+)\s+has\s+been/;

      return [ $first->[2], undef, $ver ];
    });

    return;
  }

  sub _parse_updated_section {
    my ($self, $section) = @_;

    $self->{updated_modules} = $self->_parse_section($section => sub {
      my ($el) = @_;

      my ($first, $second) = @{ $el }[2, 3];
      my $module = $first->[2];
      my ($old, $new) = $second =~
          /from\s+(?:version\s+)?(\d[^\s]+)\s+to\s+(\d[^\s]+?)\.?$/;

      warn "Unable to extract old or new version of $module from perldelta"
        if !defined $old || !defined $new;

      return [ $module, $old, $new ];
    });

    return;
  }

  sub _parse_removed_section {
    my ($self, $section) = @_;
    $self->{removed_modules} = $self->_parse_section($section => sub {
      my ($el) = @_;

      my ($first, $second) = @{ $el }[2, 3];
      my ($old) = $second =~ /was\s+(\d[^\s]+?)\.?$/;

      return [ $first->[2], $old, undef ];
    });

    return;
  }

  sub _parse_section {
    my ($self, $section, $parser) = @_;

    my $items = $self->_look_down($section => sub {
      my ($el) = @_;
      return unless ref $el && $el->[0] =~ /^item-/
          && @{ $el } > 2 && ref $el->[2];
      return unless $el->[2]->[0] eq 'C';

      return 1;
    });

    return [map { $parser->($_) } @{ $items }];
  }

  sub _look_down {
    my ($self, $pod, $predicate) = @_;
    my @pod = @{ $pod };

    my @l;
    while (my $el = shift @pod) {
      push @l, $el if $predicate->($el);
      if (ref $el) {
        my @el = @{ $el };
        splice @el, 0, 2;
        unshift @pod, @el if @el;
      }
    }

    return @l ? \@l : undef;
  }

  sub _look_for_section {
    my ($self, $pod, $section) = @_;

    my $level;
    $self->_look_for_range($pod,
      sub {
        my ($el) = @_;
        my $f = $el->[0] =~ /^head(\d)$/ && $el->[2] eq $section;
        $level = $1 if $f && !$level;
        return $f;
      },
      sub {
        my ($el) = @_;
        $el->[0] =~ /^head(\d)$/ && $1 <= $level;
      },
    );
  }

  sub _look_for_range {
    my ($self, $pod, $start_predicate, $stop_predicate) = @_;

    my @l;
    for my $el (@{ $pod }) {
      if (@l) {
        return \@l if $stop_predicate->($el);
      }
      else {
        next unless $start_predicate->($el);
      }
      push @l, $el;
    }

    return;
  }
}

run;