#!/usr/bin/perl

use Perl6::Slurp;
use Data::Dumper;

my $g = slurp $ARGV[0];

$g =~ s{\n\=begin.*?\n(.|\n)*?=end.*?\n}{}g;
$g =~ s[#.*?$][]gm;
$g =~ s[^((rule|token)\s+(\S+))][$1\n]mg;
$g =~ s[\<[.?!]?([^<>]*?(\<.*?\>)?)\>][\nitem $1\n]g;

my @a = split /\n/, $g;

map { $_ =~ s/item before \<(.*)\>/item $1/; } @a;
map { $_ =~ s/item (\S+): .*/item $1/; } @a;
(my $grammar) = grep(/^grammar/, @a);
$grammar =~ s/grammar\s+(\w+).*/$1/;
@a = grep(/^(token|rule|item)/, @a);
@a = grep(!/item \[/, @a);
@a = grep(!/^item before/, @a);
@a = grep(!/^item (?!\w+$)/, @a);

my $curr_token;

print "digraph $grammar {\n";

map { my $line = $_;
    if($line =~ m/^(token|rule) (.*)/) {
        $curr_token = $2;
    }
    elsif($line =~ m/^item (.*)/) {
        print "$curr_token -> $1;\n";
    }
} @a;

print "}\n";