use Script ();

# Data extracted from XML.
my %snippets = (
   onInit   => 'use strict; my $x=2;',
   onAwaken => 'print ++$y;',
);

my $script = Script->new(\%snippets);
$script->onInit();
$script->onAwaken();

##</code><code>##

Global symbol "$y" requires explicit package name in onAwaken.

##</code><code>##

use strict;
use warnings;

package Script;

# Constants.

my @events = qw(
   preRestore
   onRestore
   onAttach
   onInit
   onAwaken
   onChange
); # Ordered.

my %events = map { $events[$_] => $_ } 0..$#events;


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

   my @event_line_nums;

   my $code = "sub {\n";
   $code .= "   my \$event_num = shift;\n";
   $code .= "   goto __$events[$_] if \$event_num == $_;\n"
      foreach 0 .. $#events;

   foreach my $event (@events) {
      push @event_line_nums, (() = $code =~ /\n/g) + 1;
      
      if (defined $snippets->{$event}) {
         $code .= "__$event: 1;\n$snippets->{$event}; return;\n";
      } else {
         $code .= "__$event: return;\n";
      }
   }

   $code .= "\n}\n";

   my $sub = eval $code;
   if ($@) {
      my ($error_msg, $line_num) =
         $@ =~ /^(.*) at \(eval \d+\) line (\d+)/s;

      my $error_event;
      foreach my $event_num (0..$#events) {
         last if $line_num < $event_line_nums[$event_num];
         $error_event = $event_num;
      }

      die("$error_msg in $events[$error_event].\n");
   }

   return bless($sub, $class);
}

sub _dispatch {
   my $sub       = shift;
   my $event_num = shift;

   $rv = eval { $sub->($event_num, @_) };
   if ($@) {
      my ($error_msg) =
         $@ =~ /^(.*) at \(eval \d+\) line /s;

      die("$error_msg in $events[$event_num].\n");
   }

   return $rv;
}

eval "sub $_ { shift->_dispatch($events{$_}, \@_); }"
   foreach @events;

1;