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Posts Tagged ‘magic the gathering’

Catalyst is easy – something useful

Posted by brunorc on July 30, 2009

Recently I haven’t had much time for writing, because I found a new toy. Somewhat demanding and time consuming toy. But even this toy couldn’t have completely attract all my attention, so some small part of it was still left in the dark corner of my consciousness labelled “Perl”. Soon I discovered that using Perl – and, of course, Catalyst – I can have even more fun playing with my new toy.

Now a short digression: the toy itself is not very new, only I was successfully introduced to it lately. It is the collectible card game, Magic: The Gathering. You may like it, you may hate it, or you may just have no clue about it – it doesn’t matter, as I still want to keep the profile of this blog: Perl, Catalyst, Moose and crap. Well, you can count Magic into the “crap” part if it makes you feel better.

Making long thing short, all I need is a small application, that would serve as a “life counter”. The game is based on the idea of the duel of two wizards. One must die, and that happens when his life counter reaches 0. When the game starts, both counters have the value of 20. As far as I know there is no upper limitation, so in the course of the game wizards can gain even more life. Now you may see why the game is so popular amongst programmers: they are often accused of having no life, and here they start with 20 and can gain even more!

Although there is the possibility of doing Magic in the multiplayer mode, we’re going to start with simple duel of two wizards. Let’s summarize the requirements:

  • two players – we will probably like to know her names
  • every player has a counter, that starts with 20 (with no upper limit); the game ends when one counter reaches 0
  • during the game we want to change the state of both counters, regardless of player’s turn; that’s because there’s a lot of possibilities in Magic, for instance a player can be dealt the damage caused by his own spell that has been redirected

I’m going to keep things simple, so there is no state, no authorization, nothing fancy. Everything will be put in the Root controller and there will be one model to keep the state of the game. I start with creating the application: MagiCount

Notice the advise, added recently:

Change to application directory and Run "perl Makefile.PL" to make sure your install is complete

It is probably a good idea to do this. Now I’m going to create my favourite View, and then the brand new Model:

script/ view TTS TTSite
# output skipped
script/ model Game

Now I’m ready to create the code for the Controller:

sub index :Path :Args(0) {
    my ( $self, $c ) = @_;
    $c->detach( $c->model('Game')->game ? 'play' : 'create' );

I want my actions to be controlled solely by the state of the game. So if the game is defined, I will be able to play – otherwise there’s a need to create one.

sub create :Private {
    my ( $self, $c ) = @_;

    my $p1 = $c->req->params->{player1};
    my $p2 = $c->req->params->{player2};
    my $ct = $c->req->params->{counter};

    if ( $p1 and $p2 ) {
        if ( $p1 eq $p2 ) {
            $c->stash->{errmsg} .= 'Names should be different';
        else {
                [ $p1, $p2 ],
                $ct ? [ $ct, $ct ] : undef


    $c->stash->{template} = 'create.tt2';

In lines 4-6 I’m going to catch the params if they are sent from the form. Then I check them against the obvious condition – players names should be different, otherwise they would start to quarrel about the score. If anything is OK, I intialize the game with the optional parameter – initial value of the counter. It is doubled and passed as an array reference. In that case I’m ready to play, so I use the detach method to exit this action and go directly to the action named play.

Apart from detach there’s also forward, which returns after the action the flow was forwarded to is completed.

Anyway, if the request doesn’t contain any parameters, I’m going to show the template with appropriate form.

sub play :Private {
    my ( $self, $c ) = @_;

    if ( $c->req->params->{close} ) {

    my $c1 = $c->req->params->{counter1};
    my $c2 = $c->req->params->{counter2};

    $c->stash->{game} = $c->model('Game')->game;

    if ( $c1 or $c2 ) {
        $c->stash->{game}->update( [ $c1, $c2 ] );

    $c->stash->{template} = 'play.tt2';

Now I start from the end: I close the game if requested, and then immediately go to create a new one. But if that’s not the case, I’m going to fetch the parameters from request, get the game object, and then update its state. Now the game is ready to be shown, so the only missing thing is the template.

sub default :Path {
    my ( $self, $c ) = @_;
    $c->response->body( 'Page not found' );

That is the standard default action. Nothing fancy.

Now to the Model. I decided to build a simple, singleton class. It will have one arrayref for the names, and then arrayref of arrayrefs for the state of the counters. Maybe it is a little bit convoluted, but will be easier to use in the View later.

my $game;

sub init {
    my ( $class, $names, $counters ) = @_;
    $game = {
        finished => 0,
        players  => $names,
        counters => [ $counters || [ 20, 20 ] ],

    return bless $game, ( ref $class );

First I create my singleton, which becomes a hash reference in line 6, and then – in line 12 – is blessed into the full-fledged class. I pass my names and counters as array references. This is the best way if I want to pass multiple arrays to a function; Perl 6 will have support for names, types and sizes of parameters, but in Perl 5 we have to use array references.

sub update {
    my ( $self, $updates ) = @_;

    push @{ $game->{counters} },
        [ map { $game->{counters}->[-1]->[$_] + $updates->[$_] } (0, 1) ];
    $game->{finished} = 1
        if grep { $_ <= 0 } @{ $game->{counters}->[-1] };

This method gets the array reference of modifiers and then applies them to the current state. I treat the $game->{counters} as an array, so I can push into this. Then I fetch the last item from this array (using the -1 index), and update its elements with respective values. Result of this operation is then pushed.

After this I check if both sorcerers are still alive. If one has deceased, I consider the game as finished. Again, I use the negative index to get the most up-to-date values.

sub close {
    undef $game;

sub game {
    return $game;

sub players {
    return $game->{players};

sub counters {
    return $game->{counters};

sub finished {
    return $game->{finished};

Closing the game means putting the singleton in the undefined state. The rest is just a bunch of accessors.

Now comes the View. No style, just pure HTML.

<h3>Create your game</h3>
<div style="color: red">[% errmsg %]</div>
<form action="" method="post">
      <label for="player1">Name of the first player</label>
       <input type="text" name="player1" size="12" /><br />
      <label for="player2">Name of the second player</label>
       <input type="text" name="player2" size="12" /><br />
       <label for="counter">Initial counter state</label>
       <input type="text" name="counter" size="2" /><br />
       <input type="submit" name="go" value="GO!" />

And the same for playing:

<form action="" method="post">
                <th><strong>[% game.players.0 %]</strong></th>
                <th><strong>[% game.players.1 %]</strong></th>
[% FOREACH state IN game.counters %]
                <td>[% state.0 %]</td><td>[% state.1 %]</td>
[% END %]
[% IF game.finished %]
                <td colspan="2">
                    <input type="submit" name="close" value="GAME OVER!" />
[% ELSE %]
                        <label for="counter1">Modify</label>
                        <input name="counter1" size="3" />
                        <label for="counter2">Modify</label>
                        <input name="counter2" size="3" />
                <td colspan="2">
                    <input type="submit" name="go" value="GO!" />
[% END %]

That’s all. Take out your decks!

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