/ 
Game-Durak-0.01
/ Game::Durak::Deck

NAME

Game::Durak::Deck - the seeded deal, and the talon with the trump underneath it

VERSION

Version 0.01

SYNOPSIS

use Game::Durak::Deck qw(order_for deal_for first_attacker);

my $deal = deal_for($seed, 1);

$deal->{hands}{1};      # six ids, sorted
$deal->{hands}{2};      # six ids, sorted
$deal->{talon};         # twenty-four ids in draw order, the turn-up LAST
$deal->{trump_card};    # the turned up card, face up, still in the talon
$deal->{trump};         # its suit
$deal->{first};         # the seat holding the lowest trump

DESCRIPTION

One shuffle per deal, from the seed and the deal number, with no call to rand anywhere. A deal is a pure function of its seed, so a finished game replays on any machine and can be checked by anybody once the seed is published.

The turn-up is part of the talon

The next card is placed face up in the centre of the table; its suit
determines trumps. The remaining undealt cards are placed in a stack face
down on top of the trump card, but crosswise so that the rank and value of
the trump remain visible.
    -- https://www.pagat.com/beating/podkidnoy_durak.html

The turn-up remains part of the talon and is drawn as the last card.
    -- https://en.wikipedia.org/wiki/Durak

So talon holds twenty-four ids at two seats: the twenty-three face down cards in draw order, and then the turned up trump. It is not a card held beside the talon, and a deal that returns twenty-three and a trump card alongside leaves the last two bouts of every deal a card short, which is exactly where a durak deal is decided.

Putting it at the end of the order also makes a draw unconditionally "take the next one", with no special case at the bottom of the pile, and it makes a draw derivable from the seed and the number of draws already made. A consumer that keeps hands secret then gets that for free: a payload that never held the card cannot leak it.

The deal number is in the key

A deal is one game here, so the deal number is always 1 today. It is an argument all the same, so that a variant playing several deals to a session cannot deal the same cards every time from one seed. That failure looks like extraordinary luck rather than like a fault.

The shuffle

Fisher-Yates over the thirty-six ids, driven by 32-bit words from SHA-256 of the seed and the key, rejecting any word past the largest multiple of the range so that no position is favoured.

This is the sixteenth copy of that routine in the family, counted on 25 September 2026 with grep -rl 'sub order_for' --include='*.pm' over Semantic with the mutation scratch tree excluded: the five in Game::Blackjack, Game::Dominoes, Game::Gin, Game::Mahjong and Game::Schnapsen, and the ten in the site's own games. They are meant to stay in step, and a shared module is refused for the reason Hearts' deck states: every game's fixtures are pinned to the order its own copy produces, so one shared copy would move every game's vectors to fix none of them.

This copy differs from the others in the size of the pack and in the stream key, and in nothing else.

Who opens

In the first hand of a session, the holder of the lowest trump plays
first. If anyone has the trump 6 they show it to prove they are entitled
to begin. If no one has the trump 6, then the holder of the trump 7 will
start; if no one has that, the trump 8 and so on. The first play does not
have to include the lowest trump.
    -- https://www.pagat.com/beating/podkidnoy_durak.html

first_attacker is the minimum of one list rather than a walk down the ranks, because the walk reads as nine special cases and is nine chances to write the comparison backwards.

The card is never shown. The source has the opener prove the right by showing the six; here the deal has already proved it, so only the seat number is published. The inference that remains, that the opener holds a trump at least as low as your own lowest, is the game's own and is the same across a table.

Neither seat holding a trump is a legal deal. Twelve cards are dealt and the turn-up is a thirteenth, so the eight remaining trumps can all be in the talon; it happened in 87 of 5000 seeded deals, one in 57. The opener is then seat 1, which is this distribution's rule and not the source's, because the source does not say.

FUNCTIONS

Nothing is exported by default.

order_for

my $order = order_for($seed, $deal);

The thirty-six ids in shuffled order. Dies unless the seed is exactly 32 bytes and the deal number is a positive integer.

deal_for

my $deal = deal_for($seed, $deal, $seats);

Six cards each dealt singly, seat 1 first, then the turn-up, then the talon. $seats defaults to two and dies at anything else: three and more seats need a throw-in by a player who is not on turn, which is a different game to arbitrate and a plan of its own.

The sub is deal_for rather than deal so that it does not take an argument with its own name.

first_attacker

my $seat = first_attacker($deal->{hands}, $deal->{trump});

The seat holding the lowest trump, or the lowest numbered seat if no hand holds one. Dies unless the trump is a suit, because a mistyped suit would otherwise answer seat 1 and look like the fallback.

HAND_SIZE, SEATS

Six and two, as constants.

SEE ALSO

Game::Durak, Game::Durak::Card.

AUTHOR

LNATION, <email@lnation.org>

LICENSE AND COPYRIGHT

This software is Copyright (c) 2026 by LNATION.

This is free software, licensed under the Artistic License 2.0.