poker hand classification

use v6;

enum Suit <spades hearts diamonds clubs>;
enum Rank (2, 3, 4, 5, 6, 7, 8, 9, 10,
           'jack', 'queen', 'king', 'ace');

class Card {
    has Suit $.suit;
    has Rank $.rank;

    method Str {
        $.rank.name ~ ' of ' ~ $.suit.name;
    }
}

subset PokerHand of List where { .elems == 5 && all(|$_) ~~ Card }

sub n-of-a-kind($n, @cards) {
    for @cards>>.rank.uniq -> $rank {
        return True if $n == grep $rank, @cards>>.rank;
    }
    return False;
}

subset Quad         of PokerHand where { n-of-a-kind(4, $_) }
subset ThreeOfAKind of PokerHand where { n-of-a-kind(3, $_) }
subset OnePair      of PokerHand where { n-of-a-kind(2, $_) }

subset FullHouse of PokerHand where OnePair & ThreeOfAKind;

subset Flush of PokerHand where -> @cards { [==] @cards>>.suit }

subset Straight of PokerHand where sub (@cards) {
    my @sorted-cards = @cards.sort({ .rank });
    my ($head, @tail) = @sorted-cards;
    for @tail -> $card {
        return False if $card.rank != $head.rank + 1;
        $head = $card;
    }
    return True;
}

subset StraightFlush of Flush where Straight;

subset TwoPair of PokerHand where sub (@cards) {
    my $pairs = 0;
    for @cards>>.rank.uniq -> $rank {
        ++$pairs if 2 == grep $rank, @cards>>.rank;
    }
    return $pairs == 2;
}

sub classify(PokerHand $_) {
    when StraightFlush { 'straight flush',  8 }
    when Quad          { 'four of a kind',  7 }
    when FullHouse     { 'full house',      6 }
    when Flush         { 'flush',           5 }
    when Straight      { 'straight',        4 }
    when ThreeOfAKind  { 'three of a kind', 3 }
    when TwoPair       { 'two pair',        2 }
    when OnePair       { 'one pair',        1 }
    when *             { 'high cards',      0 }
}

my @deck = map -> $suit, $rank { Card.new(:$suit, :$rank) },
                  (Suit.pick(*) X Rank.pick(*));

@deck .= pick(*);

my @hand1;
@hand1.push(@deck.shift()) for ^5;
my @hand2;
@hand2.push(@deck.shift()) for ^5;

say 'Hand 1: ', map { "\n  $_" }, @hand1>>.Str;
say 'Hand 2: ', map { "\n  $_" }, @hand2>>.Str;

my ($hand1-description, $hand1-value) = classify(@hand1);
my ($hand2-description, $hand2-value) = classify(@hand2);

say sprintf q[The first hand is a '%s' and the second one a '%s', so %s.],
    $hand1-description, $hand2-description,
    $hand1-value > $hand2-value
        ?? 'the first hand wins'
        !! $hand2-value > $hand1-value
            ?? 'the second hand wins'
            !! "the hands are of equal value"; # XXX: probably wrong