feat: Get hand rank

Method to get rank of a given hand.

3 files changed, 110 insertions, 0 deletions

diff --git a/poker/rank/__init__.py b/poker/rank/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/poker/rank/__init__.py
diff --git a/poker/rank/descriptions.py b/poker/rank/descriptions.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/poker/rank/descriptions.py
diff --git a/poker/rank/hands.py b/poker/rank/hands.py
new file mode 100644
index 0000000..8764ce9
--- /dev/null
+++ b/poker/rank/hands.py
@@ -0,0 +1,110 @@
+from poker.constants import Rank, Value
+from poker.models import Card, Hand
+
+
+def _is_flush(cards: list[Card]) -> bool:
+    """Calculate whether hand is a flush."""
+    return len(set(card.suit for card in cards)) == 1
+
+
+def _is_straight(cards: list[Card]) -> bool:
+    """Calculate whether hand is a straight."""
+    card_values = sorted([card.value for card in cards])
+
+    # If card values are not unique it is not a straight
+    if len(set(card_values)) != len(card_values):
+        return False
+
+    # Check for a ace low straight
+    if card_values == [Value.TWO, Value.THREE, Value.FOUR, Value.FIVE, Value.ACE]:
+        return True
+
+    # If all card differences are 1 it is a straight
+    diffs = [second - first for first, second in zip(card_values[:-1], card_values[1:])]
+    if set(diffs) == {1}:
+        return True
+
+    return False
+
+
+def is_royal_flush(hand: Hand) -> bool:
+    """Calculate whether hand a royal flush."""
+    if not _is_flush(hand.cards):
+        return False
+
+    values = [card.value for card in hand.cards]
+    return all(
+        value in values
+        for value in [Value.ACE, Value.KING, Value.QUEEN, Value.JACK, Value.TEN]
+    )
+
+
+def is_straight_flush(hand: Hand) -> bool:
+    """Calculate whether hand a straight flush."""
+    return _is_straight(hand.cards) and _is_flush(hand.cards)
+
+
+def is_four_of_a_kind(hand: Hand) -> bool:
+    """Calculate whether hand has four of a kind."""
+    return hand.value_counts[0][1] == 4
+
+
+def is_full_house(hand: Hand) -> bool:
+    """Calculate whether hand is a full house."""
+    return hand.value_counts[0][1] == 3 and hand.value_counts[1][1] == 2
+
+
+def is_flush(hand: Hand) -> bool:
+    """Calculate whether hand is a flush."""
+    return _is_flush(hand.cards) and not _is_straight(hand.cards)
+
+
+def is_straight(hand: Hand) -> bool:
+    """Calculate whether hand is a flush."""
+    return _is_straight(hand.cards) and not _is_flush(hand.cards)
+
+
+def is_three_of_a_kind(hand: Hand) -> bool:
+    """Calculate whether hand is a full house."""
+    return (
+        hand.value_counts[0][1] == 3
+        and hand.value_counts[1][1] == 1
+        and hand.value_counts[2][1] == 1
+    )
+
+
+def is_two_pair(hand: Hand) -> bool:
+    """Calculate whether hand is a two pair."""
+    return hand.value_counts[0][1] == 2 and hand.value_counts[1][1] == 2
+
+
+def is_pair(hand: Hand) -> bool:
+    """Calculate whether hand is a pair."""
+    return hand.value_counts[0][1] == 2 and hand.value_counts[1][1] == 1
+
+
+def get_rank(hand: Hand) -> Rank:
+    """Get hand rank.
+
+    TODO: Use a factory pattern to avoid this huge flow control.
+    """
+    if is_royal_flush(hand):
+        return Rank.ROYAL_FLUSH
+    elif is_straight_flush(hand):
+        return Rank.STRAIGHT_FLUSH
+    elif is_four_of_a_kind(hand):
+        return Rank.FOUR_OF_A_KIND
+    elif is_full_house(hand):
+        return Rank.FULL_HOUSE
+    elif is_flush(hand):
+        return Rank.FLUSH
+    elif is_straight(hand):
+        return Rank.STRAIGHT
+    elif is_three_of_a_kind(hand):
+        return Rank.THREE_OF_A_KIND
+    elif is_two_pair(hand):
+        return Rank.TWO_PAIR
+    elif is_pair(hand):
+        return Rank.PAIR
+    else:
+        return Rank.HIGH_CARD