feat: Get hand rank

Method to get rank of a given hand.

5 files changed, 141 insertions, 1 deletions

diff --git a/poker/constants.py b/poker/constants.py
index 04a8b34..e0a7348 100644
--- a/poker/constants.py
+++ b/poker/constants.py
@@ -3,6 +3,21 @@ from enum import IntEnum, auto
 from poker.utils.enum import AutoName
 
 
+class Rank(IntEnum):
+    """Poker rank enum."""
+
+    ROYAL_FLUSH = 1
+    STRAIGHT_FLUSH = 2
+    FOUR_OF_A_KIND = 3
+    FULL_HOUSE = 4
+    FLUSH = 5
+    STRAIGHT = 6
+    THREE_OF_A_KIND = 7
+    TWO_PAIR = 8
+    PAIR = 9
+    HIGH_CARD = 10
+
+
 class Suit(AutoName):
     """Card suit enum."""
 
@@ -15,7 +30,6 @@ class Suit(AutoName):
 class Value(IntEnum):
     """Card value enum."""
 
-    ACE = 1
     TWO = 2
     THREE = 3
     FOUR = 4
@@ -28,3 +42,12 @@ class Value(IntEnum):
     JACK = 11
     QUEEN = 12
     KING = 13
+    ACE = 14
+
+    def __str__(self) -> str:
+        """Return string representation."""
+        if self.value in [1, 11, 12, 13]:
+            out: str = self.name.lower()
+        else:
+            out = str(self.value)
+        return out
diff --git a/poker/models.py b/poker/models.py
index 1d6af05..bbb474c 100644
--- a/poker/models.py
+++ b/poker/models.py
@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+from collections import Counter
+
 from pydantic import BaseModel, validator
 
 from poker.constants import Rank, Suit, Value
@@ -43,6 +45,11 @@ class Hand(BaseModel):
             raise ValueError("Hand must have five cards.")
         return cards
 
+    @property
+    def value_counts(self) -> list[tuple[Value, int]]:
+        """Return count of each card value in hand."""
+        return Counter([card.value for card in self.cards]).most_common()
+
 
 class RankedHand(Hand):
     """Ranked hand  domain model class."""
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