Feat/split strategy

src/Domain/BasicStrategy.php

@@ -9,6 +9,38 @@ public function decide(Hand $hand, Card $dealerCard): Decision
         $value = $hand->value();
         $dealerValue = $dealerCard->numericValue();
 
+        if ($hand->isPair()) {
+            $rank = $hand->pairRank();
+
+            if ($rank === 'Ace' || $rank === '8') {
+                return Decision::Split;
+            }
+
+            if ($rank === '9' && !in_array($dealerValue, [7, 10, 11], true)) {
+                return Decision::Split;
+            }
+
+            if ($rank === '7' && $dealerValue >= 2 && $dealerValue <= 7) {
+                return Decision::Split;
+            }
+
+            if ($rank === '6' && $dealerValue >= 2 && $dealerValue <= 6) {
+                return Decision::Split;
+            }
+
+            if ($rank === '4' && $dealerValue >= 5 && $dealerValue <= 6) {
+                return Decision::Split;
+            }
+
+            if ($rank === '3' && $dealerValue >= 2 && $dealerValue <= 7) {
+                return Decision::Split;
+            }
+
+            if ($rank === '2' && $dealerValue >= 2 && $dealerValue <= 7) {
+                return Decision::Split;
+            }
+        }
+
         if ($hand->isSoft() && $value === 18) {
             if ($dealerValue >= 3 && $dealerValue <= 6) {
                 return Decision::Double;

src/Domain/Hand.php

@@ -57,4 +57,15 @@ public function isSoft(): bool
 
         return $aces > 0 && $total <= 21;
     }
+
+    public function isPair(): bool
+    {
+        return count($this->cards) === 2
+            && $this->cards[0]->rank() === $this->cards[1]->rank();
+    }
+
+    public function pairRank(): string
+    {
+        return $this->cards[0]->rank();
+    }
 }

tests/Domain/BasicStrategyTest.php

@@ -340,8 +340,8 @@ public function testHard8ShouldAlwaysHit(): void
         $strategy = new BasicStrategy();
 
         $hand = new Hand();
-        $hand->addCard(new Card('4', 'Hearts'));
-        $hand->addCard(new Card('4', 'Spades'));
+        $hand->addCard(new Card('5', 'Hearts'));
+        $hand->addCard(new Card('3', 'Spades'));
 
         $dealerCard = new Card('6', 'Diamonds');
 
@@ -386,4 +386,134 @@ public function testHard16AgainstDealer7ShouldHit(): void
 
         $this->assertSame(Decision::Hit, $strategy->decide($hand, $dealerCard));
     }
+
+    public function testPairOf8sShouldAlwaysSplit(): void
+    {
+        $strategy = new BasicStrategy();
+
+        $hand = new Hand();
+        $hand->addCard(new Card('8', 'Hearts'));
+        $hand->addCard(new Card('8', 'Spades'));
+
+        $dealerCard = new Card('6', 'Diamonds');
+
+        $this->assertSame(Decision::Split, $strategy->decide($hand, $dealerCard));
+    }
+
+    public function testPairOf9sAgainstDealer6ShouldSplit(): void
+    {
+        $strategy = new BasicStrategy();
+
+        $hand = new Hand();
+        $hand->addCard(new Card('9', 'Hearts'));
+        $hand->addCard(new Card('9', 'Spades'));
+
+        $dealerCard = new Card('6', 'Diamonds');
+
+        $this->assertSame(Decision::Split, $strategy->decide($hand, $dealerCard));
+    }
+
+    public function testPairOf9sAgainstDealer7ShouldStand(): void
+    {
+        $strategy = new BasicStrategy();
+
+        $hand = new Hand();
+        $hand->addCard(new Card('9', 'Hearts'));
+        $hand->addCard(new Card('9', 'Spades'));
+
+        $dealerCard = new Card('7', 'Diamonds');
+
+        $this->assertSame(Decision::Stand, $strategy->decide($hand, $dealerCard));
+    }
+
+    public function testPairOf7sAgainstDealer5ShouldSplit(): void
+    {
+        $strategy = new BasicStrategy();
+
+        $hand = new Hand();
+        $hand->addCard(new Card('7', 'Hearts'));
+        $hand->addCard(new Card('7', 'Spades'));
+
+        $dealerCard = new Card('5', 'Diamonds');
+
+        $this->assertSame(Decision::Split, $strategy->decide($hand, $dealerCard));
+    }
+
+    public function testPairOf6sAgainstDealer4ShouldSplit(): void
+    {
+        $strategy = new BasicStrategy();
+
+        $hand = new Hand();
+        $hand->addCard(new Card('6', 'Hearts'));
+        $hand->addCard(new Card('6', 'Spades'));
+
+        $dealerCard = new Card('4', 'Diamonds');
+
+        $this->assertSame(Decision::Split, $strategy->decide($hand, $dealerCard));
+    }
+
+    public function testPairOf4sAgainstDealer5ShouldSplit(): void
+    {
+        $strategy = new BasicStrategy();
+
+        $hand = new Hand();
+        $hand->addCard(new Card('4', 'Hearts'));
+        $hand->addCard(new Card('4', 'Spades'));
+
+        $dealerCard = new Card('5', 'Diamonds');
+
+        $this->assertSame(Decision::Split, $strategy->decide($hand, $dealerCard));
+    }
+
+    public function testPairOf3sAgainstDealer4ShouldSplit(): void
+    {
+        $strategy = new BasicStrategy();
+
+        $hand = new Hand();
+        $hand->addCard(new Card('3', 'Hearts'));
+        $hand->addCard(new Card('3', 'Spades'));
+
+        $dealerCard = new Card('4', 'Diamonds');
+
+        $this->assertSame(Decision::Split, $strategy->decide($hand, $dealerCard));
+    }
+
+    public function testPairOf2sAgainstDealer4ShouldSplit(): void
+    {
+        $strategy = new BasicStrategy();
+
+        $hand = new Hand();
+        $hand->addCard(new Card('2', 'Hearts'));
+        $hand->addCard(new Card('2', 'Spades'));
+
+        $dealerCard = new Card('4', 'Diamonds');
+
+        $this->assertSame(Decision::Split, $strategy->decide($hand, $dealerCard));
+    }
+
+    public function testPairOf5sShouldNotSplit(): void
+    {
+        $strategy = new BasicStrategy();
+
+        $hand = new Hand();
+        $hand->addCard(new Card('5', 'Hearts'));
+        $hand->addCard(new Card('5', 'Spades'));
+
+        $dealerCard = new Card('6', 'Diamonds');
+
+        $this->assertSame(Decision::Double, $strategy->decide($hand, $dealerCard));
+    }
+
+    public function testPairOf10sShouldNotSplit(): void
+    {
+        $strategy = new BasicStrategy();
+
+        $hand = new Hand();
+        $hand->addCard(new Card('10', 'Hearts'));
+        $hand->addCard(new Card('10', 'Spades'));
+
+        $dealerCard = new Card('6', 'Diamonds');
+
+        $this->assertSame(Decision::Stand, $strategy->decide($hand, $dealerCard));
+    }
 }

tests/Domain/HandTest.php

@@ -70,4 +70,31 @@ public function testHandWithAceCountedAs11IsSoft(): void
 
         $this->assertTrue($hand->isSoft());
     }
+
+    public function testHandWithTwoIdenticalRanksIsPair(): void
+    {
+        $hand = new Hand();
+        $hand->addCard(new Card('8', 'Hearts'));
+        $hand->addCard(new Card('8', 'Spades'));
+
+        $this->assertTrue($hand->isPair());
+    }
+
+    public function testHandWithDifferentRanksIsNotPair(): void
+    {
+        $hand = new Hand();
+        $hand->addCard(new Card('8', 'Hearts'));
+        $hand->addCard(new Card('9', 'Spades'));
+
+        $this->assertFalse($hand->isPair());
+    }
+
+    public function testPairRankReturnsCardRank(): void
+    {
+        $hand = new Hand();
+        $hand->addCard(new Card('8', 'Hearts'));
+        $hand->addCard(new Card('8', 'Spades'));
+
+        $this->assertSame('8', $hand->pairRank());
+    }
 }