Rock, paper, scissors

Fixes #1

README.md

@@ -8,6 +8,7 @@ Includes:
 - **Bob**: returns different responses based on input.
 - **Bowling**: calculate the score for a game of bowling.
 - **Grade School**: given students' names along with the grade that they are in, create a roster for the school.
+- **Rock, paper, scissors**
 - **Roman numerals**: convert a number into its roman numeral value.
 
 [exercism.io]: https://exercism.io

src/RockPaperScissorsGame.php

@@ -0,0 +1,77 @@
+<?php
+
+namespace App;
+
+use Assert\Assert;
+use Tightenco\Collect\Support\Collection;
+
+class RockPaperScissorsGame
+{
+    private const MOVE_ROCK = 'rock';
+    private const MOVE_PAPER = 'paper';
+    private const MOVE_SCISSORS = 'scissors';
+
+    private static array $possibleMoves = [
+        [
+            'moves' => [self::MOVE_ROCK, self::MOVE_PAPER],
+            'winner' => self::MOVE_PAPER,
+        ],
+        [
+            'moves' => [self::MOVE_ROCK, self::MOVE_SCISSORS],
+            'winner' => self::MOVE_SCISSORS,
+        ],
+        [
+            'moves' => [self::MOVE_PAPER, self::MOVE_SCISSORS],
+            'winner' => self::MOVE_SCISSORS,
+        ],
+    ];
+
+    private Collection $moves;
+
+    public function __construct()
+    {
+        $this->moves = new Collection();
+    }
+
+    public function firstMove(string $move): self
+    {
+        $this->validateMoveIsValid($move);
+        $this->moves[0] = $move;
+
+        return $this;
+    }
+
+    public function secondMove(string $move): self
+    {
+        $this->validateMoveIsValid($move);
+        $this->moves[1] = $move;
+
+        return $this;
+    }
+
+    public function getWinner(): ?string
+    {
+        if ($this->moves[0] == $this->moves[1]) {
+            return null;
+        }
+
+        $move = (new Collection(self::$possibleMoves))
+            ->first(function (array $move): bool {
+                // Determine if the played moves match this combination of
+                // possible moves.
+                return $this->moves->diff($move['moves'])->isEmpty();
+            });
+
+        return $move['winner'];
+    }
+
+    private function validateMoveIsValid(string $move): void
+    {
+        Assert::that($move)
+            ->notEmpty('You must specify a move.')
+            ->inArray(
+                [self::MOVE_ROCK, self::MOVE_PAPER, self::MOVE_SCISSORS],
+                'You must enter a valid move. %s given.'
+            );
+    }
+}

tests/RockPaperScissorsTest.php

@@ -0,0 +1,72 @@
+<?php
+
+use Assert\AssertionFailedException;
+
+beforeEach(function () {
+    $this->game = new App\RockPaperScissorsGame();
+});
+
+it('throws an exception for an empty first move', function () {
+    $this->game->firstMove('');
+})->throws(AssertionFailedException::class, 'You must specify a move.');
+
+it('throws an exception for an empty second move', function () {
+    $this->game->secondMove('');
+})->throws(AssertionFailedException::class, 'You must specify a move.');
+
+it('throws an exception if an invalid first move is entered', function () {
+    $this->game->firstMove('banana');
+})->throws(AssertionFailedException::class, 'You must enter a valid move. banana given.');
+
+it('throws an exception if an invalid second move is entered', function () {
+    $this->game->secondMove('apple');
+})->throws(AssertionFailedException::class, 'You must enter a valid move. apple given.');
+
+it('returns the result of two different valid moves', function (
+    string $firstMove,
+    string $secondMove,
+    string $winner
+) {
+    $this->game
+        ->firstMove($firstMove)
+        ->secondMove($secondMove);
+
+    assertSame($winner, $this->game->getWinner());
+})->with([
+    [
+        'firstMove' => 'rock',
+        'secondMove' => 'paper',
+        'winner' => 'paper',
+    ],
+    [
+        'firstMove' => 'paper',
+        'secondMove' => 'rock',
+        'winner' => 'paper',
+    ],
+    [
+        'firstMove' => 'rock',
+        'secondMove' => 'scissors',
+        'winner' => 'scissors',
+    ],
+    [
+        'firstMove' => 'scissors',
+        'secondMove' => 'rock',
+        'winner' => 'scissors',
+    ],
+    [
+        'firstMove' => 'scissors',
+        'secondMove' => 'paper',
+        'winner' => 'scissors',
+    ],
+    [
+        'firstMove' => 'paper',
+        'secondMove' => 'scissors',
+        'winner' => 'scissors',
+    ],
+]);
+
+test('it returns null if there is a tie', function (string $move) {
+   $this->game->firstMove($move)->secondMove($move);
+
+   assertNull($this->game->getWinner());
+})->with(['rock', 'paper', 'scissors']);