Bowling Game Kata

Game.php

<?php

namespace App;

class Game
{
    /**
     * The number of frames in a game.
     */
    const FRAMES_PER_GAME = 10;

    /**
     * All rolls for the game.
     *
     * @var array
     */
    protected array $rolls = [];

    /**
     * Roll the ball.
     *
     * @param  int  $pins
     * @return void
     */
    public function roll(int $pins): void
    {
        $this->rolls[] = $pins;
    }

    /**
     * Calculate the final score.
     *
     * @return int
     */
    public function score()
    {
        $score = 0;
        $roll = 0;

        foreach (range(1, self::FRAMES_PER_GAME) as $frame) {
            if ($this->isStrike($roll)) {
                $score += $this->pinCount($roll) + $this->strikeBonus($roll);

                $roll += 1;

                continue;
            }

            $score += $this->defaultFrameScore($roll);

            if ($this->isSpare($roll)) {
                $score += $this->spareBonus($roll);
            }

            $roll += 2;
        }

        return $score;
    }

    /**
     * Determine if the current roll was a strike.
     *
     * @param  int  $roll
     * @return bool
     */
    protected function isStrike(int $roll): bool
    {
        return $this->pinCount($roll) === 10;
    }

    /**
     * Determine if the current frame was a spare.
     *
     * @param  int  $roll
     * @return bool
     */
    protected function isSpare(int $roll): bool
    {
        return $this->defaultFrameScore($roll) === 10;
    }

    /**
     * Calculate the score for the frame.
     *
     * @param  int  $roll
     * @return int
     */
    protected function defaultFrameScore(int $roll): int
    {
        return $this->pinCount($roll) + $this->pinCount($roll + 1);
    }

    /**
     * Get the bonus for a strike.
     *
     * @param  int  $roll
     * @return int
     */
    protected function strikeBonus(int $roll): int
    {
        return $this->pinCount($roll + 1) + $this->pinCount($roll + 2);
    }

    /**
     * Get the bonus for a spare.
     *
     * @param  int  $roll
     * @return int
     */
    protected function spareBonus(int $roll): int
    {
        return $this->pinCount($roll + 2);
    }

    /**
     * Get the number of pins knocked down for the given roll.
     *
     * @param  int  $roll
     * @return int
     */
    protected function pinCount(int $roll): int
    {
        return $this->rolls[$roll];
    }
}

GameTest.php

<?php

use App\Game;
use PHPUnit\Framework\TestCase;

class GameTest extends TestCase
{
    /** @test */
    function it_scores_a_gutter_game_as_zero()
    {
        $game = new Game();

        foreach (range(1, 20) as $roll) {
            $game->roll(0);
        }

        $this->assertSame(0, $game->score());
    }

    /** @test */
    function it_scores_all_ones()
    {
        $game = new Game();

        foreach (range(1, 20) as $roll) {
            $game->roll(1);
        }

        $this->assertSame(20, $game->score());
    }

    /** @test */
    function it_awards_a_one_roll_bonus_for_every_spare()
    {
        $game = new Game();

        $game->roll(5);
        $game->roll(5); // spare

        $game->roll(8);

        foreach (range(1, 17) as $roll) {
            $game->roll(0);
        }

        $this->assertSame(26, $game->score());
    }

    /** @test */
    function it_awards_a_two_roll_bonus_for_every_strike()
    {
        $game = new Game();

        $game->roll(10); // strike

        $game->roll(5);
        $game->roll(2);

        foreach (range(1, 16) as $roll) {
            $game->roll(0);
        }

        $this->assertSame(24, $game->score());
    }

    /** @test */
    function a_spare_on_the_final_frame_grants_one_extra_ball()
    {
        $game = new Game();

        foreach (range(1, 18) as $roll) {
            $game->roll(0);
        }

        $game->roll(5);
        $game->roll(5); // spare

        $game->roll(5);

        $this->assertSame(15, $game->score());
    }

    /** @test */
    function a_strike_on_the_final_frame_grants_two_extra_balls()
    {
        $game = new Game();

        foreach (range(1, 18) as $roll) {
            $game->roll(0);
        }

        $game->roll(10); // strike

        $game->roll(10);
        $game->roll(10);

        $this->assertSame(30, $game->score());
    }

    /** @test */
    function it_scores_a_perfect_game()
    {
        $game = new Game();

        foreach (range(1, 12) as $roll) {
            $game->roll(10);
        }

        $this->assertSame(300, $game->score());
    }
}