my PR (I had no time to think about the PR title, sorry :P)

phpunit.xml

@@ -8,6 +8,7 @@
          beStrictAboutOutputDuringTests="true"
          beStrictAboutTodoAnnotatedTests="true"
          verbose="true"
+         testdox="true"
          colors="true">
     <testsuites>
         <testsuite name="default">

src/Game.php

@@ -0,0 +1,49 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ClansOfCaledonia;
+
+use ClansOfCaledonia\Good\Grain;
+use ClansOfCaledonia\Good\Milk;
+use ClansOfCaledonia\Good\Wool;
+
+final class Game
+{
+    const GOODS = [ // TODO: Improve this
+        'Milk',
+        'Wool',
+        'Grain',
+    ];
+
+    public static function main(Pound $money): void
+    {
+        $priceBuilder = new PriceListBuilder();
+
+        $market = (new Market)
+            ->withPriceList(Milk::name(), $priceBuilder->milkPrices())
+            ->withPriceList(Wool::name(), $priceBuilder->woolPrices())
+            ->withPriceList(Grain::name(), $priceBuilder->grainPrices());
+
+        $player = new Player($money, $market);
+        while (true) {
+            echo sprintf('You have %i pounds', $player->money());
+            $goodName = readline(sprintf('What do you want to buy now? (%s)', implode(',', self::GOODS)));
+            $amount = (int)readline('How many pounds?');
+            $player->buy(new Unit($amount), Good::byName($goodName));
+            static::printMarket($market);
+            sleep(1);
+        }
+    }
+
+    private static function printMarket(Market $market)
+    {
+        foreach($market->allPriceList() as $goodName => $priceList){
+            echo $goodName.PHP_EOL;
+            foreach($priceList as $price) {
+                // display the table
+            }
+            echo PHP_EOL;
+        }
+    }
+}

src/Good.php

@@ -1,11 +1,45 @@
 <?php declare(strict_types=1);
+
 namespace ClansOfCaledonia;
 
+use ClansOfCaledonia\Good\Grain;
+use ClansOfCaledonia\Good\Milk;
+use ClansOfCaledonia\Good\Wool;
+
 abstract class Good
 {
+    public static function name(): string
+    {
+        return static::class;
+    }
+
     public static function milk(): self
     {
-        return new Milk;
+        return new Milk();
+    }
+
+    public static function wool(): self
+    {
+        return new Wool();
+    }
+
+    public static function grain(): self
+    {
+        return new Grain();
+    }
+
+    public static function byName(string $goodName)
+    {
+        switch ($goodName){
+            case Milk::name():
+                return self::milk();
+            case Wool::name():
+                return self::wool();
+            case Grain::name():
+                return self::grain();
+        }
+
+        throw new \Exception('Good Unknown');
     }
 
     public function isMilk(): bool

src/Good/Grain.php

@@ -0,0 +1,9 @@
+<?php declare(strict_types=1);
+
+namespace ClansOfCaledonia\Good;
+
+use ClansOfCaledonia\Good;
+
+final class Grain extends Good
+{
+}

src/Good/Milk.php

@@ -0,0 +1,18 @@
+<?php declare(strict_types=1);
+
+namespace ClansOfCaledonia\Good;
+
+use ClansOfCaledonia\Good;
+
+final class Milk extends Good
+{
+    public static function name(): string
+    {
+        return 'Milk';
+    }
+
+    public function isMilk(): bool
+    {
+        return true;
+    }
+}

src/Good/Wool.php

@@ -0,0 +1,9 @@
+<?php declare(strict_types=1);
+
+namespace ClansOfCaledonia\Good;
+
+use ClansOfCaledonia\Good;
+
+final class Wool extends Good
+{
+}

src/Market.php

@@ -1,18 +1,43 @@
 <?php declare(strict_types=1);
+
 namespace ClansOfCaledonia;
 
 final class Market
 {
-    public function priceFor(Good $milk): Pound
+    /** @var array<string,PriceList> */
+    private $prices;
+
+    public function __construct()
     {
-        return new Pound(5);
+        $this->prices = [];
+    }
+
+    public function withPriceList(string $goodName, PriceList $priceList): self
+    {
+        $this->prices[$goodName] = $priceList;
+
+        return $this;
+    }
+
+    public function priceFor(Good $good): Pound
+    {
+        return $this->prices[$good->name()]->current();
     }
 
     public function sellTo(Offer $offer): Pound
     {
-        return new Pound(
-            $offer->amount()->amount() *
-            $this->priceFor($offer->good())->amount()
-        );
+        $good = $offer->good();
+        $unit = $offer->amount();
+        $payment = $this->priceFor($good)->multiply($unit->amount());
+        $this->adjustPrice($good, $unit);
+
+        return $payment;
+    }
+
+    private function adjustPrice(Good $good, Unit $unit)
+    {
+        /** @var PriceList $priceList */
+        $priceList = $this->prices[$good->name()];
+        $priceList->moveTo($unit);
     }
 }

src/Player.php

@@ -0,0 +1,29 @@
+<?php declare(strict_types=1);
+
+namespace ClansOfCaledonia;
+
+final class Player
+{
+    /** @var Pound */
+    private $money;
+
+    /** @var Market */
+    private $market;
+
+    public function __construct(Pound $money, Market $market)
+    {
+        $this->money = $money;
+        $this->market = $market;
+    }
+
+    public function buy(Unit $unit, Good $good): void
+    {
+        $payment = $this->market->sellTo(new Offer($unit, $good));
+        $this->money = $this->money->minus($payment->amount());
+    }
+
+    public function money(): Pound
+    {
+        return $this->money;
+    }
+}

src/Pound.php

@@ -1,4 +1,5 @@
 <?php declare(strict_types=1);
+
 namespace ClansOfCaledonia;
 
 final class Pound
@@ -17,4 +18,14 @@ public function amount(): int
     {
         return $this->amount;
     }
+
+    public function multiply(int $factor): Pound
+    {
+        return new Pound($this->amount * $factor);
+    }
+
+    public function minus(int $number): Pound
+    {
+        return new Pound($this->amount - $number);
+    }
 }

src/PriceList.php

@@ -1,4 +1,5 @@
 <?php declare(strict_types=1);
+
 namespace ClansOfCaledonia;
 
 final class PriceList
@@ -11,23 +12,30 @@ final class PriceList
     /**
      * @var int
      */
-    private $position = 3;
+    private $position;
 
-    public static function fromList(Pound ...$pounds): self
+    public static function fromList(int $initPosition, Pound ...$pounds): self
     {
-        return new self($pounds);
+        return new self($initPosition, $pounds);
     }
 
     /**
+     * @param int $initPosition
      * @param Pound[] $prices
      */
-    private function __construct(array $prices)
+    private function __construct(int $initPosition, array $prices)
     {
+        $this->position = $initPosition;
         $this->prices = $prices;
     }
 
     public function current(): Pound
     {
         return $this->prices[$this->position];
     }
+
+    public function moveTo(Unit $unit): void
+    {
+        $this->position += $unit->amount();
+    }
 }

src/PriceListBuilder.php

@@ -1,11 +1,13 @@
 <?php declare(strict_types=1);
+
 namespace ClansOfCaledonia;
 
 final class PriceListBuilder
 {
     public function milkPrices(): PriceList
     {
         return PriceList::fromList(
+            $initPosition = 3,
             new Pound(3),
             new Pound(4),
             new Pound(5),
@@ -18,4 +20,38 @@ public function milkPrices(): PriceList
             new Pound(8)
         );
     }
+
+    public function woolPrices(): PriceList
+    {
+        return PriceList::fromList(
+            $initPosition = 3,
+            new Pound(3),
+            new Pound(3),
+            new Pound(4),
+            new Pound(4),
+            new Pound(5),
+            new Pound(5),
+            new Pound(6),
+            new Pound(6),
+            new Pound(7),
+            new Pound(8)
+        );
+    }
+
+    public function grainPrices(): PriceList
+    {
+        return PriceList::fromList(
+            $initPosition = 3,
+            new Pound(3),
+            new Pound(3),
+            new Pound(4),
+            new Pound(5),
+            new Pound(6),
+            new Pound(6),
+            new Pound(7),
+            new Pound(7),
+            new Pound(8),
+            new Pound(8)
+        );
+    }
 }

src/autoload.php

@@ -9,10 +9,13 @@ function($class) {
             $classes = array(
                 'clansofcaledonia\\exception' => '/Exception.php',
                 'clansofcaledonia\\good' => '/Good.php',
+                'clansofcaledonia\\good\\grain' => '/Good/Grain.php',
+                'clansofcaledonia\\good\\milk' => '/Good/Milk.php',
+                'clansofcaledonia\\good\\wool' => '/Good/Wool.php',
                 'clansofcaledonia\\market' => '/Market.php',
-                'clansofcaledonia\\milk' => '/Milk.php',
                 'clansofcaledonia\\offer' => '/Offer.php',
                 'clansofcaledonia\\outofrangeexception' => '/OutOfRangeException.php',
+                'clansofcaledonia\\player' => '/Player.php',
                 'clansofcaledonia\\pound' => '/Pound.php',
                 'clansofcaledonia\\pricelist' => '/PriceList.php',
                 'clansofcaledonia\\pricelistbuilder' => '/PriceListBuilder.php',

tests/GoodTest.php → tests/Good/GoodTest.php

@@ -1,6 +1,8 @@
 <?php declare(strict_types=1);
-namespace ClansOfCaledonia;
 
+namespace ClansOfCaledonia\Good;
+
+use ClansOfCaledonia\Good;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -15,4 +17,11 @@ public function testCanBeMilk(): void
 
         $this->assertTrue($milk->isMilk());
     }
+
+    public function testCanNotBeMilk(): void
+    {
+        $grain = Good::grain();
+
+        $this->assertFalse($grain->isMilk());
+    }
 }