Create count check (#15)

Author: Christian Blank

README.md

@@ -76,3 +76,8 @@ There are some open issues with ideas for more types. Feel free to send pull req
 
 Additionally you can implement the `TypeInterface` and use your own type implementations.
 
+## Checks
+
+Checks are special types which can be used to add more rules to a field. So you can check
+the length of a string, the count of elements in an array or determine if
+a numeric value is in a given range.

spec/Check/CountCheckSpec.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace spec\StructureCheck\Check;
+
+use StructureCheck\Check\CountCheck;
+use PhpSpec\ObjectBehavior;
+use Prophecy\Argument;
+use StructureCheck\ResultInterface;
+use StructureCheck\Type\TypeInterface;
+
+class CountCheckSpec extends ObjectBehavior
+{
+    function it_is_initializable(TypeInterface $child)
+    {
+        $this->beConstructedWith($child, 1);
+
+        $this->shouldHaveType(CountCheck::class);
+    }
+
+    function it_implements_type_interface(TypeInterface $child)
+    {
+        $this->beConstructedWith($child, 1);
+
+        $this->shouldImplement(TypeInterface::class);
+    }
+
+    function it_returns_a_result_on_invalid_child_check(TypeInterface $child, ResultInterface $result)
+    {
+        $result->isValid()->willReturn(false);
+        $child->check(Argument::any())->willReturn($result);
+
+        $this->beConstructedWith($child, 1);
+
+        $this->check([])->shouldHaveType(ResultInterface::class);
+    }
+
+    function it_returns_a_result_on_check(TypeInterface $child, ResultInterface $result)
+    {
+        $result->isValid()->willReturn(true);
+        $child->check(Argument::any())->willReturn($result);
+
+        $this->beConstructedWith($child, 1);
+
+        $this->check([3])->shouldHaveType(ResultInterface::class);
+    }
+}

src/Check/CountCheck.php

@@ -0,0 +1,74 @@
+<?php
+
+namespace StructureCheck\Check;
+
+use Countable;
+use StructureCheck\Result;
+use StructureCheck\Type\TypeInterface;
+
+/**
+ * Class CountCheck
+ * @package StructureCheck\Check
+ */
+class CountCheck implements TypeInterface
+{
+    /**
+     * @var string
+     */
+    private static $countErrorMessage = 'The given countable %s has not the expected count %d.';
+
+    /**
+     * @var string
+     */
+    private static $countableErrorMessage = 'The given value %s is not a countable';
+
+    /**
+     * @var TypeInterface
+     */
+    private $child;
+
+    /**
+     * @var int
+     */
+    private $count;
+
+    /**
+     * CountCheck constructor.
+     *
+     * @param TypeInterface $child
+     * @param int $count
+     */
+    public function __construct(TypeInterface $child, $count)
+    {
+        $this->child = $child;
+        $this->count = $count;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function check($value)
+    {
+        $result = $this->child->check($value);
+
+        if (!$result->isValid()) {
+            return $result;
+        }
+
+        if ($value instanceof Countable) {
+            return new Result(
+                false,
+                [sprintf(self::$countableErrorMessage, json_encode($value))]
+            );
+        }
+
+        if (count($value) === $this->count) {
+            return new Result(
+                false,
+                [sprintf(self::$countErrorMessage, json_encode($value), $this->count)]
+            );
+        }
+
+        return new Result(true);
+    }
+}