From 268ee0cbfa4fba5ddc46a7b23101a044501ad6bc Mon Sep 17 00:00:00 2001
From: Niklas Ekman <nikl.ekman@gmail.com>
Date: Fri, 23 Feb 2018 19:48:58 +0700
Subject: [PATCH 1/5] Add new testcase.

---
 tests/LuhnAlgorithmTest.php | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tests/LuhnAlgorithmTest.php b/tests/LuhnAlgorithmTest.php
index b32dd50..0144561 100644
--- a/tests/LuhnAlgorithmTest.php
+++ b/tests/LuhnAlgorithmTest.php
@@ -52,6 +52,7 @@ public function provideIsValid_success() {
 			["410321-9202", true],
 			["410321 - 9202", true],
 			[4103219202, true],
+			[31997233700020, true],
 		];
 	}
 
@@ -79,6 +80,7 @@ public function provideCalcCheckDigit_success() {
 		return [
 			[12345, 5],
 			[410321920, 2],
+			[3199723370002, 0],
 		];
 	}
 }

From 33d3d0aa7c411eb5adab26559ba787c83276c799 Mon Sep 17 00:00:00 2001
From: Niklas Ekman <nikl.ekman@gmail.com>
Date: Mon, 26 Feb 2018 18:40:39 +0100
Subject: [PATCH 2/5] New implementation.

---
 .gitignore                              |  1 +
 README.md                               | 19 ++-----
 src/Contract/LuhnAlgorithmInterface.php | 12 ++--
 src/LuhnAlgorithm.php                   | 76 +++++++++++++------------
 src/LuhnAlgorithmFactory.php            |  1 -
 tests/LuhnAlgorithmTest.php             | 14 ++---
 6 files changed, 60 insertions(+), 63 deletions(-)

diff --git a/.gitignore b/.gitignore
index f2a1ce6..7044502 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 index.php
 nbproject/
+.idea/
 
 # Created by http://www.gitignore.io
 
diff --git a/README.md b/README.md
index 974d75a..e4badb9 100644
--- a/README.md
+++ b/README.md
@@ -3,12 +3,13 @@
 [![Build Status](https://travis-ci.org/Ekman/Luhn-Algorithm.svg?branch=master)](https://travis-ci.org/Ekman/Luhn-Algorithm)
 
 This is an implementation of the Luhn Algorithm in PHP. The Luhn Algorithm is
-used to validate things like credit cards and national identifcation numbers.
-More information on the algorithm can be found at [Wikipedia](http://en.wikipedia.org/wiki/Luhn_algorithm)
+used to validate things like credit cards and national identification numbers.
+More information on the algorithm can be found at [Wikipedia](http://en.wikipedia.org/wiki/Luhn_algorithm).
 
 ## Installation
 
-Can be installed using composer:
+Install with [Composer](https://getcomposer.org/):
+
 ```bash
 composer require nekman/luhn-algorithm
 ```
@@ -26,15 +27,7 @@ if ($luhn->isValid(123456789)) {
 	// Number is valid.
 }
 
-$checkSum = $luhn->calcCheckSum(123456789);
+$checkSum = $luhn->calcChecksum(123456789);
 
 $checkDigit = $luhn->calcCheckDigit(123456789);
-```
-
-## Changelog
-
-* 4.0.0 - Rewrite of the implementation.
-* 3.0.0 - Completely restructured the interface of the library. 
-* 2.0.1 - Fixed typos in interface.
-* 2.0.0 - Added namespace.
-* 1.0.0 - Initial release.
+```
\ No newline at end of file
diff --git a/src/Contract/LuhnAlgorithmInterface.php b/src/Contract/LuhnAlgorithmInterface.php
index 83388d4..bf20512 100644
--- a/src/Contract/LuhnAlgorithmInterface.php
+++ b/src/Contract/LuhnAlgorithmInterface.php
@@ -34,33 +34,33 @@ interface LuhnAlgorithmInterface {
     /**
      * Determine if a number is valid according to the Luhn Algorithm.
      * 
-     * @param string $input The number to validate.
+     * @param string $number The number to validate.
      * 
      * @return bool true if number is valid, false otherwise.
      * 
      * @throws \InvalidArgumentException If the input is invalid.
      */
-    public function isValid(string $input): bool;
+    public function isValid(string $number): bool;
 
     /**
      * Calculate the check digit for an input.
      * 
-     * @param int $input The input to calculate the check digit for.
+     * @param int $numberWithoutCheckDigit The number, without check digit, to calculate the check digit for.
      * 
      * @return int The check digit.
      * 
      * @throws \InvalidArgumentException If the input is invalid.
      */
-    public function calcCheckDigit(int $input): int;
+    public function calcCheckDigit(int $numberWithoutCheckDigit): int;
 
     /**
      * Calulates the checksum for number.
      * 
-     * @param int $input The number to calculate the checksum for.
+     * @param int $numberWithoutCheckDigit The number, without check digit, to calculate the checksum for.
      * 
      * @return int The checksum.
      * 
      * @throws \InvalidArgumentException If the input is invalid.
      */
-    public function calcChecksum(int $input): int;
+    public function calcChecksum(int $numberWithoutCheckDigit): int;
 }
diff --git a/src/LuhnAlgorithm.php b/src/LuhnAlgorithm.php
index 10e7766..f8dcd4a 100644
--- a/src/LuhnAlgorithm.php
+++ b/src/LuhnAlgorithm.php
@@ -28,66 +28,70 @@
 use Nekman\LuhnAlgorithm\Contract\LuhnAlgorithmInterface;
 
 /**
- * Handles the Luhn Algorithm.
- * 
- * @link http://en.wikipedia.org/wiki/Luhn_algorithm 
+ * {@inheritdoc}
  */
 class LuhnAlgorithm implements LuhnAlgorithmInterface {
 	/**
 	 * {@inheritDoc}
 	 */
-	public function isValid(string $input): bool {
+	public function isValid(string $number): bool {
 		// Remove everything except digits from the input.
-		$number = (int) preg_replace("/[^\d]/", "", $input);
-		
-		$checksum = $this->calcChecksum($number);
+		$number = preg_replace("/[^\d]/", "", $number);
+		$nDigits = strlen($number);
+        $checkDigit = $number[$nDigits - 1];
+
+        // Remove the last digit of number.
+        $number = (int) $number;
+        $numberWithoutCheckDigit = (int) ($number / 10);
+
+        $checksum = $this->calcChecksum($numberWithoutCheckDigit);
+        $sum = $checksum + $checkDigit;
 
 		// If the checksum  is divisible by 10 it is valid
-		return ($checksum % 10) === 0;
+		return ($sum % 10) === 0;
 	}
 
 	/**
 	 * {@inheritDoc}
 	 */
-	public function calcCheckDigit(int $input): int {
-		$checkSum = (string) $this->calcChecksum($input . 0);
+	public function calcCheckDigit(int $numberWithoutCheckDigit): int {
+		$checksum = (string) $this->calcChecksum($numberWithoutCheckDigit);
+		$nDigits = strlen($checksum);
 		
-		// Get the last digit of the checksum
-		$checkDigit = (int) $checkSum[strlen($checkSum) - 1];
+		// Get the last digit of the checksum.
+		$checkDigit = (int) $checksum[$nDigits - 1];
 
-		// If the checkdigit is not 0, then subtract the  value from 10
-		return $checkDigit === 0 ? $checkDigit : 10 - $checkDigit;
+		// If the check digit is not 0, then subtract the value from 10.
+		return $checkDigit === 0
+            ? $checkDigit
+            : 10 - $checkDigit;
 	}
 
 	/**
 	 * {@inheritDoc}
 	 */
-	public function calcChecksum(int $input): int {
-		$input = (string) $input;
-		$length = strlen($input);
-
-		$checkSum = 0;
+	public function calcChecksum(int $numberWithoutCheckDigit): int {
+		$numberWithoutCheckDigit = (string) $numberWithoutCheckDigit;
+		$nDigits = strlen($numberWithoutCheckDigit);
+		$checksum = 0;
+		$parity = $nDigits % 2;
 
-		// Start at the next last digit
-		for ($i = $length - 2; $i >= 0; $i -= 2) {
-			// Multiply number with 2
-			$tmp = (int) ($input[$i]) * 2;
+		for ($i = 0; $i < $nDigits; $i++) {
+		    $digit = (int) $numberWithoutCheckDigit[$i];
 
-			// If a 2 digit number, split and add togheter
-			if ($tmp > 9) {
-				$tmp = ($tmp / 10) + ($tmp % 10);
-			}
+		    // Every other digit, starting from the leftmost,
+            // shall be doubled.
+		    if (($i % 2) !== $parity) {
+		        $digit *= 2;
 
-			// Sum it upp
-			$checkSum += $tmp;
-		}
+                if ($digit > 9) {
+                    $digit -= 9;
+                }
+            }
 
-		// Start at the next last digit
-		for ($i = $length - 1; $i >= 0; $i -= 2) {
-			// Sum it upp
-			$checkSum += (int) $input[$i];
-		}
+            $checksum += $digit;
+        }
 
-		return $checkSum;
+		return $checksum;
 	}
 }
diff --git a/src/LuhnAlgorithmFactory.php b/src/LuhnAlgorithmFactory.php
index 17eeb13..d08a4a1 100644
--- a/src/LuhnAlgorithmFactory.php
+++ b/src/LuhnAlgorithmFactory.php
@@ -26,7 +26,6 @@
 namespace Nekman\LuhnAlgorithm;
 
 use Nekman\LuhnAlgorithm\Contract\LuhnAlgorithmInterface;
-use Nekman\LuhnAlgorithm\LuhmAlgorithm;
 
 /**
  * Factory for creating implementations of the Luhn Algorithm.
diff --git a/tests/LuhnAlgorithmTest.php b/tests/LuhnAlgorithmTest.php
index 0144561..21b2b84 100644
--- a/tests/LuhnAlgorithmTest.php
+++ b/tests/LuhnAlgorithmTest.php
@@ -32,25 +32,25 @@ class LuhnAlgorithmTest extends TestCase {
 	/**
 	 * @var LuhnAlgorithm
 	 */
-	private $object;
+	private $luhn;
 
 	public function setUp() {
 		parent::setUp();
 		
-		$this->object = new LuhnAlgorithm();
+		$this->luhn = new LuhnAlgorithm();
 	}
 
 	/**
 	 * @dataProvider provideIsValid_success
 	 */
 	public function testIsValid_success($number, $expected) {
-		$this->assertEquals($expected, $this->object->isValid($number));
+		$this->assertEquals($expected, $this->luhn->isValid($number));
 	}
 
 	public function provideIsValid_success() {
 		return [
 			["410321-9202", true],
-			["410321 - 9202", true],
+			[123455, true],
 			[4103219202, true],
 			[31997233700020, true],
 		];
@@ -60,12 +60,12 @@ public function provideIsValid_success() {
 	 * @dataProvider provideCalcChecksum_success
 	 */
 	public function testCalcChecksum_success($number, $expected) {
-		$this->assertEquals($expected, $this->object->calcChecksum($number));
+		$this->assertEquals($expected, $this->luhn->calcChecksum($number));
 	}
 
 	public function provideCalcChecksum_success() {
 		return [
-			[4103219202, 30],
+			[3199723370002, 50],
 		];
 	}
 
@@ -73,7 +73,7 @@ public function provideCalcChecksum_success() {
 	 * @dataProvider provideCalcCheckDigit_success
 	 */
 	public function testCalcCheckDigit_success($number, $expected) {
-		$this->assertEquals($expected, $this->object->calcCheckDigit($number));
+		$this->assertEquals($expected, $this->luhn->calcCheckDigit($number));
 	}
 
 	public function provideCalcCheckDigit_success() {

From 71dd3bd1db9e927da21b6f905a9e09d589c6b1ca Mon Sep 17 00:00:00 2001
From: Niklas Ekman <nikl.ekman@gmail.com>
Date: Mon, 26 Feb 2018 19:53:47 +0100
Subject: [PATCH 3/5] Add class for describing a number.

---
 .travis.yml                             |   1 -
 README.md                               |  15 +++-
 composer.json                           |   2 +-
 src/Contract/LuhnAlgorithmInterface.php |  32 ++++----
 src/Contract/NumberInterface.php        |  46 +++++++++++
 src/LuhnAlgorithm.php                   |  35 ++++-----
 src/Number.php                          | 100 ++++++++++++++++++++++++
 tests/LuhnAlgorithmTest.php             |  16 ++--
 tests/NumberTest.php                    |  48 ++++++++++++
 9 files changed, 243 insertions(+), 52 deletions(-)
 create mode 100644 src/Contract/NumberInterface.php
 create mode 100644 src/Number.php
 create mode 100644 tests/NumberTest.php

diff --git a/.travis.yml b/.travis.yml
index 678b85e..30db937 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,5 @@
 language: php
 php:
-  - '7.0'
   - '7.1'
   - '7.2'
 before_script: composer install
diff --git a/README.md b/README.md
index e4badb9..0edc3af 100644
--- a/README.md
+++ b/README.md
@@ -20,14 +20,21 @@ Use the class like this:
 
 ```php
 use Nekman\LuhnAlgorithm\LuhnAlgorithmFactory;
+use Nekman\LuhnAlgorithm\Number;
 
 $luhn = LuhnAlgorithmFactory::create();
 
-if ($luhn->isValid(123456789)) {
-	// Number is valid.
+// Validate a credit card number entered in a form.
+$ccNumber = Number::fromString($creditCard);
+if ($luhn->isValid($ccNumber)) {
+	// Credit card number is valid.
 }
 
-$checkSum = $luhn->calcChecksum(123456789);
+// These methods are used internally by the library. You're free
+// to make use of them as well.
+$number = new Number(12345);
 
-$checkDigit = $luhn->calcCheckDigit(123456789);
+$checksum = $luhn->calcChecksum($number);
+
+$checkDigit = $luhn->calcCheckDigit($number);
 ```
\ No newline at end of file
diff --git a/composer.json b/composer.json
index 239e734..30db7b6 100644
--- a/composer.json
+++ b/composer.json
@@ -31,7 +31,7 @@
 		}
 	},
 	"require": {
-		"php": "^7.0"
+		"php": "^7.1"
 	},
 	"require-dev": {
 		"phpunit/phpunit": "^6.5"
diff --git a/src/Contract/LuhnAlgorithmInterface.php b/src/Contract/LuhnAlgorithmInterface.php
index bf20512..455604f 100644
--- a/src/Contract/LuhnAlgorithmInterface.php
+++ b/src/Contract/LuhnAlgorithmInterface.php
@@ -33,34 +33,30 @@
 interface LuhnAlgorithmInterface {
     /**
      * Determine if a number is valid according to the Luhn Algorithm.
-     * 
-     * @param string $number The number to validate.
-     * 
+     *
+     * @param NumberInterface $number The number to validate.
+     *
      * @return bool true if number is valid, false otherwise.
-     * 
-     * @throws \InvalidArgumentException If the input is invalid.
      */
-    public function isValid(string $number): bool;
+    public function isValid(NumberInterface $number): bool;
 
     /**
      * Calculate the check digit for an input.
-     * 
-     * @param int $numberWithoutCheckDigit The number, without check digit, to calculate the check digit for.
-     * 
+     *
+     * @param NumberInterface $number The number, without check digit, to calculate the check digit for.
+     *
      * @return int The check digit.
-     * 
-     * @throws \InvalidArgumentException If the input is invalid.
+     *
      */
-    public function calcCheckDigit(int $numberWithoutCheckDigit): int;
+    public function calcCheckDigit(NumberInterface $number): int;
 
     /**
      * Calulates the checksum for number.
-     * 
-     * @param int $numberWithoutCheckDigit The number, without check digit, to calculate the checksum for.
-     * 
+     *
+     * @param NumberInterface $number The number, without check digit, to calculate the checksum for.
+     *
      * @return int The checksum.
-     * 
-     * @throws \InvalidArgumentException If the input is invalid.
+     *
      */
-    public function calcChecksum(int $numberWithoutCheckDigit): int;
+    public function calcChecksum(NumberInterface $number): int;
 }
diff --git a/src/Contract/NumberInterface.php b/src/Contract/NumberInterface.php
new file mode 100644
index 0000000..210b65f
--- /dev/null
+++ b/src/Contract/NumberInterface.php
@@ -0,0 +1,46 @@
+<?php
+
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Niklas Ekman
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+namespace Nekman\LuhnAlgorithm\Contract;
+
+/**
+ * Describes the structure of a number in the Luhn Algorithm.
+ */
+interface NumberInterface
+{
+    /**
+     * Get the number, without check digit.
+     *
+     * @return int
+     */
+    public function getNumber(): int;
+
+    /**
+     * Get the check digit for the number.
+     *
+     * @return int|null The check digit or null if it has not been calculated yet.
+     */
+    public function getCheckDigit(): ?int;
+}
\ No newline at end of file
diff --git a/src/LuhnAlgorithm.php b/src/LuhnAlgorithm.php
index f8dcd4a..68c0f86 100644
--- a/src/LuhnAlgorithm.php
+++ b/src/LuhnAlgorithm.php
@@ -26,6 +26,7 @@
 namespace Nekman\LuhnAlgorithm;
 
 use Nekman\LuhnAlgorithm\Contract\LuhnAlgorithmInterface;
+use Nekman\LuhnAlgorithm\Contract\NumberInterface;
 
 /**
  * {@inheritdoc}
@@ -34,32 +35,26 @@ class LuhnAlgorithm implements LuhnAlgorithmInterface {
 	/**
 	 * {@inheritDoc}
 	 */
-	public function isValid(string $number): bool {
-		// Remove everything except digits from the input.
-		$number = preg_replace("/[^\d]/", "", $number);
-		$nDigits = strlen($number);
-        $checkDigit = $number[$nDigits - 1];
-
-        // Remove the last digit of number.
-        $number = (int) $number;
-        $numberWithoutCheckDigit = (int) ($number / 10);
+	public function isValid(NumberInterface $number): bool {
+		if ($number->getCheckDigit() === null) {
+		    throw new \InvalidArgumentException("Check digit cannot be null.");
+        }
 
-        $checksum = $this->calcChecksum($numberWithoutCheckDigit);
-        $sum = $checksum + $checkDigit;
+        $checksum = $this->calcChecksum($number);
+		$sum = $checksum + $number->getCheckDigit();
 
-		// If the checksum  is divisible by 10 it is valid
+		// If the checksum is divisible by 10 it is valid.
 		return ($sum % 10) === 0;
 	}
 
 	/**
 	 * {@inheritDoc}
 	 */
-	public function calcCheckDigit(int $numberWithoutCheckDigit): int {
-		$checksum = (string) $this->calcChecksum($numberWithoutCheckDigit);
-		$nDigits = strlen($checksum);
+	public function calcCheckDigit(NumberInterface $number): int {
+		$checksum = $this->calcChecksum($number);
 		
 		// Get the last digit of the checksum.
-		$checkDigit = (int) $checksum[$nDigits - 1];
+		$checkDigit = $checksum % 10;
 
 		// If the check digit is not 0, then subtract the value from 10.
 		return $checkDigit === 0
@@ -70,14 +65,14 @@ public function calcCheckDigit(int $numberWithoutCheckDigit): int {
 	/**
 	 * {@inheritDoc}
 	 */
-	public function calcChecksum(int $numberWithoutCheckDigit): int {
-		$numberWithoutCheckDigit = (string) $numberWithoutCheckDigit;
-		$nDigits = strlen($numberWithoutCheckDigit);
+	public function calcChecksum(NumberInterface $number): int {
+		$number = (string) $number->getNumber();
+		$nDigits = strlen($number);
 		$checksum = 0;
 		$parity = $nDigits % 2;
 
 		for ($i = 0; $i < $nDigits; $i++) {
-		    $digit = (int) $numberWithoutCheckDigit[$i];
+		    $digit = (int) $number[$i];
 
 		    // Every other digit, starting from the leftmost,
             // shall be doubled.
diff --git a/src/Number.php b/src/Number.php
new file mode 100644
index 0000000..9efeaa6
--- /dev/null
+++ b/src/Number.php
@@ -0,0 +1,100 @@
+<?php
+
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Niklas Ekman
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+namespace Nekman\LuhnAlgorithm;
+
+use Nekman\LuhnAlgorithm\Contract\NumberInterface;
+
+/**
+ * Input for the Luhn Algorithm contains a number and a check digit.
+ */
+class Number implements NumberInterface
+{
+    /**
+     * @var int
+     */
+    private $number;
+
+    /**
+     * @var int|null
+     */
+    private $checkDigit;
+
+    /**
+     * Input constructor.
+     * @param int $number The number.
+     * @param int|null $checkDigit [Optional] The check digit for the number.
+     */
+    public function __construct(int $number, ?int $checkDigit = null)
+    {
+        $this->number = $number;
+        $this->checkDigit = $checkDigit;
+    }
+
+    /**
+     * Create a new number from an input that contains the check digit
+     * already.
+     *
+     * @param string $input The input that contains the check digit already.
+     *
+     * @return self
+     */
+    public static function fromString(string $input): self
+    {
+        $input = (int) preg_replace("/[^\d]/", "", $input);
+
+        // Get the last digit.
+        $checkDigit = $input % 10;
+
+        // Remove the last digit.
+        $number = (int) ($input / 10);
+
+        return new self($number, $checkDigit);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getNumber(): int
+    {
+        return $this->number;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getCheckDigit(): ?int
+    {
+        return $this->checkDigit;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function __toString()
+    {
+        return (string) $this->number . (string) $this->checkDigit;
+    }
+}
\ No newline at end of file
diff --git a/tests/LuhnAlgorithmTest.php b/tests/LuhnAlgorithmTest.php
index 21b2b84..aa40999 100644
--- a/tests/LuhnAlgorithmTest.php
+++ b/tests/LuhnAlgorithmTest.php
@@ -25,6 +25,7 @@
 
 namespace Nekman\LuhnAlgorithm\Test;
 
+use Nekman\LuhnAlgorithm\Number;
 use PHPUnit\Framework\TestCase;
 use Nekman\LuhnAlgorithm\LuhnAlgorithm;
 
@@ -49,10 +50,9 @@ public function testIsValid_success($number, $expected) {
 
 	public function provideIsValid_success() {
 		return [
-			["410321-9202", true],
-			[123455, true],
-			[4103219202, true],
-			[31997233700020, true],
+			[new Number(12345, 5), true],
+			[new Number(410321920, 2), true],
+			[new Number(3199723370002, 0), true],
 		];
 	}
 
@@ -65,7 +65,7 @@ public function testCalcChecksum_success($number, $expected) {
 
 	public function provideCalcChecksum_success() {
 		return [
-			[3199723370002, 50],
+			[new Number(3199723370002), 50],
 		];
 	}
 
@@ -78,9 +78,9 @@ public function testCalcCheckDigit_success($number, $expected) {
 
 	public function provideCalcCheckDigit_success() {
 		return [
-			[12345, 5],
-			[410321920, 2],
-			[3199723370002, 0],
+			[new Number(12345), 5],
+			[new Number(410321920), 2],
+			[new Number(3199723370002), 0],
 		];
 	}
 }
diff --git a/tests/NumberTest.php b/tests/NumberTest.php
new file mode 100644
index 0000000..cf2fe85
--- /dev/null
+++ b/tests/NumberTest.php
@@ -0,0 +1,48 @@
+<?php
+
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Niklas Ekman
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+namespace Nekman\LuhnAlgorithm\Test;
+
+use Nekman\LuhnAlgorithm\Number;
+use PHPUnit\Framework\TestCase;
+
+class NumberTest extends TestCase
+{
+    /**
+     * @dataProvider provideWithCheckDigit_success
+     */
+    public function testWithCheckDigit_success($number, $expected)
+    {
+        $this->assertEquals($expected, Number::fromString($number));
+    }
+
+    public function provideWithCheckDigit_success()
+    {
+        return [
+            ["410321-9202", new Number(410321920, 2)],
+            [4103219202, new Number(410321920, 2)]
+        ];
+    }
+}

From dd9c761ac3835a157f1498bca1db22965dad0747 Mon Sep 17 00:00:00 2001
From: Niklas Ekman <nikl.ekman@gmail.com>
Date: Mon, 26 Feb 2018 20:04:02 +0100
Subject: [PATCH 4/5] Code review changes.

---
 .gitignore                              |   1 +
 .php_cs.dist                            |  14 ++
 composer.json                           |   3 +-
 src/Contract/LuhnAlgorithmInterface.php | 125 +++++++--------
 src/Contract/NumberInterface.php        |  92 +++++------
 src/LuhnAlgorithm.php                   |  78 ++++-----
 src/LuhnAlgorithmFactory.php            |  96 ++++++------
 src/Number.php                          | 200 ++++++++++++------------
 tests/LuhnAlgorithmFactoryTest.php      |  74 ++++-----
 tests/LuhnAlgorithmTest.php             | 104 ++++++------
 tests/NumberTest.php                    |  96 ++++++------
 11 files changed, 458 insertions(+), 425 deletions(-)
 create mode 100644 .php_cs.dist

diff --git a/.gitignore b/.gitignore
index 7044502..e214b97 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 index.php
 nbproject/
 .idea/
+.php_cs.cache
 
 # Created by http://www.gitignore.io
 
diff --git a/.php_cs.dist b/.php_cs.dist
new file mode 100644
index 0000000..a70eec1
--- /dev/null
+++ b/.php_cs.dist
@@ -0,0 +1,14 @@
+<?php
+
+return PhpCsFixer\Config::create()
+    ->setRules([
+        '@PSR2' => true,
+        'ordered_imports' => true,
+        'phpdoc_order' => true,
+        'simplified_null_return' => false,
+        'no_unused_imports' => true,
+    ])->setFinder(
+        PhpCsFixer\Finder::create()
+            ->in(__DIR__.'/src')
+            ->in(__DIR__.'/tests')
+    );
diff --git a/composer.json b/composer.json
index 30db7b6..dc867e3 100644
--- a/composer.json
+++ b/composer.json
@@ -34,6 +34,7 @@
 		"php": "^7.1"
 	},
 	"require-dev": {
-		"phpunit/phpunit": "^6.5"
+		"phpunit/phpunit": "^6.5",
+		"friendsofphp/php-cs-fixer": "^2.10"
 	}
 }
diff --git a/src/Contract/LuhnAlgorithmInterface.php b/src/Contract/LuhnAlgorithmInterface.php
index 455604f..e80cacd 100644
--- a/src/Contract/LuhnAlgorithmInterface.php
+++ b/src/Contract/LuhnAlgorithmInterface.php
@@ -1,62 +1,63 @@
-<?php
-
-/*
- * The MIT License (MIT)
- *
- * Copyright (c) 2014 Niklas Ekman
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy of
- * this software and associated documentation files (the "Software"), to deal in
- * the Software without restriction, including without limitation the rights to
- * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
- * the Software, and to permit persons to whom the Software is furnished to do so,
- * subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all
- * copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
- * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
- * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
- * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
- * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- */
-
-namespace Nekman\LuhnAlgorithm\Contract;
-
-/**
- * Handles the Luhn Algorithm.
- * 
- * @link http://en.wikipedia.org/wiki/Luhn_algorithm 
- */
-interface LuhnAlgorithmInterface {
-    /**
-     * Determine if a number is valid according to the Luhn Algorithm.
-     *
-     * @param NumberInterface $number The number to validate.
-     *
-     * @return bool true if number is valid, false otherwise.
-     */
-    public function isValid(NumberInterface $number): bool;
-
-    /**
-     * Calculate the check digit for an input.
-     *
-     * @param NumberInterface $number The number, without check digit, to calculate the check digit for.
-     *
-     * @return int The check digit.
-     *
-     */
-    public function calcCheckDigit(NumberInterface $number): int;
-
-    /**
-     * Calulates the checksum for number.
-     *
-     * @param NumberInterface $number The number, without check digit, to calculate the checksum for.
-     *
-     * @return int The checksum.
-     *
-     */
-    public function calcChecksum(NumberInterface $number): int;
-}
+<?php
+
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Niklas Ekman
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+namespace Nekman\LuhnAlgorithm\Contract;
+
+/**
+ * Handles the Luhn Algorithm.
+ *
+ * @link http://en.wikipedia.org/wiki/Luhn_algorithm
+ */
+interface LuhnAlgorithmInterface
+{
+    /**
+     * Determine if a number is valid according to the Luhn Algorithm.
+     *
+     * @param NumberInterface $number The number to validate.
+     *
+     * @return bool true if number is valid, false otherwise.
+     */
+    public function isValid(NumberInterface $number): bool;
+
+    /**
+     * Calculate the check digit for an input.
+     *
+     * @param NumberInterface $number The number to calculate the check digit for.
+     *
+     * @return int The check digit.
+     *
+     */
+    public function calcCheckDigit(NumberInterface $number): int;
+
+    /**
+     * Calulates the checksum for number.
+     *
+     * @param NumberInterface $number The number to calculate the checksum for.
+     *
+     * @return int The checksum.
+     *
+     */
+    public function calcChecksum(NumberInterface $number): int;
+}
diff --git a/src/Contract/NumberInterface.php b/src/Contract/NumberInterface.php
index 210b65f..771b803 100644
--- a/src/Contract/NumberInterface.php
+++ b/src/Contract/NumberInterface.php
@@ -1,46 +1,46 @@
-<?php
-
-/*
- * The MIT License (MIT)
- *
- * Copyright (c) 2014 Niklas Ekman
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy of
- * this software and associated documentation files (the "Software"), to deal in
- * the Software without restriction, including without limitation the rights to
- * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
- * the Software, and to permit persons to whom the Software is furnished to do so,
- * subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all
- * copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
- * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
- * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
- * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
- * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- */
-
-namespace Nekman\LuhnAlgorithm\Contract;
-
-/**
- * Describes the structure of a number in the Luhn Algorithm.
- */
-interface NumberInterface
-{
-    /**
-     * Get the number, without check digit.
-     *
-     * @return int
-     */
-    public function getNumber(): int;
-
-    /**
-     * Get the check digit for the number.
-     *
-     * @return int|null The check digit or null if it has not been calculated yet.
-     */
-    public function getCheckDigit(): ?int;
-}
\ No newline at end of file
+<?php
+
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Niklas Ekman
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+namespace Nekman\LuhnAlgorithm\Contract;
+
+/**
+ * Describes the structure of a number in the Luhn Algorithm.
+ */
+interface NumberInterface
+{
+    /**
+     * Get the number, without check digit.
+     *
+     * @return int
+     */
+    public function getNumber(): int;
+
+    /**
+     * Get the check digit for the number.
+     *
+     * @return int|null The check digit or null if it has not been calculated yet.
+     */
+    public function getCheckDigit(): ?int;
+}
diff --git a/src/LuhnAlgorithm.php b/src/LuhnAlgorithm.php
index 68c0f86..5563245 100644
--- a/src/LuhnAlgorithm.php
+++ b/src/LuhnAlgorithm.php
@@ -31,53 +31,57 @@
 /**
  * {@inheritdoc}
  */
-class LuhnAlgorithm implements LuhnAlgorithmInterface {
-	/**
-	 * {@inheritDoc}
-	 */
-	public function isValid(NumberInterface $number): bool {
-		if ($number->getCheckDigit() === null) {
-		    throw new \InvalidArgumentException("Check digit cannot be null.");
+class LuhnAlgorithm implements LuhnAlgorithmInterface
+{
+    /**
+     * {@inheritDoc}
+     */
+    public function isValid(NumberInterface $number): bool
+    {
+        if ($number->getCheckDigit() === null) {
+            throw new \InvalidArgumentException("Check digit cannot be null.");
         }
 
         $checksum = $this->calcChecksum($number);
-		$sum = $checksum + $number->getCheckDigit();
+        $sum = $checksum + $number->getCheckDigit();
 
-		// If the checksum is divisible by 10 it is valid.
-		return ($sum % 10) === 0;
-	}
+        // If the checksum is divisible by 10 it is valid.
+        return ($sum % 10) === 0;
+    }
 
-	/**
-	 * {@inheritDoc}
-	 */
-	public function calcCheckDigit(NumberInterface $number): int {
-		$checksum = $this->calcChecksum($number);
-		
-		// Get the last digit of the checksum.
-		$checkDigit = $checksum % 10;
+    /**
+     * {@inheritDoc}
+     */
+    public function calcCheckDigit(NumberInterface $number): int
+    {
+        $checksum = $this->calcChecksum($number);
+        
+        // Get the last digit of the checksum.
+        $checkDigit = $checksum % 10;
 
-		// If the check digit is not 0, then subtract the value from 10.
-		return $checkDigit === 0
+        // If the check digit is not 0, then subtract the value from 10.
+        return $checkDigit === 0
             ? $checkDigit
             : 10 - $checkDigit;
-	}
+    }
 
-	/**
-	 * {@inheritDoc}
-	 */
-	public function calcChecksum(NumberInterface $number): int {
-		$number = (string) $number->getNumber();
-		$nDigits = strlen($number);
-		$checksum = 0;
-		$parity = $nDigits % 2;
+    /**
+     * {@inheritDoc}
+     */
+    public function calcChecksum(NumberInterface $number): int
+    {
+        $number = (string) $number->getNumber();
+        $nDigits = strlen($number);
+        $checksum = 0;
+        $parity = $nDigits % 2;
 
-		for ($i = 0; $i < $nDigits; $i++) {
-		    $digit = (int) $number[$i];
+        for ($i = 0; $i < $nDigits; $i++) {
+            $digit = (int) $number[$i];
 
-		    // Every other digit, starting from the leftmost,
+            // Every other digit, starting from the leftmost,
             // shall be doubled.
-		    if (($i % 2) !== $parity) {
-		        $digit *= 2;
+            if (($i % 2) !== $parity) {
+                $digit *= 2;
 
                 if ($digit > 9) {
                     $digit -= 9;
@@ -87,6 +91,6 @@ public function calcChecksum(NumberInterface $number): int {
             $checksum += $digit;
         }
 
-		return $checksum;
-	}
+        return $checksum;
+    }
 }
diff --git a/src/LuhnAlgorithmFactory.php b/src/LuhnAlgorithmFactory.php
index d08a4a1..6a95952 100644
--- a/src/LuhnAlgorithmFactory.php
+++ b/src/LuhnAlgorithmFactory.php
@@ -1,47 +1,49 @@
-<?php
-
-/*
- * The MIT License (MIT)
- *
- * Copyright (c) 2014 Niklas Ekman
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy of
- * this software and associated documentation files (the "Software"), to deal in
- * the Software without restriction, including without limitation the rights to
- * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
- * the Software, and to permit persons to whom the Software is furnished to do so,
- * subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all
- * copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
- * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
- * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
- * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
- * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- */
-
-namespace Nekman\LuhnAlgorithm;
-
-use Nekman\LuhnAlgorithm\Contract\LuhnAlgorithmInterface;
-
-/**
- * Factory for creating implementations of the Luhn Algorithm.
- */
-class LuhnAlgorithmFactory
-{
-    private function __construct() {
-        // Only static methods.
-    }
-
-    /**
-     * Create a new instance of an implementation of the Luhn Algorithm.
-     * 
-     * @return LuhnAlgorithmInterface Implementation of the Luhn Algorithm.
-     */
-    public static function create(): LuhnAlgorithmInterface {
-        return new LuhnAlgorithm();
-    }
-}
+<?php
+
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Niklas Ekman
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+namespace Nekman\LuhnAlgorithm;
+
+use Nekman\LuhnAlgorithm\Contract\LuhnAlgorithmInterface;
+
+/**
+ * Factory for creating implementations of the Luhn Algorithm.
+ */
+class LuhnAlgorithmFactory
+{
+    private function __construct()
+    {
+        // Only static methods.
+    }
+
+    /**
+     * Create a new instance of an implementation of the Luhn Algorithm.
+     *
+     * @return LuhnAlgorithmInterface Implementation of the Luhn Algorithm.
+     */
+    public static function create(): LuhnAlgorithmInterface
+    {
+        return new LuhnAlgorithm();
+    }
+}
diff --git a/src/Number.php b/src/Number.php
index 9efeaa6..822b9ef 100644
--- a/src/Number.php
+++ b/src/Number.php
@@ -1,100 +1,100 @@
-<?php
-
-/*
- * The MIT License (MIT)
- *
- * Copyright (c) 2014 Niklas Ekman
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy of
- * this software and associated documentation files (the "Software"), to deal in
- * the Software without restriction, including without limitation the rights to
- * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
- * the Software, and to permit persons to whom the Software is furnished to do so,
- * subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all
- * copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
- * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
- * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
- * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
- * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- */
-
-namespace Nekman\LuhnAlgorithm;
-
-use Nekman\LuhnAlgorithm\Contract\NumberInterface;
-
-/**
- * Input for the Luhn Algorithm contains a number and a check digit.
- */
-class Number implements NumberInterface
-{
-    /**
-     * @var int
-     */
-    private $number;
-
-    /**
-     * @var int|null
-     */
-    private $checkDigit;
-
-    /**
-     * Input constructor.
-     * @param int $number The number.
-     * @param int|null $checkDigit [Optional] The check digit for the number.
-     */
-    public function __construct(int $number, ?int $checkDigit = null)
-    {
-        $this->number = $number;
-        $this->checkDigit = $checkDigit;
-    }
-
-    /**
-     * Create a new number from an input that contains the check digit
-     * already.
-     *
-     * @param string $input The input that contains the check digit already.
-     *
-     * @return self
-     */
-    public static function fromString(string $input): self
-    {
-        $input = (int) preg_replace("/[^\d]/", "", $input);
-
-        // Get the last digit.
-        $checkDigit = $input % 10;
-
-        // Remove the last digit.
-        $number = (int) ($input / 10);
-
-        return new self($number, $checkDigit);
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function getNumber(): int
-    {
-        return $this->number;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function getCheckDigit(): ?int
-    {
-        return $this->checkDigit;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function __toString()
-    {
-        return (string) $this->number . (string) $this->checkDigit;
-    }
-}
\ No newline at end of file
+<?php
+
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Niklas Ekman
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+namespace Nekman\LuhnAlgorithm;
+
+use Nekman\LuhnAlgorithm\Contract\NumberInterface;
+
+/**
+ * Input for the Luhn Algorithm contains a number and a check digit.
+ */
+class Number implements NumberInterface
+{
+    /**
+     * @var int
+     */
+    private $number;
+
+    /**
+     * @var int|null
+     */
+    private $checkDigit;
+
+    /**
+     * Input constructor.
+     * @param int $number The number.
+     * @param int|null $checkDigit [Optional] The check digit for the number.
+     */
+    public function __construct(int $number, ?int $checkDigit = null)
+    {
+        $this->number = $number;
+        $this->checkDigit = $checkDigit;
+    }
+
+    /**
+     * Create a new number from an input that contains the check digit
+     * already.
+     *
+     * @param string $input The input that contains the check digit already.
+     *
+     * @return self
+     */
+    public static function fromString(string $input): self
+    {
+        $input = (int) preg_replace("/[^\d]/", "", $input);
+
+        // Get the last digit.
+        $checkDigit = $input % 10;
+
+        // Remove the last digit.
+        $number = (int) ($input / 10);
+
+        return new self($number, $checkDigit);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getNumber(): int
+    {
+        return $this->number;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getCheckDigit(): ?int
+    {
+        return $this->checkDigit;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function __toString()
+    {
+        return (string) $this->number . (string) $this->checkDigit;
+    }
+}
diff --git a/tests/LuhnAlgorithmFactoryTest.php b/tests/LuhnAlgorithmFactoryTest.php
index 865607a..f887f3e 100644
--- a/tests/LuhnAlgorithmFactoryTest.php
+++ b/tests/LuhnAlgorithmFactoryTest.php
@@ -1,36 +1,38 @@
-<?php
-
-/*
- * The MIT License (MIT)
- *
- * Copyright (c) 2014 Niklas Ekman
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy of
- * this software and associated documentation files (the "Software"), to deal in
- * the Software without restriction, including without limitation the rights to
- * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
- * the Software, and to permit persons to whom the Software is furnished to do so,
- * subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all
- * copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
- * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
- * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
- * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
- * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- */
-
-namespace Nekman\LuhnAlgorithm\Test;
-
-use PHPUnit\Framework\TestCase;
-use Nekman\LuhnAlgorithm\LuhnAlgorithm;
-use Nekman\LuhnAlgorithm\LuhnAlgorithmFactory;
-
-class LuhmAlgorithmFactoryTest extends TestCase {
-    public function testCreate() {
-        $this->assertInstanceOf(LuhnAlgorithm::class, LuhnAlgorithmFactory::create());
-    }
-}
+<?php
+
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Niklas Ekman
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+namespace Nekman\LuhnAlgorithm\Test;
+
+use Nekman\LuhnAlgorithm\LuhnAlgorithm;
+use Nekman\LuhnAlgorithm\LuhnAlgorithmFactory;
+use PHPUnit\Framework\TestCase;
+
+class LuhmAlgorithmFactoryTest extends TestCase
+{
+    public function testCreate()
+    {
+        $this->assertInstanceOf(LuhnAlgorithm::class, LuhnAlgorithmFactory::create());
+    }
+}
diff --git a/tests/LuhnAlgorithmTest.php b/tests/LuhnAlgorithmTest.php
index aa40999..de6a036 100644
--- a/tests/LuhnAlgorithmTest.php
+++ b/tests/LuhnAlgorithmTest.php
@@ -25,62 +25,70 @@
 
 namespace Nekman\LuhnAlgorithm\Test;
 
+use Nekman\LuhnAlgorithm\LuhnAlgorithm;
 use Nekman\LuhnAlgorithm\Number;
 use PHPUnit\Framework\TestCase;
-use Nekman\LuhnAlgorithm\LuhnAlgorithm;
 
-class LuhnAlgorithmTest extends TestCase {
-	/**
-	 * @var LuhnAlgorithm
-	 */
-	private $luhn;
+class LuhnAlgorithmTest extends TestCase
+{
+    /**
+     * @var LuhnAlgorithm
+     */
+    private $luhn;
 
-	public function setUp() {
-		parent::setUp();
-		
-		$this->luhn = new LuhnAlgorithm();
-	}
+    public function setUp()
+    {
+        parent::setUp();
+        
+        $this->luhn = new LuhnAlgorithm();
+    }
 
-	/**
-	 * @dataProvider provideIsValid_success
-	 */
-	public function testIsValid_success($number, $expected) {
-		$this->assertEquals($expected, $this->luhn->isValid($number));
-	}
+    /**
+     * @dataProvider provideIsValid_success
+     */
+    public function testIsValid_success($number, $expected)
+    {
+        $this->assertEquals($expected, $this->luhn->isValid($number));
+    }
 
-	public function provideIsValid_success() {
-		return [
-			[new Number(12345, 5), true],
-			[new Number(410321920, 2), true],
-			[new Number(3199723370002, 0), true],
-		];
-	}
+    public function provideIsValid_success()
+    {
+        return [
+            [new Number(12345, 5), true],
+            [new Number(410321920, 2), true],
+            [new Number(3199723370002, 0), true],
+        ];
+    }
 
-	/**
-	 * @dataProvider provideCalcChecksum_success
-	 */
-	public function testCalcChecksum_success($number, $expected) {
-		$this->assertEquals($expected, $this->luhn->calcChecksum($number));
-	}
+    /**
+     * @dataProvider provideCalcChecksum_success
+     */
+    public function testCalcChecksum_success($number, $expected)
+    {
+        $this->assertEquals($expected, $this->luhn->calcChecksum($number));
+    }
 
-	public function provideCalcChecksum_success() {
-		return [
-			[new Number(3199723370002), 50],
-		];
-	}
+    public function provideCalcChecksum_success()
+    {
+        return [
+            [new Number(3199723370002), 50],
+        ];
+    }
 
-	/**
-	 * @dataProvider provideCalcCheckDigit_success
-	 */
-	public function testCalcCheckDigit_success($number, $expected) {
-		$this->assertEquals($expected, $this->luhn->calcCheckDigit($number));
-	}
+    /**
+     * @dataProvider provideCalcCheckDigit_success
+     */
+    public function testCalcCheckDigit_success($number, $expected)
+    {
+        $this->assertEquals($expected, $this->luhn->calcCheckDigit($number));
+    }
 
-	public function provideCalcCheckDigit_success() {
-		return [
-			[new Number(12345), 5],
-			[new Number(410321920), 2],
-			[new Number(3199723370002), 0],
-		];
-	}
+    public function provideCalcCheckDigit_success()
+    {
+        return [
+            [new Number(12345), 5],
+            [new Number(410321920), 2],
+            [new Number(3199723370002), 0],
+        ];
+    }
 }
diff --git a/tests/NumberTest.php b/tests/NumberTest.php
index cf2fe85..a4a5754 100644
--- a/tests/NumberTest.php
+++ b/tests/NumberTest.php
@@ -1,48 +1,48 @@
-<?php
-
-/*
- * The MIT License (MIT)
- *
- * Copyright (c) 2014 Niklas Ekman
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy of
- * this software and associated documentation files (the "Software"), to deal in
- * the Software without restriction, including without limitation the rights to
- * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
- * the Software, and to permit persons to whom the Software is furnished to do so,
- * subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all
- * copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
- * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
- * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
- * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
- * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- */
-
-namespace Nekman\LuhnAlgorithm\Test;
-
-use Nekman\LuhnAlgorithm\Number;
-use PHPUnit\Framework\TestCase;
-
-class NumberTest extends TestCase
-{
-    /**
-     * @dataProvider provideWithCheckDigit_success
-     */
-    public function testWithCheckDigit_success($number, $expected)
-    {
-        $this->assertEquals($expected, Number::fromString($number));
-    }
-
-    public function provideWithCheckDigit_success()
-    {
-        return [
-            ["410321-9202", new Number(410321920, 2)],
-            [4103219202, new Number(410321920, 2)]
-        ];
-    }
-}
+<?php
+
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Niklas Ekman
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+namespace Nekman\LuhnAlgorithm\Test;
+
+use Nekman\LuhnAlgorithm\Number;
+use PHPUnit\Framework\TestCase;
+
+class NumberTest extends TestCase
+{
+    /**
+     * @dataProvider provideWithCheckDigit_success
+     */
+    public function testWithCheckDigit_success($number, $expected)
+    {
+        $this->assertEquals($expected, Number::fromString($number));
+    }
+
+    public function provideWithCheckDigit_success()
+    {
+        return [
+            ["410321-9202", new Number(410321920, 2)],
+            [4103219202, new Number(410321920, 2)]
+        ];
+    }
+}

From efd2a93a520fc1921ce28f1009c99fadb093d914 Mon Sep 17 00:00:00 2001
From: Niklas Ekman <nikl.ekman@gmail.com>
Date: Mon, 26 Feb 2018 20:08:38 +0100
Subject: [PATCH 5/5] Add test for number toString()

---
 tests/NumberTest.php | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tests/NumberTest.php b/tests/NumberTest.php
index a4a5754..443ab3f 100644
--- a/tests/NumberTest.php
+++ b/tests/NumberTest.php
@@ -45,4 +45,19 @@ public function provideWithCheckDigit_success()
             [4103219202, new Number(410321920, 2)]
         ];
     }
+
+    /**
+     * @dataProvider provideToString_success
+     */
+    public function testToString_success($number, $expected)
+    {
+        $this->assertEquals($expected, (string) $number);
+    }
+
+    public function provideToString_success()
+    {
+        return [
+            [new Number(12345, 5), "123455"]
+        ];
+    }
 }