Roman numeral converter

src/RomanNumeralsConverter.php

@@ -0,0 +1,50 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App;
+
+use Assert\Assert;
+
+final class RomanNumeralsConverter
+{
+    private static $map = [
+        1000 => 'M',
+        900 => 'CM',
+        500 => 'D',
+        400 => 'CD',
+        100 => 'C',
+        90 => 'XC',
+        50 => 'L',
+        40 => 'XL',
+        10 => 'X',
+        9 => 'IX',
+        5 => 'V',
+        4 => 'IV',
+        3 => 'III',
+        2 => 'II',
+        1 => 'I',
+    ];
+
+    public static function convert(int $input): string
+    {
+        Assert::that($input)
+            ->greaterOrEqualThan(0, 'Cannot convert negative numbers');
+
+        $letters = '';
+
+        while ($input > 0) {
+            foreach (static::$map as $number => $letter) {
+                if ($input >= $number) {
+                    // Add the appropriate numeral and reduce the value of
+                    // $input accordingly.
+                    $letters .= $letter;
+                    $input = ($input - $number);
+                    break;
+                }
+            }
+        }
+
+        return $letters;
+    }
+}