Rename Type\IntegerValue to Type\Integer

Rename `Type\IntegerValue` to `Type\Integer`. It was originally named
`IntegerValue` because static analysis sees `Integer` in docblock
annotations and treats it as the native `int` type. `Integer` is not a
reserved word in PHP, so it should be named `Integer` for consistency
with other types in this library. When using it, a class alias prevents
static analysis from complaining.

src/Type/Integer.php

@@ -0,0 +1,89 @@
+<?php
+
+/**
+ * This file is part of the ramsey/uuid library
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @copyright Copyright (c) Ben Ramsey <ben@benramsey.com>
+ * @license http://opensource.org/licenses/MIT MIT
+ */
+
+declare(strict_types=1);
+
+namespace Ramsey\Uuid\Type;
+
+use Ramsey\Uuid\Exception\InvalidArgumentException;
+
+use function ctype_digit;
+use function ltrim;
+use function strpos;
+use function substr;
+
+/**
+ * A value object representing an integer
+ *
+ * This class exists for type-safety purposes, to ensure that integers
+ * returned from ramsey/uuid methods as strings are truly integers and not some
+ * other kind of string.
+ *
+ * To support large integers beyond PHP_INT_MAX and PHP_INT_MIN on both 64-bit
+ * and 32-bit systems, we store the integers as strings.
+ *
+ * @psalm-immutable
+ */
+final class Integer implements NumberInterface
+{
+    /**
+     * @var string
+     */
+    private $value;
+
+    /**
+     * @param mixed $value The integer value to store
+     */
+    public function __construct($value)
+    {
+        $value = (string) $value;
+        $sign = '+';
+
+        // If the value contains a sign, remove it for ctype_digit() check.
+        if (strpos($value, '-') === 0 || strpos($value, '+') === 0) {
+            $sign = substr($value, 0, 1);
+            $value = substr($value, 1);
+        }
+
+        if (!ctype_digit($value)) {
+            throw new InvalidArgumentException(
+                'Value must be a signed integer or a string containing only '
+                . 'digits 0-9 and, optionally, a sign (+ or -)'
+            );
+        }
+
+        // Trim any leading zeros.
+        $value = ltrim($value, '0');
+
+        // Set to zero if the string is empty after trimming zeros.
+        if ($value === '') {
+            $value = '0';
+        }
+
+        // Add the negative sign back to the value.
+        if ($sign === '-' && $value !== '0') {
+            $value = $sign . $value;
+        }
+
+        $this->value = $value;
+    }
+
+    public function toString(): string
+    {
+        return $this->value;
+    }
+
+    public function __toString(): string
+    {
+        return $this->toString();
+    }
+}