Introduce Validator class

src/ParamResolver.php

@@ -137,14 +137,9 @@ private function resolveString(string $value, array $resolving = []): mixed
                 return $match[0];
             }
 
-            $resolved = $this->get($key);
-
-            if (!(is_numeric($resolved) || is_string($resolved))) {
-                throw new ParamResolverException("A string value must be composed of strings and/or numbers.");
-            }
+            $resolved = Validator::validateString($this->get($key));
 
             $resolving[$key] = true;
-            $resolved = (string)$resolved;
 
             return $this->resolveString($resolved, $resolving);
         }, $value);
@@ -195,11 +190,8 @@ private function unescapeValue(mixed $value): mixed
     private function get(int|string $propertyKey): mixed
     {
         $value = $this->findValue($propertyKey, $this->config);
-        if (!$value->valid()) {
-            throw new ParamResolverException("Parameter '$propertyKey' not found.");
-        }
 
-        return $value->current();
+        return Validator::validateGenerator($value, $propertyKey)->current();
     }
 
     /**
@@ -237,13 +229,7 @@ private function parseEnvironmentParams(string $value): ?string
         if (!str_starts_with($value, 'env.')) {
             return null;
         }
-        $env = substr($value, 4);
-        $envParam = getenv($env);
-
-        if ($envParam === false) {
-            throw new ParamResolverException("Environment variable '$env' is not defined.");
-        }
 
-        return $envParam;
+        return Validator::validateEnvParam(substr($value, 4));
     }
 }

src/Validator.php

@@ -0,0 +1,63 @@
+<?php declare(strict_types=1);
+/*
+ * Copyright (c) Cristiano Cinotti 2024.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+namespace Susina\ParamResolver;
+
+use Generator;
+use Susina\ParamResolver\Exception\ParamResolverException;
+
+/**
+ * Utility class to perform validations.
+ */
+class Validator
+{
+    /**
+     * Check if a value is only numeric or string.
+     */
+    public static function validateString(mixed $value): string
+    {
+        if (!(is_numeric($value) || is_string($value))) {
+            throw new ParamResolverException("A string value must be composed of strings and/or numbers.");
+        }
+
+        return (string) $value;
+    }
+
+    /**
+     * Check if a generator is correctly closed.
+     */
+    public static function validateGenerator(Generator $value, int|string $key): Generator
+    {
+        if (!$value->valid()) {
+            throw new ParamResolverException("Parameter '$key' not found.");
+        }
+
+        return $value;
+    }
+
+    /**
+     * Check if an environment variable exists.
+     */
+    public static function validateEnvParam(string $env): string
+    {
+        $envParam = getenv($env);
+
+        if ($envParam === false) {
+            throw new ParamResolverException("Environment variable '$env' is not defined.");
+        }
+
+        return $envParam;
+    }
+}