using mb_strtoupper and mb_strtolower normalize lower() and upper() method to handle advance use cases

Author: tamedevelopers

Str.php

@@ -902,7 +902,7 @@ public static function replace($search, $replace, $subject = null)
      */
     public static function lower($value = null)
     {
-        return strtolower(self::trim($value));
+        return self::normalize($value);
     }
 
     /**
@@ -913,7 +913,7 @@ public static function lower($value = null)
      */
     public static function upper($value = null)
     {
-        return strtoupper(self::trim($value));
+        return self::normalize($value, 'upper');
     }
 
     /**

Traits/StrTrait.php

@@ -167,6 +167,30 @@ public static function padString(string $value, int $length, string $padChar = '
         return str_pad($value, $length, $padChar, $padType);
     }
 
+    /**
+     * Normalize a string: trim and convert case.
+     *
+     * @param string|null $value
+     * @param string $case 'lower' or 'upper'
+     * @param string $encoding Optional, for multibyte support
+     * @return string
+     */
+    private static function normalize($value = null, string $case = 'lower', string $encoding = 'UTF-8'): string
+    {
+        $value = self::trim($value);
+
+        if ($case === 'upper') {
+            return function_exists('mb_strtoupper') 
+                ? mb_strtoupper(self::trim($value), $encoding) 
+                : strtoupper(self::trim($value));
+        }
+
+        // default: lower
+        return function_exists('mb_strtolower')
+            ? mb_strtolower(self::trim($value), $encoding) 
+            : strtolower(self::trim($value));
+    }
+
     /**
      * Replace Subject
      *