feat(validation): add type and size-based validation methods

Add string, array, min, max, between, and size validators to the
Validator class. A private measure helper centralizes size semantics
for numbers (value), strings (length), and arrays (element count).

src/Libs/Validator.php

@@ -228,6 +228,117 @@ class Validator
         return filter_var($subject, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE) !== null;
     }
 
+    /**
+     * Checks if the value is a string.
+     *
+     * Note this is the strict type check: a PHP integer (e.g. 42) or an array
+     * fails, while any string - including a numeric string like "42" - passes.
+     *
+     * @param mixed $subject The value to check.
+     *
+     * @return bool
+     */
+    public static function string(mixed $subject): bool
+    {
+        return is_string($subject);
+    }
+
+    /**
+     * Checks if the value is an array.
+     *
+     * @param mixed $subject The value to check.
+     *
+     * @return bool
+     */
+    public static function array(mixed $subject): bool
+    {
+        return is_array($subject);
+    }
+
+    /**
+     * Measures a value for the size-based rules (min/max/between/size).
+     *
+     * A numeric value is measured by its number, a plain string by its
+     * character length, and an array by its element count. This single helper
+     * keeps the size semantics consistent and is where the file case (kilobytes)
+     * is added later.
+     *
+     * @param mixed $subject The value to measure.
+     *
+     * @return float
+     */
+    private static function measure(mixed $subject): float
+    {
+        if (is_numeric($subject)) {
+            return (float) $subject;
+        }
+
+        if (is_string($subject)) {
+            return (float) (function_exists('mb_strlen') ? mb_strlen($subject) : strlen($subject));
+        }
+
+        if (is_array($subject)) {
+            return (float) count($subject);
+        }
+
+        return 0.0;
+    }
+
+    /**
+     * Checks if the measured value is greater than or equal to a minimum.
+     *
+     * @param mixed $subject The value to check.
+     * @param mixed $min     The minimum length, number or count.
+     *
+     * @return bool
+     */
+    public static function min(mixed $subject, mixed $min): bool
+    {
+        return static::measure($subject) >= (float) $min;
+    }
+
+    /**
+     * Checks if the measured value is less than or equal to a maximum.
+     *
+     * @param mixed $subject The value to check.
+     * @param mixed $max     The maximum length, number or count.
+     *
+     * @return bool
+     */
+    public static function max(mixed $subject, mixed $max): bool
+    {
+        return static::measure($subject) <= (float) $max;
+    }
+
+    /**
+     * Checks if the measured value is within an inclusive range.
+     *
+     * @param mixed $subject The value to check.
+     * @param mixed $min     The lower bound.
+     * @param mixed $max     The upper bound.
+     *
+     * @return bool
+     */
+    public static function between(mixed $subject, mixed $min, mixed $max): bool
+    {
+        $size = static::measure($subject);
+
+        return $size >= (float) $min && $size <= (float) $max;
+    }
+
+    /**
+     * Checks if the measured value is exactly a given size.
+     *
+     * @param mixed $subject The value to check.
+     * @param mixed $size    The expected length, number or count.
+     *
+     * @return bool
+     */
+    public static function size(mixed $subject, mixed $size): bool
+    {
+        return static::measure($subject) === (float) $size;
+    }
+
     /**
      * Checks if the value is a valid email address.
      *