feat(rules): add rule for CountryCode

app/Rules/CountryCodeExists.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Rules;
+
+use App\Models\Country;
+use Closure;
+use Illuminate\Contracts\Validation\ValidationRule;
+
+/**
+ * Determinate if given country code exists (only CZ for now, for example, add more countries as needed)
+ */
+class CountryCodeExists implements ValidationRule
+{
+    public function validate(string $attribute, mixed $value, Closure $fail): void
+    {
+        if (!in_array($value, ['CZ'])) {
+            $fail('validation.country_code_exists');
+        }
+
+        $country = Country::where('country_code', $value)->first();
+
+        if ($country === null) {
+            $fail('validation.country_code_exists_in_db');
+        }
+    }
+}