added validators in project

BookHive/Validators/CustomValidators.cs

@@ -0,0 +1,28 @@
+using FluentValidation;
+
+namespace BookHive.Validators;
+
+public static class CustomValidators
+{
+    public static IRuleBuilderOptions<T, string>
+        IsValidIsbn13<T>(this IRuleBuilder<T, string> ruleBuilder)
+    {
+        return ruleBuilder
+            .Matches(@"^\d{13}$")
+            .WithMessage("L’ISBN doit contenir 13 chiffres.")
+            .Must(isbn =>
+            {
+                if (string.IsNullOrEmpty(isbn) || isbn.Length != 13)
+                    return false;
+                var sum = 0;
+                for (int i = 0; i < 12; i++)
+                {
+                    var digit = isbn[i] - '0';
+                    sum += (i % 2 == 0) ? digit : digit * 3;
+                }
+                var checkDigit = (10 - (sum % 10)) % 10;
+                return checkDigit == (isbn[12] - '0');
+            })
+            .WithMessage("Le chiffre de contrôle ISBN est invalide.");
+    }
+}