Date validation

Sources/Validation/Validators/DateValidator.swift

@@ -0,0 +1,37 @@
+extension Validator where T == String {
+    /// Validates whether a `String` is a valid date.
+    ///
+    ///     try validations.add(\.createdAt, .date(formatter: dateFormatter))
+    ///
+    public static func date(_ dateFormatter: DateFormatter) -> Validator<T> {
+        return DateValidator(dateFormatter: dateFormatter).validator()
+    }
+}
+
+// MARK: Private
+
+/// Validates whether a string is a valid date.
+fileprivate struct DateValidator: ValidatorType {
+    /// See `ValidatorType`.
+    public var validatorReadable: String {
+        return "a valid date"
+    }
+
+    /// the DateFormatter used to validate the string
+    let dateFormatter: DateFormatter
+
+    /// Creates a new `DateValidator`.
+    public init(dateFormatter: DateFormatter) {
+        self.dateFormatter = dateFormatter
+    }
+
+    /// See `Validator`.
+    public func validate(_ s: String) throws {
+        guard
+            s.isEmpty ||
+            dateFormatter.date(from: s) != nil
+        else {
+            throw BasicValidationError("is not a valid date")
+        }
+    }
+}