Add nwe DataAnnotation DatetimeNotInThePast

Retroactiune.WebAPI/DataAnnotations/DatetimeNotInThePast.cs

@@ -0,0 +1,22 @@
+using System;
+using System.ComponentModel.DataAnnotations;
+
+namespace Retroactiune.DataAnnotations
+{
+    public class DatetimeNotInThePast : ValidationAttribute
+    {
+
+        /// <summary>
+        /// Validates the given DateTime object to be null or greater than the UtcNow date.
+        /// </summary>
+        /// <param name="value">An DateTime object.</param>
+        /// <returns>True if the date is null or in the future, false otherwise.</returns>
+        public override bool IsValid(object value)
+        {
+            // TODO: Test
+            var now = DateTime.UtcNow;
+            var date = value as DateTime?;
+            return !(date <= now);
+        }
+    }
+}