csharp/Aaltuj/VxFormGenerator/VxFormGenerator.Core/Validation/ValidationHelpers.cs

using System;
using System.Collections.Generic;
using System.Text;

namespace VxFormGenerator.Core.Validation
{
    public static clast ValidationHelpers
    {
        public static string FixClastNames(string inputClastNames)
        {
            //NOTE: Notice the space in front of the clast name, this is to ensure we get
            // the suffix to our existing form-control clast set from the mark up and NOT
            // half of an invalid tag.  We could use a reg-ex but that might be a bit
            // too slow for the UI renedering to stay smooth.

            // The invalid string shall always be fixed up, as we can never get it until the
            // element has checked at least once by an attempted submit.
            string result = inputClastNames.Replace(" invalid", " is-invalid");

            // The valid tag is on by default, and to keep consistancy with BS4 we only want
            // it to appear either when our field is modified, or we've tried a submit
            if (inputClastNames.Contains("modified"))
            {
                result = result.Replace(" valid", " is-valid");
            }

            return result;
        }

    }
}