/// <summary>
    /// Defines operations related to validating cron expressions.
    /// </summary>
    public interface ICronValidator
    {
        /// <summary>
        /// Validates the given cron expression.
        /// </summary>
        /// <param name="cronExpression">The cron expression to validate.</param>
        /// <param name="errorMessage">An error message that will be set if the expression is invalid.</param>
        /// <returns>True if the cron expression is valid, otherwise false.</returns>
        bool ValidateCronExpression(string cronExpression, out string errorMessage);
    }

    /// <summary>
    /// A class that validates cron expressions using the cron expression API of Quartz.
    /// </summary>
    public class QuartzCronValidator : ICronValidator
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="QuartzCronValidator"/> class.
        /// </summary>
        public QuartzCronValidator()
        {
        }

        /// <summary>
        /// Validates the given cron expression.
        /// </summary>
        /// <param name="cronExpression">The cron expression to validate.</param>
        /// <param name="errorMessage">An error message that will be set if the expression is invalid.</param>
        /// <returns>True if the cron expression is valid, otherwise false.</returns>
        public bool ValidateCronExpression(string cronExpression, out string errorMessage)
        {
            // There doesn't appear to be any other way to do this with Quartz.NET.
            try
            {
                new CronExpression(cronExpression);
            }
            catch (FormatException ex)
            {
                errorMessage = ex.Message;
                return false;
            }

            errorMessage = null;
            return true;
        }
    }