Quartz.CronExpression.GetTimeBefore

[Shariq]

I need Quartz.CronExpression.GetTimeBefore implementation. I am trying
to use it in an opensource project (it is in very early stages). What
is the expected time for this?

[shariq muhammad]

Actually because of the nature of Cron expression that it works in advancing chronological order, i think their is no solution, but using a brute force technique it is possible to do it with minimal code execution.

I have found an implementation in java here:

http://forums.terracotta.org/forums/posts/list/3099.page

So thought i share after converting it into C# so here it is:

public virtual DateTimeOffset? GetTimeBefore(DateTimeOffset beforeTimeUtc)

        {

            DateTimeOffset? nextFireTimeValid = GetTimeAfter(beforeTimeUtc);

            DateTimeOffset? nextFireTime = nextFireTimeValid;

            string[] expression = cronExpressionString.Split(' ');

            int incrementBy = 6;/*by default use years*/

            for (int j = 0; j < expression.Length; j++)

            {

                if (expression[j]=="*")

                {

                    incrementBy = j;

                    break;

                }

            }

            nextFireTime = nextFireTime.Value.AddSeconds(-1);

            switch (incrementBy)

            {

                case 0://[0]SEC

                    break;

                case 1://[1]MIN

                    nextFireTime = nextFireTime.Value.AddMinutes(-1);

                    break;

                case 2://[2]HOUR 

                    nextFireTime = nextFireTime.Value.AddHours(-1);

                    break;

                case 4://[4]MONTH

                    nextFireTime = nextFireTime.Value.AddMonths(-1);

                    break;

                case 3://[3]DAYOFMONTH

                case 5://[5]DAYOFWEEK

                    nextFireTime = nextFireTime.Value.AddYears(-1);

                    break;

                case 6://[6]YEAR

                default:

                    nextFireTime = nextFireTime.Value.AddYears(-1);

                    break;

            }

            DateTimeOffset? output  = GetTimeAfter(nextFireTime.Value);

            DateTimeOffset? tmp;

            bool searching = true;

            while (searching)

            {

                tmp = GetTimeAfter(output.Value);

                if (!tmp.HasValue)

                    return null;

                if (tmp.Value == nextFireTimeValid.Value)

                {

                    searching = false;

                }

                else

                {

                    output = GetTimeAfter(output.Value);

                }

            }

            return output;