Shuttle.Core.Cron

PM> Install-Package Shuttle.Core.Cron

Provides cron expression parsing:

 ┌───────────── minute (0 - 59)
 │ ┌───────────── hour (0 - 23)
 │ │ ┌───────────── day of the month (1 - 31)
 │ │ │ ┌───────────── month (1 - 12)
 │ │ │ │ ┌───────────── day of the week (1 - 7): Sunday to Saturday 
 │ │ │ │ │                                   
 │ │ │ │ │
 │ │ │ │ │
 * * * * *

This implementation starts from the minute field (so no second). Any seconds are removed from all dates that are used.

CronExpression

public CronExpression(string expression, ISpecificationFactory specificationFactory = null) : this(expression, DateTime.Now, specificationFactory);
public CronExpression(string expression, DateTime date, ISpecificationFactory specificationFactory = null);

Creates a CronExpression instance and parses the given expression. The date specifies to root date from which to determine either the next or previous occurrence.

public DateTime NextOccurrence();
public DateTime NextOccurrence(DateTime date);

Returns the next date that would follow the given date. This is accomplished by adding 1 muinute to the relevant date. If no date is provided the root date will be used. This method also sets the root date to the result.

public DateTime GetNextOccurrence(DateTime date);

Returns the next date that would follow the given date. If the given date satisfies the required specification(s) then the date is returned as-is.

public DateTime PreviousOccurrence();
public DateTime PreviousOccurrence(DateTime date);

Returns the previous date that would precede the given date. This is accomplished by subtracting 1 muinute from the relevant date. If no date is provided the root date will be used. This method also sets the root date to the result.

public DateTime GetPreviousOccurrence(DateTime date);

Returns the previous date that would precede the given date. If the given date satisfies the required specification(s) then the date is returned as-is.

Cron Samples

Format is {minute} {hour} {day-of-month} {month}

Field	Options
minutes	0-59 , - * /
hours	0-23 , - * /
day-of-month	1-31 , - * ? / L W
month	1-12 or JAN-DEC , - * /
day-of-week	1-7 or SUN-SAT , - * ? / L #

If day-of-month is specified then day-of-week should be ? and vice-versa.

Examples:

* * * * * - is every minute of every hour of every day of every month
5,10-12,17/5 * * * * - minute 5, 10, 11, 12, and every 5th minute after that

Specifications

Specifications need to implement ISpecification<CronField.Candidate>.

You may pass an implementation of the ISpecificationFactory as a parameter to the CronExpression. There is a DefaultSpecificationFactory that accepts a function callback in the constructor for scenarios where an explicit ISpecificationFactory implementation may not be warranted, e.g.:

var factory = new DefaultSpecificationFactory(parameters =>
{
    return !parameters.Expression.Equals("H", StringComparison.InvariantCultureIgnoreCase) 
        ? null 
        : new Specification<CronField.Candidate>(candidate => candidate.Date.Day % 2 == 0);
});