cronexp ~master

cronexp

D framework providing parser of cron expressions and evaluator of next date and time of execution

About

Cron expression consists of 6 required fields separated by white space

Supported fields:

Field           Allowed values      Special charachters

Seconds         0-59                , - * /
Minutes         0-59                , - * /
Hours           0-23                , - * /
Day-of-month    1-31                , - * / ?
Month           1-12 or JAN-DEC     , - * /
Day-of-week     1-7 or MON-SUN      , - * / ?

Months names: JAN,FEB,MAR,APR,MAY,JUN,JUL,AUG,SEP,OCT,NOV,DEC
Days-of-week names: MON,TUE,WED,THU,FRI,SAT,SUN

Expression:

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

Charachters:

Asterisk (*) is used for specify all values (eg. 'every minute' in minute field)

Comma (,) is used for to separate items of a list (eg. using MON,WED,FRI in the 6th field (day of week) means Mondays, Wednesdays, Fridays)

Hyphen (-) is used for define ranges (eg. 10-30 in 1st field means every second between 10 and 30 inclusive)

Slash (/) is used for define step values, a/x = a, a+x, a+2x, a+3x, ... (eg. 2/4 in hours means list of 2,6,10,14,18,22)\ * in */x mean minimal allowed value (eg. 0 for hours, 1 for months etc)

Question mark (?) is a synonym of * for day-of-week and day-of-month fields used to explicitly indicate that days are set with other field

NOTES:

• If both the 'Day-of-month' and 'Day-of-week' fields are restricted (aren't *), next correct time will be when both fields match the conditions\ For example: * * * 13 * FRI expression will be satisfied only on friday 13th.
• Ranges can be overflowing, it means range NOV-FEB (NOV > FEB) will expand in NOV,DEC,JAN,FEB

Usage

import cron;

auto cron = CronExpr("30 * 12 1/2 NOV-FEB 2/2");
auto date = DateTime(2000, 6, 1, 10, 30, 0);
auto next = cron.getNext(date);

writeln(next); // 2000-Nov-07 12:00:30

Note that return type of CronExpr.getNext is Nullable!DateTime\ It can be Null if next date of execution is more than 4 years(1464 days)

For example:

import cron;

auto cron = CronExpr("0 0 0 29 FEB THU");
auto date = DateTime(2000, 1, 1, 0, 0, 0);
Nullable!DateTime next = cron.getNext(date);

assert(next.isNull); // Because next correct date in 2024 year