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Darecali

NuGet Samples Wiki

DATE RECURRENCE CALCULATION LIBRARY

Pronounced dah-rec-ah-lee

Produces sequences of dates using a specified recurrence strategy. Sequence controllers determine if and how a date sequence terminates.

Provides support for all recurrence strategies available in Microsoft Outlook, and then some.

Sequence control options

  • Non-terminating (infinite sequence; no end date)
  • Terminates at a specified date
  • Terminates after a specified number of occurrences
  • Terminates at either a specified date or after a number of occurrences (whichever comes first)

Recurrence strategies

  • Daily
  • Every {n} day(s)
  • Every weekday
  • Every weekend day
  • Weekly
  • Every day, every {n} week(s)
  • Every {n} week(s) on specified day(s)
  • Monthly
  • Every {n} month(s) on specified day(s)
  • Every {frequency} {day} of every {n} month(s)
  • Yearly
  • Every {n} year(s) on the specified day and month
  • Every {frequency} {day} of every specified month, every {n} years

Considerations for consumers

Start date influences first match

The start date affects the start of the period where recurrences are possible for the first match. This can result in a first match that may seem counter intuitive.

Example: "Recur the 1st day of every month" matches the start date for the first match, no matter what day of the month the start date is.

Strategies employ slippage

Strategies make no guarantee there will be a match in a particular period, which may seem counter intuitive.

Example: "Recur every month on the 30th day of the month" will never match in February.

Specifying a strategy

Use the Factory to create a SequenceController with either:

  • a concrete instance of an IRecurrenceStrategy, or
  • use the Strategy Definition Language to have one created for you.

The Factory can also create concrete instances of IRecurrenceStrategy using the Strategy Definition Language.

Call Factory.GetStrategyDefinitionUsage() to get the usage message, containing the syntax of the Strategy Definition Language:

Usage:
D[n]                     - Daily  : every n day(s)
                                    where n is an integer (default is 1)
Dwd                      - Daily  : every weekday
Dwe                      - Daily  : every weekend day
W[n]                     - Weekly : every day, every n week(s)
                                    where n is an integer (default is 1)
Wdays,n                  - Weekly : every n week(s) on specified day(s)
                                    where days are bitwise flags 1-127 (Sunday = 1)
                                          n is an integer
M[day[,n]]               - Monthly: every n month(s) on specified day
                                    where day is an integer 1-31 (default is 1)
                                          n is a positive integer (default is 1)
Mfrequency,day,n         - Monthly: every frequency day of every n month(s)
                                    where frequency is 1-4 for First-Fourth
                                                    or 'L' for Last
                                          day is 1-7 for Sunday-Saturday
                                              or 'd' for day
                                              or 'wd' for weekday
                                              or 'we' for weekend day
                                          n is a positive integer
Y[month[,day[,n]]]       - Yearly : every n year(s) on the specified day and month
                                    where month is 1-12 (default is 1)
                                          day is 1-31 (default is 1)
                                          n is a positive integer (default is 1)
Yfrequency,day,month,n   - Yearly : the frequency day of specified month, every n year(s)
                                    where frequency is 1-4 for First-Fourth
                                                    or 'L' for Last
                                          day is 1-7 for Sunday-Saturday
                                              or 'd' for day
                                              or 'wd' for weekday
                                              or 'we' for weekend day
                                          month is 1-12 for January-December
                                          n is a positive integer

NOTE: The usage message will also be part of an InvalidStrategyDefinitionException if the provided strategy definition is invalid.