R/recur-on-interval.R

In almanac: Tools for Working with Recurrence Rules

#' Recur on an interval
#'
#' `recur_on_interval()` adjusts the interval of the base frequency of the
#' recurrence rule. For example, a [monthly()] rule with an interval of 2 would
#' become "every other month".
#'
#' @param x `[rrule]`
#'
#'    A recurrence rule.
#'
#' @param n `[positive integer(1)]`
#'
#'    The interval on which to recur.
#'
#' @return
#' An updated rrule.
#'
#' @examples
#' # The default interval is 1
#' on_monthly <- monthly(since = "1999-01-01")
#'
#' alma_search("1999-01-01", "1999-06-01", on_monthly)
#'
#' # Adjust to every other month
#' on_every_other_month <- on_monthly %>% recur_on_interval(2)
#'
#' alma_search("1999-01-01", "1999-06-01", on_every_other_month)
#'
#' # Note that the frequency is limited to "every other month", but you
#' # can still have multiple events inside a single month
#' on_every_other_month_on_day_25_or_26 <- on_every_other_month %>%
#'   recur_on_day_of_month(25:26)
#'
#' alma_search("1999-01-01", "1999-06-01", on_every_other_month_on_day_25_or_26)
#'
#' @export
recur_on_interval <- function(x, n) {
  check_rrule(x)
  check_rule_not_set(x, "interval")

  check_number_whole(n, min = 1)
  n <- vec_cast(n, to = integer())

  tweak_rrule(x, interval = n)
}