roffset.R

#' Create an offset rschedule
#'
#' @description
#' `roffset()` creates a new rschedule with events that are _offset_ from an
#' existing rschedule by a certain amount. This can be useful when generating
#' relative events like "the day after Christmas."
#'
#' @param rschedule `[rschedule]`
#'
#'   An rschedule to offset.
#'
#' @param by `[integer(1)]`
#'
#'   A single integer to offset by.
#'
#' @return
#' An offset rschedule.
#'
#' @export
#' @examples
#' on_christmas <- yearly() %>%
#'   recur_on_month_of_year("Dec") %>%
#'   recur_on_day_of_month(25)
#'
#' on_day_after_christmas <- roffset(on_christmas, by = 1)
#'
#' alma_search("2018-01-01", "2023-01-01", on_day_after_christmas)
#'
#' # Now what if you want the observed holiday representing the day after
#' # Christmas?
#' on_weekends <- weekly() %>% recur_on_weekends()
#'
#' # Adjust Christmas to the nearest weekday
#' on_christmas <- radjusted(on_christmas, on_weekends, adj_nearest)
#'
#' # Offset by 1 and then adjust that to the following weekday.
#' # We never adjust backwards because that can coincide with the observed day
#' # for Christmas.
#' on_day_after_christmas <- on_christmas %>%
#'   roffset(by = 1) %>%
#'   radjusted(on_weekends, adj_following)
#'
#' # Note that:
#' # - A Christmas on Friday the 24th resulted in a day after Christmas of
#' #   Monday the 27th
#' # - A Christmas on Monday the 26th resulted in a day after Christmas of
#' #   Tuesday the 27th
#' christmas <- alma_search("2018-01-01", "2023-01-01", on_christmas)
#' day_after_christmas <- alma_search("2018-01-01", "2023-01-01", on_day_after_christmas)
#'
#' lubridate::wday(christmas, label = TRUE)
#' lubridate::wday(day_after_christmas, label = TRUE)
roffset <- function(rschedule, by) {
  check_rschedule(rschedule)

  check_number_whole(by)
  by <- vec_cast(by, to = integer())

  new_roffset(rschedule, by)
}

new_roffset <- function(rschedule, by, ..., class = character()) {
  new_rschedule(
    rschedule = rschedule,
    by = by,
    ...,
    class = c(class, "almanac_roffset")
  )
}

#' @export
print.almanac_roffset <- function(x, ...) {
  by <- roffset_by(x)
  rschedule <- roffset_rschedule(x)

  cli::cli_text("<roffset[by = {by}]>")

  cli_indented()
  print(rschedule)
  cli::cli_end()

  invisible(x)
}

#' @export
rschedule_events.almanac_roffset <- function(x) {
  by <- roffset_by(x)
  rschedule <- roffset_rschedule(x)

  events <- rschedule_events(rschedule)
  events <- events + by

  events
}

roffset_rschedule <- function(x) {
  x$rschedule
}

roffset_by <- function(x) {
  x$by
}