gh_fill.R

#' Fill geohash prefix with members
#'
#' @param geohashes Character vector of input geohashes. They must all be of same precision
#' @param precision Positive integer scalar controlling the 'zoom level' – how many characters should be used in the output.
#' @return Character vector of geohashes corresponding to the input.
#' @export



gh_fill <- function(geohashes, precision) {
  if (uniqueN(nchar(geohashes)) > 1) {
    stop("Input Geohashes must all have the same precision level.")
  }
  if (sum(grepl("['ailo]", geohashes)) > 0) {
    stop("Invalid Geohash; Valid characters: [0123456789bcdefghjkmnpqrstuvwxyz]")
  }

  new_levels <- precision - nchar(geohashes[1])

  base32 <-
    unlist(strsplit("0123456789bcdefghjkmnpqrstuvwxyz", split = ""))

  grid <-
    do.call(data.table::CJ, append(list(geohashes), replicate(new_levels, base32, FALSE)))

  do.call(paste0, grid)

}