R/oldest.R

In versionsort: Sort and Order Version Codes

#' Find the oldest version code
#'
#' @description `ver_oldest()` returns the oldest of the version codes.
#'
#' @inheritParams ver_order
#'
#' @return A character vector with one element.
#'
#' @examples
#' ver_oldest(c("1.3-0", "1.4-1", "0.0.0.9000", "1.4-0a", "1.4-0"))
#'
#' @seealso \code{\link{ver_latest}()}
#' @export
ver_oldest <- function(x) {
  if (length(x) == 0)
    stop("cannot select oldest version when given empty input")
  
  version_components <- strsplit(x, "[^\\w]+", perl = TRUE)
  ret <- Reduce(
    function(indices, position) {
      # Early return if the solution was found
      if (length(indices) == 1) return(indices)
      
      # Extract n-th components of version code
      # Empty components are extracted as NA (e.g. 4-th component of 1.5.0)
      nth_components <- vapply(
        version_components[indices], `[`, FUN.VALUE = character(1), position
      )
      
      # NA components take precedence over non-NA components
      if (any(is.na(nth_components))) {
        return(indices[which(is.na(nth_components))])
      }
      
      # Split components into initial numeric value and additional code
      # e.g. "0b8a" => 0 + "b8a"
      initial_number_match <- regexpr("^\\d+", nth_components)
      initial_number <- as.numeric(
        substring(nth_components, 1, attr(
          initial_number_match, "match.length", exact = TRUE)
        )
      )
      
      # Compare numeric values first
      if (any(!is.na(initial_number))) {
        # Codes are not empty, so initial_number is NA only when starting with a letter
        # That means NA initial numbers are later than anything else
        indices <- indices[which(initial_number == min(initial_number, na.rm = TRUE))]
        nth_components <- vapply(
          version_components[indices], `[`, FUN.VALUE = character(1), position
        )
        initial_number_match <- regexpr("^\\d+", nth_components)
      }
      
      # Compare codes only if necessary
      if (length(indices) > 1) {
        additional_code <- substring(nth_components, 1 + attr(
          initial_number_match, "match.length", exact = TRUE)
        )
        if (any(additional_code != "")) {
          indices <- indices[which(additional_code == min(additional_code))]
        }
      }
      indices
    },
    seq_len(max(lengths(version_components))),
    init = seq_along(version_components)
  )
  x[ret[1]]
}