R/where_is_gams.R

In christophe-gouel/gamsr: Tidy IO between GAMS and R

#' Find the location of GAMS
#'
#' Three strategies are tried in the following order:
#' 1. Find GAMS in the path.
#' 2. Find GAMS from the environment variable GAMSDIR.
#' 3. Find GAMS in the standard installation folder.
#' @return A 'character'.
#' @export
where_is_gams <- function() {
  sysname <- Sys.info()[["sysname"]]

  find_in_default_path <- function(sysname) {
    default_path <- c(
      Windows = "C:/GAMS",
      Linux = "/opt/gams",
      Darwin = "/Applications/GAMS"
    )
    default_path <- default_path[sysname]

    gams_path <- list.files(default_path)
    if (sysname == "Windows") gams_path <- as.integer(gams_path)
    gams_path <- sort(gams_path, decreasing = TRUE)[1]
    gams_path <- ifelse(is.na(gams_path), "",
      file.path(default_path, gams_path)
    )

    return(gams_path)
  }

  gams_path1 <- dirname(Sys.which("gams"))
  gams_path2 <- sub(";.*$", "", Sys.getenv("GAMSDIR"))
  gams_path3 <- find_in_default_path(sysname)
  if (length(gams_path1 != 0)) {
    return(gams_path1)
  } else if (length(gams_path2) != 0) {
    return(gams_path2)
  } else if (length(gams_path3) != 0) {
    return(gams_path3)
  } else {
    stop("Unable to find GAMS")
  }
}