.pick_cran <- function() {
  # Return a CRAN repo URL, preferring RSPM binaries if available for this OS
  rspm_template <- "https://packagemanager.rstudio.com/cran/__linux__/%s/latest"
  supported_os <- c("xenial", "bionic", "centos7", "opensuse42", "opensuse15")

  if (nzchar(Sys.which("lsb_release"))) {
    os <- tolower(system("lsb_release -cs", intern = TRUE))
    if (os %in% supported_os) {
      return(sprintf(rspm_template, os))
    }
  }
  if (file.exists("/etc/os-release")) {
    os_release <- readLines("/etc/os-release")
    vals <- sub("^.*=(.*)$", "\\1", os_release)
    os <- intersect(vals, supported_os)
    if (length(os)) {
      # e.g. "bionic"
      return(sprintf(rspm_template, os))
    } else {
      names(vals) <- sub("^(.*)=.*$", "\\1", os_release)
      if (vals["ID"] == "opensuse") {
        version <- sub('^"?([0-9]+).*"?.*$', "\\1", vals["VERSION_ID"])
        os <- paste0("opensuse", version)
        if (os %in% supported_os) {
          return(sprintf(rspm_template, os))
        }
      }
    }
  }
  if (file.exists("/etc/system-release")) {
    # Something like "CentOS Linux release 7.7.1908 (Core)"
    system_release <- tolower(utils::head(readLines("/etc/system-release"), 1))
    # Extract from that the distro and the major version number
    os <- sub("^([a-z]+) .* ([0-9]+).*$", "\\1\\2", system_release)
    if (os %in% supported_os) {
      return(sprintf(rspm_template, os))
    }
  }

  return("https://cloud.r-project.org")
}

options(
  Ncpus = parallel::detectCores(),
  repos = tryCatch(.pick_cran(), error = function(e) "https://cloud.r-project.org"),
  HTTPUserAgent = sprintf(
    'R/%s R (%s)',
    getRversion(),
    paste(getRversion(), R.version$platform, R.version$arch, R.version$os)
  )
)