R/loadDataFile.R

In MazamaCoreUtils: Utility Functions for Production R Code

#' @export
#'
#' @title Load data from URL or local file
#'
#' @param filename Name of the data file to be loaded.
#' @param dataUrl Remote URL directory for data files.
#' @param dataDir Local directory containing data files.
#' @return A data object.
#'
#' @description Loads pre-generated R binary files from a URL or a local
#' directory. This function is intended to be called by other \code{~_load()}
#' functions and can remove internet latencies when local versions of data are
#' available.
#'
#' For this reason, specification of \code{dataDir} always takes precedence over
#' \code{dataUrl}.

loadDataFile <- function(
  filename = NULL,
  dataUrl = NULL,
  dataDir = NULL
) {

  # ----- Validate parameters --------------------------------------------------

  MazamaCoreUtils::stopIfNull(filename)

  if ( is.null(dataUrl) && is.null(dataDir) ) {
    stop("either 'dataUrl' or 'dataDir' must be specified")
  }

  # ----- Load the data --------------------------------------------------------

  try({

    # Always check for dataDir first
    if (
      !is.null(dataDir) &&
      !is.na(dataDir) &&
      dir.exists(path.expand(dataDir))
    ) {

      # Load from a file
      filepath <- file.path(path.expand(dataDir), filename)

      result <- try({
        objectName <- load(filepath)
      }, silent = TRUE)

      if ( "try-error" %in% class(result) ) {
        stop(paste0("data file could not be loaded from: ", filepath))
      } else {
        loadedData <- get(objectName)
      }

    } else {

      # Load from a URL
      filepath <- paste0(dataUrl, '/', filename)

      # Define a 'connection' object so we can close it no matter what happens
      conn <- url(filepath)
      result <- try({
        objectName <- load(conn)
      }, silent = TRUE )
      close(conn)

      if ( "try-error" %in% class(result) ) {
        stop(paste0("data file could not be loaded from: ", filepath))
      } else {
        loadedData <- get(objectName)
      }

    }

  }, silent = TRUE) %>%
    stopOnError(paste0("data file could not be loaded from: ", filepath))

  # ----- Return ---------------------------------------------------------------

  return(loadedData)

}