R/utils.R

In jsta/nadp: R package template to fetch and cache external data

cache_path <- function() paste0(rappdirs::user_data_dir(
                appname   = "nadp",
                appauthor = "nadp"), .Platform$file.sep)

get_if_not_exists <- function(url, destfile){
  if(!file.exists(destfile)){
    download.file(url, destfile)
  }else{
    message(paste0("A local copy of ", url, " already exists on disk"))
  }
}

stop_if_not_exists <- function(src_path) {
  if(!file.exists(src_path)){
    stop(paste0("Dataset not found at: ", src_path,
      "\n Try running the appropriate `get*` and/or `compile` commands."))
  }
}

get_version_list <- function(...){
  list.files(cache_path(), pattern = ".rds$", ...)
}

#' @importFrom curl new_handle parse_headers curl_fetch_memory
url_exists <- function(url){
  handle <- curl::new_handle(nobody = TRUE)

  tryCatch(
    length(curl::parse_headers(
      curl::curl_fetch_memory(url, handle)$headers)) > 0,
    error = function(e) FALSE
  )
}

product_string <- function(year, product){
  paste0("dep_", product, "_", year, ".tif")
}