first draft of a update_description_file() function cole-brokamp#12

DESCRIPTION

@@ -14,6 +14,7 @@ RoxygenNote: 6.1.1
 Depends:
     R (>= 3.1.0)
 Imports:
+    desc,
     dplyr,
     formatR,
     knitr,

NAMESPACE

@@ -8,5 +8,6 @@ export(install_deps_file)
 export(install_package_guess)
 export(make_deps_file)
 export(parse_packages)
+export(update_description_file)
 importFrom(magrittr,"%>%")
 importFrom(utils,packageDescription)

R/update_description_file.R

@@ -0,0 +1,30 @@
+#' add missing packages to package DESCRIPTION file
+#'
+#' @details uses \code{get_dependent_packages()} to find dependencies and
+#' adds them to the description file with the desc package
+#'
+#' @param directory folder to search for R and Rmd files.
+#' The DESCRIPTION file is expected to be in this directory.
+#'
+#' @export
+update_description_file <- function(directory = getwd()) {
+  description_file_path <- file.path(directory, "DESCRIPTION")
+  # check if a descripton file is available
+  if (!file.exists(description_file_path)) {
+    stop("There is no DESCRIPTION file in this directory.")
+  }
+  # get dependent packages
+  dependent_packages <- get_dependent_packages(directory)
+  # get description object
+  desc <- desc::description$new(description_file_path)
+  # add packages to description object
+  purrr::walk(
+    .x = dependent_packages,
+    .f = function(x, y) {
+      y$set_dep(x)
+    },
+    desc
+  )
+  # write description object to file system
+  desc$write(description_file_path)
+}