added on_change_only argument to rotate_rds()

DESCRIPTION

@@ -1,7 +1,7 @@
 Type: Package
 Package: rotor
 Title: Log Rotation and Conditional Backups
-Version: 0.2.4.9002
+Version: 0.2.4.9003
 Authors@R: 
     person(given = "Stefan",
            family = "Fleck",

R/conditions.R

@@ -69,6 +69,30 @@ NotImplementedError <- function(
 
 
 
+ObjectHasNotChangedMessage <- function(message, ..., class = NULL, call = NULL){
+  condition(
+    message = as.character(message),
+      call = call,
+      class = union(class, c("ObjectHasNotChangedMessage", "message"))
+  )
+}
+
+
+
+
+condition <- function(message, ..., class = NULL, call = NULL){
+  structure(
+    list(
+      message = as.character(message),
+      call = call,
+      ...),
+    class = union(class, c("condition"))
+  )
+}
+
+
+
+
 error <- function(message, ..., class = NULL, call = NULL){
   structure(
     list(

R/rotate_rds.R

@@ -10,13 +10,16 @@
 #'   silently not rotate the file, while `rotate_rds_date()` will throw an
 #'   error.
 #'
+#' @param on_change_only `logical` scalar. Rotate only if `object` is different
+#'   from the object saved in `file`.
+#'
 #' @inheritParams base::saveRDS
 #' @inheritDotParams rotate
 #' @inheritParams  rotate_date
 #' @inheritDotParams rotate_date
 #' @inheritDotParams rotate_time
 #'
-#' @return `NULL` (invisibly)
+#' @return the path to `file` (invisibly)
 #' @export
 #'
 #' @examples
@@ -37,8 +40,24 @@ rotate_rds <- function(
   version = NULL,
   compress = TRUE,
   refhook = NULL,
-  ...
+  ...,
+  on_change_only = FALSE
 ){
+  assert(is_scalar_character(file))
+  assert(is_scalar_bool(on_change_only))
+
+  if (on_change_only && file.exists(file)){
+    comp <- readRDS(file)
+
+    if (
+      identical(object, comp) ||
+      (inherits(object, "data.table") && isTRUE(all.equal(object, comp)))
+    ){
+      message(ObjectHasNotChangedMessage("No change"))
+      return(invisible(file))
+    }
+  }
+
   if (file.exists(file))
     rotate(file, ...)
 
@@ -50,6 +69,7 @@ rotate_rds <- function(
     compress = compress,
     refhook = refhook
   )
+  invisible(file)
 }
 
 

tests/testthat/test_rotate_rds.R

@@ -50,3 +50,27 @@ test_that("rotate_rds_time works as expected", {
 
   expect_identical(n_backups(tf), 2L)
 })
+
+
+
+
+test_that("rotate_rds on_change_only", {
+  v <- LETTERS
+  df <- iris
+  dt <- data.table::as.data.table(iris)
+
+  td <- file.path(tempdir(), "rotate_rds_test_temp")
+  dir.create(td)
+  tf <- file.path(td, "testfile.rds")
+
+  on.exit(unlink(td, recursive = TRUE))
+
+  expect_silent(rotate_rds(v, tf, on_change_only = TRUE))
+  expect_message(rotate_rds(v, tf, on_change_only = TRUE), class = "ObjectHasNotChangedMessage")
+
+  expect_silent(rotate_rds(df, tf, on_change_only = TRUE))
+  expect_message(rotate_rds(df, tf, on_change_only = TRUE), class = "ObjectHasNotChangedMessage")
+
+  expect_silent(rotate_rds(dt, tf, on_change_only = TRUE))
+  expect_message(rotate_rds(dt, tf, on_change_only = TRUE), class = "ObjectHasNotChangedMessage")
+})