Add a generic caching function

.gitignore

@@ -1 +1 @@
-/input/cache.rds
+/cache

data.R

@@ -1,28 +1,5 @@
 library(data.table)
 
-#' Load and preprocess input data from `path`.
-#'
-#' A file named `cache.rds` will be created within that directory to reuse the
-#' results for future runs. To forcefully recompute, delete that file.
-#'
-#' @seealso [load_data()]
-load_data_cached <- function(path) {
-    cache_file <- paste(path, "cache.rds", sep = "/")
-
-    if (!file.exists(cache_file)) {
-        # If the cache file doesn't exist, we have to do the computation.
-        data <- load_data(path)
-
-        # The results are cached for the next run.
-        saveRDS(data, cache_file)
-
-        data
-    } else {
-        # If the cache file exists, we restore the data from it.
-        readRDS(cache_file)
-    }
-}
-
 #' Merge genome data from files in `path` into `data.table`s.
 #'
 #' The result will be a list with named elements:

server.R

@@ -4,8 +4,9 @@ library(shiny)
 
 source("data.R")
 source("scatter_plot.R")
+source("util.R")
 
-data <- load_data_cached("input")
+data <- run_cached("input", load_data, "input")
 
 server <- function(input, output) {
     output$genes <- renderDT({

util.R

@@ -0,0 +1,29 @@
+library(rlog)
+
+#' Run a function caching the result on the file system.
+#'
+#' The function will be called with the appended arguments. The [`id`] argument
+#' will be used to identify the cache file on the file system and in log
+#' messages.
+run_cached <- function(id, func, ...) {
+    if (!dir.exists("cache")) {
+        dir.create("cache")
+    }
+
+    cache_file <- paste("cache/", id, ".rds", sep = "")
+
+    if (file.exists(cache_file)) {
+        log_info(sprintf("Loading %s from cache", id))
+
+        # If the cache file exists, we restore the data from it.
+        readRDS(cache_file)
+    } else {
+        # If the cache file doesn't exist, we have to do the computation.
+        data <- func(...)
+
+        # The results are cached for the next run.
+        saveRDS(data, cache_file)
+
+        data
+    }
+}