Add persistency to playlog.

Refs #333.

libs/utils.liq

@@ -48,22 +48,37 @@ end
 # was last played and avoid repetitions.
 # @param ~duration Duration (in seconds) after which songs are forgotten. By default, songs are not forgotten which means that the playlog will contain all the songs ever played.
 # @param ~hash Function to extract an identifier from the metadata. By default, the filename is used but we could return the artist to know when a song from a given artist was last played for instance.
+# @param ~persistency Set a file name where the values are stored and loaded in case the script is restarted.
 # @category Source / Track Processing
 # @method add Record that file with given metadata has been played.
 # @method last How long ago a file was played (in seconds), `infinity` is returned if the song has never been played.
-def playlog(~duration=infinity, ~hash=fun(m)->m["filename"])
+def playlog(~duration=infinity, ~persistency=null(), ~hash=fun(m)->m["filename"])
   l = ref([])
+  # Load from persistency file
+  if null.defined(persistency) then
+    l := of_json(default=[("", 0.)], file.contents(null.get(persistency)))
+  end
+  # Save into persistency file
+  def save()
+    if null.defined(persistency) then
+      file.write(data=json_of(!l), null.get(persistency))
+    end
+  end
+  # Remove too old elements
   def prune()
     if duration != infinity then
       t = time()
       l := list.assoc.filter(fun(f, tf) -> t - tf <= duration, !l)
     end
   end
+  # Add a new entry
   def add(m)
     prune()
     f = hash(m)
     l := list.add((f, time()), !l)
+    save()
   end
+  # Last time this entry was played
   def last(m)
     f = hash(m)
     time() - list.assoc(default = 0.-infinity, f, !l)