1 files changed, 35 insertions, 0 deletions
diff --git a/lib/data/data.ex b/lib/data/data.ex
index 428957c..c2c659d 100644
--- a/lib/data/data.ex
+++ b/lib/data/data.ex
@@ -1,6 +1,13 @@
 defmodule SData do
   @moduledoc """
   Utility functions
+
+  Compare functions are functions that compares stored items and provides a total order.
+  They must return:
+    - `:after` if the first argument is more recent
+    - `:duplicate` if the two items are the same
+    - `:before` if the first argument is older
+  These functions must only return :duplicate for equal items.
   """
 
   @doc """
@@ -11,4 +18,32 @@ defmodule SData do
     :crypto.hash(algo, (:erlang.term_to_binary term))
   end
 
+  @doc"""
+    Compare function for arbitrary terms using the Erlang order
+  """
+  def cmp_term(a, b) do
+    cond do
+      a > b -> :after
+      a < b -> :before
+      a == b -> :duplicate
+    end
+  end
+
+  @doc"""
+    Compare function for timestamped strings
+  """
+  def cmp_ts_str({ts1, str1}, {ts2, str2}) do
+    cond do
+      ts1 > ts2 -> :after
+      ts1 < ts2 -> :before
+      str1 > str2 -> :after
+      str1 < str2 -> :before
+      true -> :duplicate
+    end
+  end
+
+  @doc"""
+    Merge function for nils
+  """
+  def merge_true(true, true), do: true
 end