1 files changed, 49 insertions, 0 deletions
diff --git a/shard/lib/data/data.ex b/shard/lib/data/data.ex
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+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 """
+  Calculate the hash of an Erlang term by first converting it to its
+  binary representation.
+  """
+  def term_hash(term, algo \\ :sha256) 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