1 files changed, 74 insertions, 0 deletions
diff --git a/shard/lib/data/signrev.ex b/shard/lib/data/signrev.ex
new file mode 100644
index 0000000..6360b53
--- /dev/null
+++ b/shard/lib/data/signrev.ex
@@ -0,0 +1,74 @@
+defmodule SData.SignRev do
+  @moduledoc"""
+  Implement a simple signed object with a revision number.
+  """
+
+
+  defstruct [:term, :rev, :signed]
+
+  @doc"""
+  New SignRev with an unsigned initial state (use this if initial state is deterministic/not signed).
+  """
+  def new(init_term) do
+    %__MODULE__{term: init_term, rev: 0, signed: nil}
+  end
+
+  @doc"""
+  New SignRev with a signed initial state.
+  """
+  def new(init_term, pk) do
+    bin = SData.term_bin {0, init_term}
+    case Shard.Keys.sign(pk, bin) do
+      {:ok, signed} ->
+        {:ok, %__MODULE__{term: init_term, rev: 0, signed: signed}}
+      err -> err
+    end
+  end
+
+  @doc"""
+  Get the current value of the SignRev.
+  """
+  def get(sr) do
+    sr.term
+  end
+
+  @doc"""
+  Update the SignRev with a new value and sign it with this pk
+  """
+  def set(sr, new_term, pk) do
+    rev = sr.rev + 1
+    bin = SData.term_bin {rev, new_term}
+    case Shard.Keys.sign(pk, bin) do
+      {:ok, signed} ->
+        {:ok, %__MODULE__{term: new_term, rev: rev, signed: signed}}
+      err -> err
+    end
+  end
+
+  @doc"""
+  Get the signed binary for the SignRev. Just send the output of this
+  to a peer for him to update.
+  """
+  def signed(sr) do
+    sr.signed
+  end
+
+  @doc"""
+  Check that a signed binary is correct and merge it into the SignRev.
+
+  Returns {true, new_sr} if an update happenned, {false, sr} otherwise.
+  """
+  def merge(sr, signed, pk) do
+    case Shard.Keys.open(pk, signed) do
+      {:ok, bin} ->
+        {rev, new_term} = SData.term_unbin bin
+        if rev > sr.rev do
+          {true, %__MODULE__{term: new_term, rev: rev, signed: signed}}
+        else
+          {false, sr}
+        end
+      _ ->
+        {false, sr}
+    end
+  end
+end