Prevent OracleSummary transaction to be submitted twice (#99)

* Start timer only when there are not previous timer

* Start Oracle summary transaction only when there are no previous oracle summary transaction on the chain

lib/archethic/oracle_chain/scheduler.ex

@@ -33,10 +33,6 @@ defmodule ArchEthic.OracleChain.Scheduler do
     GenServer.start_link(__MODULE__, args, opts)
   end
 
-  def start_scheduling do
-    GenServer.cast(__MODULE__, :start_scheduling)
-  end
-
   def init(args) do
     polling_interval = Keyword.fetch!(args, :polling_interval)
     summary_interval = Keyword.fetch!(args, :summary_interval)
@@ -55,7 +51,8 @@ defmodule ArchEthic.OracleChain.Scheduler do
         state = %{polling_interval: polling_interval, summary_interval: summary_interval}
       ) do
     with ^first_public_key <- Crypto.first_node_public_key(),
-         nil <- Map.get(state, :polling_timer) do
+         nil <- Map.get(state, :polling_timer),
+         nil <- Map.get(state, :summary_timer) do
       polling_timer = schedule_new_polling(polling_interval)
       summary_timer = schedule_new_summary(summary_interval)
 
@@ -121,7 +118,14 @@ defmodule ArchEthic.OracleChain.Scheduler do
 
     date = DateTime.utc_now() |> DateTime.truncate(:second)
 
-    if trigger_node?(date) do
+    # Because the time to schedule the transaction can variate in milliseconds,
+    # a node could have stored an OracleSummary transaction but still
+    # receiving a message to create a new summary transaction.
+    # And this would be valid because the second didn't finished yet.
+    # So to prevent an new oracle summary, we are fetching the last transaction on the chain.
+    # If it's not a oracle_summary, then we can propose the summary transaction
+    with true <- last_transaction_not_summary?(date),
+         true <- trigger_node?(date) do
       Task.Supervisor.start_child(TaskSupervisor, fn ->
         handle_new_summary(date)
       end)
@@ -211,6 +215,21 @@ defmodule ArchEthic.OracleChain.Scheduler do
     |> TransactionChain.size()
   end
 
+  defp last_transaction_not_summary?(date = %DateTime{}) do
+    last_tx_address =
+      date
+      |> Crypto.derive_oracle_address(0)
+      |> TransactionChain.get_last_address()
+
+    case TransactionChain.get_transaction(last_tx_address, [:type]) do
+      {:ok, %Transaction{type: :oracle_summary}} ->
+        false
+
+      _ ->
+        true
+    end
+  end
+
   defp get_oracle_data(address) do
     case TransactionChain.get_transaction(address, data: [:content]) do
       {:ok, %Transaction{data: %TransactionData{content: previous_content}}} ->

mix.exs

@@ -4,7 +4,7 @@ defmodule ArchEthic.MixProject do
   def project do
     [
       app: :archethic,
-      version: "0.12.1",
+      version: "0.12.2",
       build_path: "_build",
       config_path: "config/config.exs",
       deps_path: "deps",