From 9d78e6e6472ecb0e5129056ea99d3f9cec432294 Mon Sep 17 00:00:00 2001
From: James Duncombe <james.duncombe@consilienceventures.com>
Date: Wed, 15 Nov 2023 17:11:34 +0000
Subject: [PATCH] Adds Signer behaviour.

---
 config/config.exs                              | 3 ++-
 lib/tt_eth.ex                                  | 4 ++++
 lib/tt_eth/behaviours/signer.ex                | 9 +++++++++
 lib/tt_eth/secp256k1.ex                        | 6 ++++++
 lib/tt_eth/transactions/eip1559_transaction.ex | 5 +++--
 5 files changed, 24 insertions(+), 3 deletions(-)
 create mode 100644 lib/tt_eth/behaviours/signer.ex

diff --git a/config/config.exs b/config/config.exs
index a7c9a72..57a2438 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -10,4 +10,5 @@ config :tt_eth,
     secondary: "0xe2187dc017e880dded10c403f7c0d397afb11736ac027c1202e318b0dd345086",
     ternary: "0xfa015243f2e6d8694ab037a7987dc73b1630fc8cb1ce82860344684c15d24026"
   ],
-  transaction_module: TTEth.Transactions.LegacyTransaction
+  transaction_module: TTEth.Transactions.LegacyTransaction,
+  signer_module: TTEth.Secp256k1
diff --git a/lib/tt_eth.ex b/lib/tt_eth.ex
index f3eece7..ccb87b8 100644
--- a/lib/tt_eth.ex
+++ b/lib/tt_eth.ex
@@ -123,6 +123,10 @@ defmodule TTEth do
   def transaction_module(),
     do: :tt_eth |> get_env(:transaction_module, TTEth.Transactions.EIP1559Transaction)
 
+  @spec signer_module() :: module
+  def signer_module(),
+    do: :tt_eth |> get_env(:signer_module, TTEth.Secp256k1)
+
   ## Mocks related stuff.
 
   @doc false
diff --git a/lib/tt_eth/behaviours/signer.ex b/lib/tt_eth/behaviours/signer.ex
new file mode 100644
index 0000000..2bc0dad
--- /dev/null
+++ b/lib/tt_eth/behaviours/signer.ex
@@ -0,0 +1,9 @@
+defmodule TTEth.Behaviours.Signer do
+  @moduledoc """
+  Defines a behaviour to encapsulate a signer.
+  """
+
+  @callback sign_transaction(transaction :: binary(), private_key :: binary()) ::
+              {:ok, {r_s :: binary(), v :: non_neg_integer()}}
+              | {:error, term()}
+end
diff --git a/lib/tt_eth/secp256k1.ex b/lib/tt_eth/secp256k1.ex
index 28b184c..5309fba 100644
--- a/lib/tt_eth/secp256k1.ex
+++ b/lib/tt_eth/secp256k1.ex
@@ -3,6 +3,12 @@ defmodule TTEth.Secp256k1 do
   Wrapper around `ExSecp256k1` functions.
   """
 
+  @behaviour TTEth.Behaviours.Signer
+
+  @impl TTEth.Behaviours.Signer
+  def sign_transaction(transaction, private_key),
+    do: ecdsa_sign_compact(transaction, private_key)
+
   @doc """
   Delegates to `ExSecp256k1.recover_compact/3` with guards around the `recovery_id` value.
   """
diff --git a/lib/tt_eth/transactions/eip1559_transaction.ex b/lib/tt_eth/transactions/eip1559_transaction.ex
index 9cf2243..6e3db14 100644
--- a/lib/tt_eth/transactions/eip1559_transaction.ex
+++ b/lib/tt_eth/transactions/eip1559_transaction.ex
@@ -4,9 +4,10 @@ defmodule TTEth.Transactions.EIP1559Transaction do
 
   SEE: https://eips.ethereum.org/EIPS/eip-1559
   """
-  alias TTEth.{BitHelper, Secp256k1}
+  alias TTEth.BitHelper
   alias TTEth.Behaviours.Transaction
   import BitHelper, only: [encode_unsigned: 1]
+  import TTEth, only: [signer_module: 0]
 
   @behaviour Transaction
 
@@ -89,7 +90,7 @@ defmodule TTEth.Transactions.EIP1559Transaction do
   Returns a ECDSA signature (v,r,s) for a given hashed value.
   """
   def sign_hash(hash, private_key) do
-    {:ok, {<<r::size(256), s::size(256)>>, v}} = Secp256k1.ecdsa_sign_compact(hash, private_key)
+    {:ok, {<<r::size(256), s::size(256)>>, v}} = signer_module().sign_compact(hash, private_key)
 
     {v, r, s}
   end