do not allow update code

apps/block_scout_web/lib/block_scout_web/controllers/api/v1/decompiled_smart_contract_controller.ex

@@ -7,7 +7,8 @@ defmodule BlockScoutWeb.API.V1.DecompiledSmartContractController do
   def create(conn, params) do
     if auth_token(conn) == actual_token() do
       with {:ok, hash} <- validate_address_hash(params["address_hash"]),
-           :ok <- smart_contract_exists?(hash) do
+           :ok <- smart_contract_exists?(hash),
+           :ok <- decompiled_contract_exists?(params["address_hash"], params["decompiler_version"]) do
         case Chain.create_decompiled_smart_contract(params) do
           {:ok, decompiled_smart_contract} ->
             send_resp(conn, :created, Jason.encode!(decompiled_smart_contract))
@@ -22,8 +23,18 @@ defmodule BlockScoutWeb.API.V1.DecompiledSmartContractController do
             send_resp(conn, :unprocessable_entity, encode(errors))
         end
       else
-        :invalid_address -> send_resp(conn, :unprocessable_entity, encode(%{error: "address_hash is invalid"}))
+        :invalid_address ->
-        :not_found -> send_resp(conn, :unprocessable_entity, encode(%{error: "address is not found"}))
+          send_resp(conn, :unprocessable_entity, encode(%{error: "address_hash is invalid"}))
+
+        :not_found ->
+          send_resp(conn, :unprocessable_entity, encode(%{error: "address is not found"}))
+
+        :contract_exists ->
+          send_resp(
+            conn,
+            :unprocessable_entity,
+            encode(%{error: "decompiled code already exists for the decompiler version"})
+          )
       end
     else
       send_resp(conn, :forbidden, "")
@@ -44,6 +55,13 @@ defmodule BlockScoutWeb.API.V1.DecompiledSmartContractController do
     end
   end
 
+  defp decompiled_contract_exists?(address_hash, decompiler_version) do
+    case Chain.decompiled_code(address_hash, decompiler_version) do
+      {:ok, _} -> :contract_exists
+      _ -> :ok
+    end
+  end
+
   defp auth_token(conn) do
     case get_req_header(conn, "auth_token") do
       [token] -> token

apps/block_scout_web/test/block_scout_web/controllers/api/v1/decompiled_smart_contract_controller_test.exs

@@ -40,6 +40,30 @@ defmodule BlockScoutWeb.API.V1.DecompiledControllerTest do
       assert request.resp_body == "{\"decompiled_source_code\":\"can't be blank\"}"
     end
 
+    test "can not update code for the same decompiler version", %{conn: conn} do
+      address_hash = to_string(insert(:address, hash: "0x0000000000000000000000000000000000000001").hash)
+      decompiler_version = "test_decompiler"
+      decompiled_source_code = "hello world"
+
+      insert(:decompiled_smart_contract,
+        address_hash: address_hash,
+        decompiler_version: decompiler_version,
+        decompiled_source_code: decompiled_source_code
+      )
+
+      params = %{
+        "address_hash" => address_hash,
+        "decompiler_version" => decompiler_version,
+        "decompiled_source_code" => decompiled_source_code
+      }
+
+      request = post(conn, api_v1_decompiled_smart_contract_path(conn, :create), params)
+
+      assert request.status == 422
+
+      assert request.resp_body == "{\"error\":\"decompiled code already exists for the decompiler version\"}"
+    end
+
     test "creates decompiled smart contract", %{conn: conn} do
       address_hash = to_string(insert(:address, hash: "0x0000000000000000000000000000000000000001").hash)
       decompiler_version = "test_decompiler"

apps/explorer/lib/explorer/chain.ex

@@ -668,6 +668,20 @@ defmodule Explorer.Chain do
     end
   end
 
+  def decompiled_code(address_hash, version) do
+    query =
+      from(contract in DecompiledSmartContract,
+        where: contract.address_hash == ^address_hash and contract.decompiler_version == ^version
+      )
+
+    query
+    |> Repo.one()
+    |> case do
+      nil -> {:error, :not_found}
+      contract -> {:ok, contract.decompiled_source_code}
+    end
+  end
+
   @spec token_contract_address_from_token_name(String.t()) :: {:ok, Hash.Address.t()} | {:error, :not_found}
   def token_contract_address_from_token_name(name) when is_binary(name) do
     query =