offline tool: add drain cmd

tools/offline_impl.ml

@@ -197,3 +197,33 @@ let wire_fee ~output ~master_key ~wire_method ~fee_start ~fee_end ~closing_fee
   let* s = Api.encode Api.WireFeeSetupMessage.jsont v in
   let* () = write_file output s in
   Ok ()
+
+let drain ~output ~master_key ~debit_account_section ~credit_payto_uri ~wtid
+    ~date ~amount =
+  let open Crypto in
+  let* key = read_master_key_file master_key in
+  let master_sig =
+    let open Bin_sig.MasterDrainProfit in
+    sign_f ~f:(EddsaSignature.sign ~key)
+      {
+        wtid;
+        date;
+        amount;
+        h_section= Bin_type.Hash_64_cstr.hash debit_account_section;
+        h_payto= Bin_type.FullPaytoHash.hash credit_payto_uri;
+      }
+  in
+  let v =
+    Api.DrainProfitsMessage.
+      {
+        debit_account_section;
+        credit_payto_uri;
+        wtid;
+        master_sig;
+        date;
+        amount;
+      }
+  in
+  let* s = Api.encode Api.DrainProfitsMessage.jsont v in
+  let* () = write_file output s in
+  Ok ()