1 files changed, 38 insertions, 8 deletions

diff --git a/lib/ledger.ml b/lib/ledger.ml
index fd1b2a9..1d9a63c 100644
--- a/lib/ledger.ml
+++ b/lib/ledger.ml
@@ -98,13 +98,43 @@ module Account_id_key = struct
   type comparator_witness
 end
 
-type tx = {
-  cleared : Date.t option;
-  commodity_id : commodity_id;
-  debit : scalar Map.M(Account_id_key).t;
-  credit : scalar Map.M(Account_id_key).t;
-  labels : Labels.t;
-}
+module Tx : sig
+  type t
+  type error = Unbalanced
+
+  val make :
+    cleared:Date.t option ->
+    commodity_id:commodity_id ->
+    debit:scalar Map.M(Account_id_key).t ->
+    credit:scalar Map.M(Account_id_key).t ->
+    labels:Labels.t ->
+    (t, error) result
+
+  val cleared : t -> Date.t option
+  val commodity_id : t -> commodity_id
+  val debit : t -> scalar Map.M(Account_id_key).t
+  val credit : t -> scalar Map.M(Account_id_key).t
+  val labels : t -> Labels.t
+end = struct
+  (* We hide this because we only want to allow constructing balanced transactions *)
+  type t = {
+    cleared : Date.t option;
+    commodity_id : commodity_id;
+    debit : scalar Map.M(Account_id_key).t;
+    credit : scalar Map.M(Account_id_key).t;
+    labels : Labels.t;
+  }
+  [@@deriving fields]
+
+  type error = Unbalanced
+
+  (* TODO: check if debits and credits are balanced *)
+  let is_balanced _debits _credits = true
+
+  let make ~cleared ~commodity_id ~debit ~credit ~labels =
+    if not (is_balanced debit credit) then Error Unbalanced
+    else Ok { cleared; commodity_id; debit; credit; labels }
+end
 
-type item = Tx_item of tx | Bal_assert_item of bal_assert
+type item = Tx_item of Tx.t | Bal_assert_item of bal_assert
 type ledger = Ledger of item list