transactions: fix paid fees still opened

The bit representation of real number
(https://en.wikipedia.org/wiki/IEEE_754) cause problem with arithmetic
operation on them (10-9.54 = 0.460000000000085). This commit fixes this
problem by multiplying transaction amount by 100 and cast them into
integer when arithmetic operations are done.

Closes rero#1373

Co-Authored-by: Renaud Michotte <renaud.michotte@gmail.com>

rero_ils/modules/patron_transaction_events/api.py

@@ -128,16 +128,25 @@ def create_event_from_patron_transaction(
 
     def update_parent_patron_transaction(self):
         """Update parent patron transaction amount and status."""
+        # NOTE :
+        #   due to bit representation of float number
+        #   (https://en.wikipedia.org/wiki/IEEE_754), the arithmetic operation
+        #   with float can cause some strange behavior
+        #     >>> 10 - 9.54
+        #     0.46000000000000085
+        #   To solve this problem in our case, as we keep only 2 decimal
+        #   digits, we can multiply amounts by 100, cast result as integer,
+        #   do operation with these values, and (at the end) divide the result
+        #   by 100.
         patron_transaction = self.patron_transaction()
-        total_amount = patron_transaction.get('total_amount')
+        total_amount = int(patron_transaction.get('total_amount') * 100)
         if self.event_type == 'fee':
-            total_amount = total_amount + self.amount
+            total_amount = total_amount + int(self.amount * 100)
         elif self.event_type in ('payment', 'cancel'):
-            total_amount = total_amount - self.amount
-        patron_transaction['total_amount'] = total_amount
+            total_amount = total_amount - int(self.amount * 100)
+        patron_transaction['total_amount'] = total_amount / 100
         if total_amount == 0:
             patron_transaction['status'] = 'closed'
-
         patron_transaction.update(
             patron_transaction, dbcommit=True, reindex=True)
 

tests/api/test_patron_payments_rest.py

@@ -46,7 +46,7 @@ def test_patron_payment(
     del payment['pid']
     payment['type'] = 'payment'
     payment['subtype'] = 'cash'
-    payment['amount'] = 1.00
+    payment['amount'] = 0.54
     payment['operator'] = {'$ref': get_ref_for_pid(
         'patrons', librarian_martigny_no_email.pid)}
     res, _ = postdata(
@@ -56,13 +56,13 @@ def test_patron_payment(
     )
     assert res.status_code == 201
     transaction = PatronTransaction.get_record_by_pid(transaction.pid)
-    assert transaction.total_amount == calculated_amount - 1.00
+    assert transaction.total_amount == 1.46
     assert transaction.status == 'open'
 
     # full payment
     payment['type'] = 'payment'
     payment['subtype'] = 'cash'
-    payment['amount'] = transaction.total_amount
+    payment['amount'] = 1.46
     res, _ = postdata(
         client,
         post_entrypoint,