Amazon: Deduct pre-tax adjustments on new invoices

Newer style Amazon invoices only have the pre-tax adjustments
in the payments table but older invoices have them in the shipments
and payments tables (duplicated). This change handles both cases
and removes the "Expected, but actual" error when there are pre-tax
adjustments on the newer invoices

beancount_import/source/amazon_invoice.py

@@ -386,18 +386,24 @@ def parse_regular_order_invoice(path: str) -> Order:
     output_fields = dict()
     output_fields['pretax_adjustments'] = get_adjustments_in_table(
         payment_table, pretax_adjustment_fields_pattern)
-    amount = reduce_amounts(
-        a.amount for a in output_fields['pretax_adjustments'])
     payment_adjustments = collections.OrderedDict()  # type: Dict[str, Amount]
+
+    # older invoices put pre-tax amounts on a per-shipment basis
+    # new invoices only put pre-tax amounts on the overall payments section
+    # detect which this is
+    pretax_amount = reduce_amounts(
+        a.amount for a in output_fields['pretax_adjustments'])
+    shipments_pretax_amount = None
+
     if any(s.pretax_adjustments for s in shipments):
-        expected_amount = reduce_amounts(
-            a.amount
+        shipments_pretax_amount = reduce_amounts(a.amount
             for shipment in shipments
-            for a in shipment.pretax_adjustments)
-        if expected_amount != amount:
+            for a in shipment.pretax_adjustments)            
+
+        if shipments_pretax_amount != pretax_amount:
             errors.append(
                 'expected total pretax adjustment to be %s, but parsed total is %s'
-                % (expected_amount, amount))
+                % (expected_amount, pretax_amount))
 
     payments_total_adjustments = []
     shipments_total_adjustments = []
@@ -455,6 +461,12 @@ def resolve_posttax_adjustments():
 
     expected_total = add_amount(shipments_total_adjustment,
                                 reduce_amounts(x.total for x in shipments))
+
+    # if no shipments pre-tax section, then the expected total isn't accounting
+    # for the pre-tax adjustments yet since they are only in the grand total section
+    if shipments_pretax_amount is None:
+        expected_total = add_amount(expected_total, pretax_amount)
+
     adjusted_grand_total = add_amount(payments_total_adjustment, grand_total)
     if expected_total != adjusted_grand_total:
         errors.append('expected grand total is %s, but parsed value is %s' %