ledger_entry: Support conditional expressions in amounts.

README.rst

@@ -42,7 +42,7 @@ Every setting in your configuration file has to be in a section.  ``[DEFAULT]``
 
 The first line of the template is a Ledger tag.  The program will leave all kinds of tags and Ledger comments alone, except to indent them nicely.
 
-The next two lines split the money across accounts.  They follow almost the same format as they do in Ledger: there's an account named, followed by a tab or two or more spaces, and then an expression.  Each time import2ledger generates an entry, it will evaluate this expression using the data it imported to calculate the actual currency amount to write.  Your expression can use numbers, basic arithmetic operators (including parentheses for grouping), and imported data referred to as ``{variable_name}``.
+The next two lines split the money across accounts.  They follow almost the same format as they do in Ledger: there's an account named, followed by a tab or two or more spaces, and then an expression.  Each time import2ledger generates an entry, it will evaluate this expression using the data it imported to calculate the actual currency amount to write.  Your expression can use numbers, basic arithmetic operators (including parentheses for grouping), conditional expressions in the format ``TRUE_EXPR if CONDITION else FALSE_EXPR``, and imported data referred to as ``{variable_name}``.
 
 import2ledger uses decimal math to calculate each amount, and rounds to the number of digits appropriate for that currency.  If the amount of currency being imported doesn't split evenly, spare change will be allocated to the last split to keep the entry balanced on both sides.
 

import2ledger/hooks/ledger_entry.py

@@ -54,7 +54,21 @@ class TokenTransformer:
 
 
 class AmountTokenTransformer(TokenTransformer):
-    SUPPORTED_OPS = frozenset('+-*/()')
+    SUPPORTED_NAMES = frozenset(['if', 'else'])
+    SUPPORTED_OPS = frozenset([
+        '(',
+        ')',
+        '+',
+        '-',
+        '*',
+        '/',
+        '==',
+        '!=',
+        '<',
+        '<=',
+        '>',
+        '>=',
+    ])
 
     def __iter__(self):
         tokens = super().__iter__()
@@ -66,6 +80,12 @@ class AmountTokenTransformer(TokenTransformer):
             raise ValueError("no amount in expression")
         yield from tokens
 
+    def transform_NAME(self, ttype, tvalue):
+        if tvalue in self.SUPPORTED_NAMES:
+            yield from self._noop_transformer(ttype, tvalue)
+        else:
+            raise ValueError("unsupported bare word {!r}".format(tvalue))
+
     def transform_NUMBER(self, ttype, tvalue):
         yield (tokenize.NAME, 'Decimal')
         yield (tokenize.OP, '(')

tests/data/templates.ini

@@ -47,6 +47,12 @@ template =
  Income:Sales  -{item_sales}
  ; :Item:
 
+[Conditional]
+template =
+ Assets:Cash  {amount} - (6 if {amount} > 50 else 3)
+ Expenses:Banking Fees  (6 if {amount} > 50 else 3)
+ Income:Sales  -{amount}
+
 [Empty]
 template =
 

tests/test_hook_ledger_entry.py

@@ -182,6 +182,23 @@ def test_line1_not_custom_payee():
         "  Income:Donations  -15.00 USD",
     ]
 
+@pytest.mark.parametrize('amount,expect_fee', [
+    (40, 3),
+    (80, 6),
+])
+def test_conditional(amount, expect_fee):
+    expect_cash = amount - expect_fee
+    amount_s = '{:.02f}'.format(amount)
+    render_vars = template_vars('Buyer', amount_s)
+    lines = render_lines(render_vars, 'Conditional')
+    assert lines == [
+        "",
+        "2015/03/14 Buyer",
+        "  Assets:Cash  {:.02f} USD".format(expect_cash),
+        "  Expenses:Banking Fees  {:.02f} USD".format(expect_fee),
+        "  Income:Sales  -{} USD".format(amount_s),
+    ]
+
 @pytest.mark.parametrize('amount_expr', [
     '',
     'name',