data: Add Posting.is_payment() method.

conservancy_beancount/data.py

@@ -20,6 +20,7 @@ throughout Conservancy tools.
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 import collections
+import decimal
 
 from beancount.core import account as bc_account
 
@@ -29,6 +30,7 @@ from typing import (
     MutableMapping,
     Optional,
     Sequence,
+    Union,
 )
 
 from .beancount_types import (
@@ -38,6 +40,8 @@ from .beancount_types import (
     Transaction,
 )
 
+DecimalCompat = Union[decimal.Decimal, int]
+
 LINK_METADATA = frozenset([
     'approval',
     'check',
@@ -207,6 +211,16 @@ class Posting(BasePosting):
     # If it did, this declaration would pass without issue.
     meta: Metadata  # type:ignore[assignment]
 
+    def is_payment(self, threshold: DecimalCompat=0) -> bool:
+        return (
+            self.account.is_real_asset()
+            and self.units.number is not None
+            # mypy says abs returns an object and we can't negate that.
+            # Since we know threshold is numeric, it seems safe to assume
+            # the return value of abs is numeric as well.
+            and self.units.number < -abs(threshold)  # type:ignore[operator]
+        )
+
 
 def iter_postings(txn: Transaction) -> Iterator[Posting]:
     """Yield an enhanced Posting object for every posting in the transaction"""

tests/test_data_posting.py

@@ -0,0 +1,94 @@
+"""Test Posting class"""
+# Copyright © 2020  Brett Smith
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+import pytest
+
+from . import testutil
+
+from decimal import Decimal
+
+import beancount.core.amount as bc_amount
+
+from conservancy_beancount import data
+
+PAYMENT_ACCOUNTS = {
+    'Assets:Cash',
+    'Assets:Checking',
+}
+
+NON_PAYMENT_ACCOUNTS = {
+    'Accrued:AccountsReceivable',
+    'Assets:PrepaidExpenses',
+    'Assets:PrepaidVacation',
+    'Expenses:Other',
+    'Income:Other',
+    'Liabilities:CreditCard',
+    'UnearnedIncome:MatchPledges',
+}
+
+def Posting(account, number,
+            currency='USD', cost=None, price=None, flag=None,
+            **meta):
+    if not meta:
+        meta = None
+    return data.Posting(
+        data.Account(account),
+        bc_amount.Amount(Decimal(number), currency),
+        cost,
+        price,
+        flag,
+        meta,
+    )
+
+def check_all_thresholds(post, threshold, expected):
+    assert post.is_payment(threshold) is expected
+    assert post.is_payment(-threshold) is expected
+    assert post.is_payment(Decimal(threshold)) is expected
+    assert post.is_payment(Decimal(-threshold)) is expected
+
+@pytest.mark.parametrize('acct', PAYMENT_ACCOUNTS)
+def test_is_payment(acct):
+    assert Posting(acct, -500).is_payment()
+
+@pytest.mark.parametrize('acct,amount,threshold', testutil.combine_values(
+    NON_PAYMENT_ACCOUNTS,
+    range(5, 20, 5),
+    range(0, 30, 10),
+))
+def test_is_not_payment_account(acct, amount, threshold):
+    post = Posting(acct, -amount)
+    assert not post.is_payment()
+    check_all_thresholds(post, threshold, False)
+
+@pytest.mark.parametrize('acct', PAYMENT_ACCOUNTS)
+def test_is_payment_with_threshold(acct):
+    threshold = len(acct) * 10
+    post = Posting(acct, -500)
+    check_all_thresholds(post, threshold, True)
+
+@pytest.mark.parametrize('acct', PAYMENT_ACCOUNTS)
+def test_is_not_payment_by_threshold(acct):
+    threshold = len(acct) * 10
+    post = Posting(acct, -9)
+    check_all_thresholds(post, threshold, False)
+
+@pytest.mark.parametrize('acct', PAYMENT_ACCOUNTS)
+def test_is_not_payment_but_credit(acct):
+    post = Posting(acct, 9)
+    assert not post.is_payment()
+    check_all_thresholds(post, 0, False)
+    check_all_thresholds(post, 5, False)
+    check_all_thresholds(post, 10, False)

tests/testutil.py

@@ -44,9 +44,15 @@ def check_post_meta(txn, *expected_meta, default=None):
             assert actual == expected
 
 def combine_values(*value_seqs):
+    stop = 0
+    for seq in value_seqs:
+        try:
+            stop = max(stop, len(seq))
+        except TypeError:
+            pass
     return itertools.islice(
         zip(*(itertools.cycle(seq) for seq in value_seqs)),
-        max(len(seq) for seq in value_seqs),
+        stop,
     )
 
 def parse_date(s, fmt='%Y-%m-%d'):