filters: Add audit_date() function.

conservancy_beancount/filters.py

@@ -14,6 +14,7 @@
 # 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 datetime
 import re
 
 from beancount.core import data as bc_data
@@ -39,6 +40,13 @@ from .beancount_types import (
 Postings = Iterable[data.Posting]
 Regexp = Union[str, Pattern]
 
+def audit_date(entries: Entries) -> Optional[datetime.date]:
+    for entry in entries:
+        if (isinstance(entry, bc_data.Custom)
+            and entry.type == 'conservancy_beancount_audit'):  # type:ignore[attr-defined]
+            return entry.date
+    return None
+
 def filter_meta_equal(postings: Postings, key: MetaKey, value: MetaValue) -> Postings:
     for post in postings:
         try:

tests/test_filters.py

@@ -22,6 +22,8 @@ from . import testutil
 
 from datetime import date
 
+from beancount.core import data as bc_data
+
 from conservancy_beancount import data
 from conservancy_beancount import filters
 
@@ -159,3 +161,25 @@ def test_remove_opening_balance_txn(opening_txn):
         for entry in entries
         for post in getattr(entry, 'postings', ())
     )
+
+@pytest.mark.parametrize('entry', [
+    bc_data.Custom({}, testutil.FY_START_DATE, 'conservancy_beancount_audit', []),
+    None,
+])
+def test_audit_date(entry):
+    dates = testutil.date_seq()
+    entries = [
+        bc_data.Open({}, next(dates), 'Income:Donations', ['USD'], None),
+        bc_data.Open({}, next(dates), 'Assets:Cash', ['USD'], None),
+        testutil.Transaction(postings=[
+            ('Income:Donations', -10),
+            ('Assets:Cash', 10),
+        ]),
+    ]
+    if entry is not None:
+        entries.append(entry)
+    actual = filters.audit_date(entries)
+    if entry is None:
+        assert actual is None
+    else:
+        assert actual == entry.date