From 4eaba1ebf645e43c383168e0fdde0ddf2ba9bc49 Mon Sep 17 00:00:00 2001
From: Brett Smith <brettcsmith@brettcsmith.org>
Date: Thu, 9 Apr 2020 15:11:16 -0400
Subject: [PATCH] data: Add is_opening_balance_txn function.

---
 conservancy_beancount/data.py             | 12 ++++-
 tests/test_data_is_opening_balance_txn.py | 59 +++++++++++++++++++++++
 tests/testutil.py                         | 18 +++++++
 3 files changed, 88 insertions(+), 1 deletion(-)
 create mode 100644 tests/test_data_is_opening_balance_txn.py

diff --git a/conservancy_beancount/data.py b/conservancy_beancount/data.py
index 7c016e0..2e0e217 100644
--- a/conservancy_beancount/data.py
+++ b/conservancy_beancount/data.py
@@ -21,7 +21,7 @@ throughout Conservancy tools.
 
 import collections
 import decimal
-import operator
+import functools
 
 from beancount.core import account as bc_account
 from beancount.core import amount as bc_amount
@@ -281,6 +281,16 @@ def balance_of(txn: Transaction,
         currency = weights[0].currency
     return Amount._make((number, currency))
 
+@functools.lru_cache()
+def is_opening_balance_txn(txn: Transaction) -> bool:
+    opening_equity = balance_of(txn, Account.is_opening_equity)
+    if not opening_equity.currency:
+        return False
+    rest = balance_of(txn, lambda acct: not acct.is_opening_equity())
+    if not rest.currency:
+        return False
+    return abs(opening_equity.number + rest.number) < decimal.Decimal('.01')
+
 def iter_postings(txn: Transaction) -> Iterator[Posting]:
     """Yield an enhanced Posting object for every posting in the transaction"""
     for index, source in enumerate(txn.postings):
diff --git a/tests/test_data_is_opening_balance_txn.py b/tests/test_data_is_opening_balance_txn.py
new file mode 100644
index 0000000..8d229d0
--- /dev/null
+++ b/tests/test_data_is_opening_balance_txn.py
@@ -0,0 +1,59 @@
+"""Test data.is_opening_balance_txn function"""
+# 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/>.
+
+from decimal import Decimal
+
+import pytest
+
+from . import testutil
+
+from conservancy_beancount import data
+
+def test_typical_opening():
+    txn = testutil.Transaction.opening_balance()
+    assert data.is_opening_balance_txn(txn)
+
+def test_multiacct_opening():
+    txn = testutil.Transaction(postings=[
+        ('Assets:Receivable:Accounts', 100),
+        (next(testutil.OPENING_EQUITY_ACCOUNTS), -100),
+        ('Liabilities:Payable:Accounts', -150),
+        (next(testutil.OPENING_EQUITY_ACCOUNTS), 150),
+    ])
+    assert data.is_opening_balance_txn(txn)
+
+def test_opening_with_fx():
+    txn = testutil.Transaction.opening_balance()
+    equity_post = txn.postings[-1]
+    txn.postings[-1] = equity_post._replace(
+        units=testutil.Amount(equity_post.units.number * Decimal('.9'), 'EUR'),
+        cost=testutil.Cost('1.11111'),
+    )
+    assert data.is_opening_balance_txn(txn)
+
+@pytest.mark.parametrize('acct1,acct2,number', [
+    ('Assets:Receivable:Accounts', 'Income:Donations', 100),
+    ('Expenses:Other', 'Liabilities:Payable:Accounts', 200),
+    ('Expenses:Other', 'Equity:Retained:Costs', 300),
+    # Release from restriction
+    ('Equity:Funds:Unrestricted', 'Equity:Funds:Restricted', 400),
+])
+def test_not_opening_balance(acct1, acct2, number):
+    txn = testutil.Transaction(postings=[
+        (acct1, number),
+        (acct2, -number),
+    ])
+    assert not data.is_opening_balance_txn(txn)
diff --git a/tests/testutil.py b/tests/testutil.py
index c1b4580..87e68fc 100644
--- a/tests/testutil.py
+++ b/tests/testutil.py
@@ -107,6 +107,12 @@ NON_STRING_METADATA_VALUES = [
     Amount(500, None),
 ]
 
+OPENING_EQUITY_ACCOUNTS = itertools.cycle([
+    'Equity:Funds:Unrestricted',
+    'Equity:Funds:Restricted',
+    'Equity:OpeningBalance',
+])
+
 class Transaction:
     def __init__(self,
                  date=FY_MID_DATE, flag='*', payee=None,
@@ -147,6 +153,18 @@ class Transaction:
             posting = arg
         self.postings.append(posting)
 
+    @classmethod
+    def opening_balance(cls, acct=None, **txn_meta):
+        if acct is None:
+            acct = next(OPENING_EQUITY_ACCOUNTS)
+        return cls(**txn_meta, postings=[
+            ('Assets:Receivable:Accounts', 100),
+            ('Assets:Receivable:Loans', 200),
+            ('Liabilities:Payable:Accounts', -15),
+            ('Liabilities:Payable:Vacation', -25),
+            (acct, -260),
+        ])
+
 
 class TestConfig:
     def __init__(self, *,