feat: Konto-Saldo-Anker mit ankerbasierter Saldenrechnung

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

finance/app/services/balances.py

@@ -1,26 +1,53 @@
+from datetime import date
 from decimal import Decimal
 
 from sqlalchemy import func, select
 from sqlalchemy.orm import Session
 
-from app.models.tables import Account, Statement, Transaction
+from app.models.tables import Account, Transaction
 
 
-def account_balance(session: Session, account: Account) -> Decimal:
-    stmt = session.execute(
-        select(Statement).where(Statement.account_id == account.id,
-                                Statement.status == "confirmed")
-        .order_by(Statement.period_end.desc())).scalars().first()
+def _confirmed_sum(session: Session, account_id: int,
+                   after: date | None, upto: date | None) -> Decimal:
+    """Summe bestaetigter Buchungen fuer `account_id` mit `after < booking_date
+    <= upto` (Raender werden nur gesetzt, wenn nicht None)."""
     q = select(func.coalesce(func.sum(Transaction.amount), 0)).where(
-        Transaction.account_id == account.id, Transaction.status == "confirmed")
-    if stmt is not None:
-        q = q.where(Transaction.booking_date > stmt.period_end)
-        base = stmt.closing_balance
-    else:
-        base = Decimal("0")
-    return Decimal(base) + Decimal(session.execute(q).scalar_one())
+        Transaction.account_id == account_id, Transaction.status == "confirmed")
+    if after is not None:
+        q = q.where(Transaction.booking_date > after)
+    if upto is not None:
+        q = q.where(Transaction.booking_date <= upto)
+    return Decimal(session.execute(q).scalar_one())
 
 
-def total_balance(session: Session) -> Decimal:
+def account_balance(session: Session, account: Account, at: date | None = None) -> Decimal:
+    """Kontostand am Ende des Tages `at` (Default: heute).
+
+    Konto-Saldo-Anker (Ausbaustufe 3 Task 1) ersetzt die bisherige
+    Statement-closing-Logik ersatzlos. Konvention: der Anker gilt PER
+    TAGESENDE des Ankerdatums - er enthaelt bereits alle Buchungen bis
+    einschliesslich diesem Tag.
+
+    Mit Anker: anchor_balance + Sum(tx: anchor_date < booking_date <= at)
+               - Sum(tx: at < booking_date <= anchor_date)
+    (jeweils nur eine der beiden Summen ist nicht-leer, je nachdem ob `at`
+    vor oder nach dem Anker liegt; bei at == anchor_date sind beide leer.)
+
+    Ohne Anker: Sum(tx: booking_date <= at) - bisheriges Verhalten mit Basis 0.
+    """
+    if at is None:
+        at = date.today()
+
+    if account.anchor_date is not None and account.anchor_balance is not None:
+        anchor_date = account.anchor_date
+        anchor_balance = Decimal(account.anchor_balance)
+        if at >= anchor_date:
+            return anchor_balance + _confirmed_sum(session, account.id, anchor_date, at)
+        return anchor_balance - _confirmed_sum(session, account.id, at, anchor_date)
+
+    return _confirmed_sum(session, account.id, None, at)
+
+
+def total_balance(session: Session, at: date | None = None) -> Decimal:
     accounts = session.execute(select(Account)).scalars().all()
-    return sum((account_balance(session, a) for a in accounts), Decimal("0"))
+    return sum((account_balance(session, a, at) for a in accounts), Decimal("0"))