feat: Planungs- und Szenario-API mit Projektion und Vorschlaegen

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

finance/app/services/suggestions.py

@@ -0,0 +1,52 @@
+import statistics
+from collections import Counter, defaultdict
+from decimal import Decimal
+
+from sqlalchemy import select
+from sqlalchemy.orm import Session
+
+from app.models.tables import RecurringItem, Transaction
+
+
+def _max_consecutive_months(months: list[tuple[int, int]]) -> int:
+    if not months:
+        return 0
+    best = current = 1
+    for prev, cur in zip(months, months[1:]):
+        prev_idx = prev[0] * 12 + prev[1]
+        cur_idx = cur[0] * 12 + cur[1]
+        current = current + 1 if cur_idx == prev_idx + 1 else 1
+        best = max(best, current)
+    return best
+
+
+def suggest_recurring(session: Session) -> list[dict]:
+    txs = session.execute(
+        select(Transaction).where(Transaction.status == "confirmed")
+    ).scalars().all()
+    groups: dict[tuple, list[Transaction]] = defaultdict(list)
+    for t in txs:
+        groups[(t.account_id, t.counterparty, t.amount)].append(t)
+
+    existing = {(r.name, Decimal(r.amount))
+               for r in session.execute(select(RecurringItem)).scalars()}
+
+    suggestions: list[dict] = []
+    for (_account_id, counterparty, amount), items in groups.items():
+        months = sorted({(t.booking_date.year, t.booking_date.month) for t in items})
+        if _max_consecutive_months(months) < 3:
+            continue
+        name = counterparty
+        if (name, Decimal(amount)) in existing:
+            continue
+        due_day = int(statistics.median(sorted(t.booking_date.day for t in items)))
+        cat_counts = Counter(t.category_id for t in items if t.category_id is not None)
+        category_id = cat_counts.most_common(1)[0][0] if cat_counts else None
+        suggestions.append({
+            "name": name,
+            "amount": Decimal(amount),
+            "rhythm": "monthly",
+            "due_day": due_day,
+            "category_id": category_id,
+        })
+    return suggestions