Vermietungs-Tool

A local web app for a small room-rental business in Austria: guest register,
room ledger, occupancy plan, invoices, the monthly tourist-tax report and the
quarterly VAT list. Application code only; it ships no data.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/vat.py

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+"""Quarterly Umsatzsteuer-Voranmeldung list, computed from the Zimmerbelegung.
+
+- A receipt belongs to the quarter it was PAID in (Ist-Besteuerung), not the one it was lived or invoiced
+  in. A row paid in several goes counts each payment on its own day; otherwise paid = the same rule the
+  Zimmerbelegung shows (`repo._payment`): the row's own date, else the date its invoice was paid.
+- Only the Betrag counts. The Ortstaxe is a durchlaufender Posten and never appears; payments cover the
+  Betrag first (175,00 paid of 175,00 Betrag + 16,00 Ortstaxe: the Betrag is in, the Ortstaxe open).
+- One Betrieb at a time — each unit files separately. A Betrieb includes its predecessors.
+- Everything is 10 % USt: Beherbergung, and the Garçonnières' residential rent alike. A Storno is nicht
+  steuerbar (`repo.is_storno`): listed, because the money came in, but kept out of the base.
+"""
+import datetime
+
+from app import db, repo
+
+VAT_RATE = 0.10
+
+
+def previous_quarter(today):
+    """The UVA is filed for the quarter that has just ended."""
+    q = (today.month - 1) // 3          # 0 = we are in the 1st quarter → last year's 4th
+    return (today.year, q) if q else (today.year - 1, 4)
+
+
+def _bounds(year, quarter):
+    first = datetime.date(year, 3 * quarter - 2, 1)
+    after = datetime.date(year + 1, 1, 1) if quarter == 4 else datetime.date(year, 3 * quarter + 1, 1)
+    return first.isoformat(), (after - datetime.timedelta(days=1)).isoformat()
+
+
+def receipts(row):
+    """When this row's money came in: [(date, part of the Betrag, part of the Ortstaxe)].
+
+    Recorded payments count one by one, each on its own day — an invoice paid half in May and half in
+    October belongs to two quarters. They cover the Betrag first and the Ortstaxe last. Without payments, a
+    paid row came in whole on its 'bezahlt am'."""
+    if row["payments"]:
+        out, left, taxe = [], row["amount"] or 0, row["tourism_tax"] or 0
+        for on, amount in row["payments"]:
+            part = round(min(amount, left), 2)
+            tax = round(min(amount - part, taxe), 2)
+            left, taxe = left - part, taxe - tax
+            if part > 0 or tax > 0:
+                out.append((on, part, tax))
+        return out
+    if row["payment"] in ("paid", "cash") and row["paid_on"]:
+        return [(row["paid_on"], row["amount"] or 0, row["tourism_tax"] or 0)]
+    return []
+
+
+def units(conn):
+    return db.rows(conn, "SELECT code, name FROM unit WHERE is_current=1 ORDER BY id")
+
+
+def quarterly_report(conn, unit_code, year, quarter):
+    first, last = _bounds(year, quarter)
+    codes = {r["code"] for r in db.rows(conn, "SELECT code FROM unit WHERE code=? OR succeeded_by_id="
+                                        "(SELECT id FROM unit WHERE code=?)", (unit_code, unit_code))}
+    rooms = {}
+    for r in repo.ledger_rows(conn):
+        if r["unit"] not in codes:
+            continue
+        for on, amount, _ in receipts(r):
+            if amount and first <= on <= last:
+                rooms.setdefault(r["room"] or "", []).append(
+                    dict(r, received_on=on, received=amount, storno=repo.is_storno(r)))
+    sections = [{"room": room, "rows": sorted(rows, key=lambda x: (x["received_on"], x["charge_id"])),
+                 "sum": round(sum(x["received"] for x in rows), 2)}
+                for room, rows in sorted(rooms.items())]
+    total = round(sum(s["sum"] for s in sections), 2)
+    storno = round(sum(x["received"] for s in sections for x in s["rows"] if x["storno"]), 2)
+    gross = round(total - storno, 2)
+    net = round(gross / (1 + VAT_RATE), 2)
+    return {"first": first, "last": last, "sections": sections, "total": total, "storno": storno,
+            "gross": gross, "net": net, "vat": round(gross - net, 2)}