"""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)}