certain/backend/app/routers/transactions.py

"""Transaktionen: Ausgabe, Einnahme, interner Transfer. Owner-gescoped.

Beim Speichern wird der eingefrorene EUR-Wert (``amount_eur_cents``) zum
Buchungsdatum berechnet (Pivot für Budget/Dashboard). Ein manuell gesetzter
Kurs (``fx_rate``) hat Vorrang vor dem EZB-Kurs.
"""

from datetime import date

from fastapi import APIRouter, Depends, HTTPException, Query, status
from sqlalchemy.orm import Session

from ..database import get_db
from ..deps import get_current_user, get_owned
from ..models import Account, Category, Transaction, TxnType, User
from ..schemas import TransactionCreate, TransactionOut, TransactionUpdate
from ..services import currency
from .accounts import base_currency

router = APIRouter(prefix="/transactions", tags=["transactions"])


def _fx(txn: Transaction) -> float | None:
    return float(txn.fx_rate) if txn.fx_rate is not None else None


def _recompute(db: Session, txn: Transaction, from_acc: Account, to_acc: Account | None) -> None:
    """Setzt amount_eur_cents und (bei Transfers) to_amount_cents neu."""
    txn.amount_eur_cents = currency.compute_amount_eur_cents(
        db, txn.amount_cents, from_acc.currency, txn.date, _fx(txn)
    )
    if txn.type == TxnType.transfer and to_acc is not None:
        if txn.to_amount_cents is None:
            if to_acc.currency == from_acc.currency:
                txn.to_amount_cents = txn.amount_cents
            else:
                conv = currency.convert(
                    db, txn.amount_cents, from_acc.currency, to_acc.currency, txn.date, _fx(txn)
                )
                txn.to_amount_cents = conv if conv is not None else txn.amount_cents
    else:
        txn.to_amount_cents = None


def to_out(db: Session, txn: Transaction, base: str, ccy_by_account: dict[int, str]) -> TransactionOut:
    acc_ccy = ccy_by_account.get(txn.account_id, "EUR")
    if base == "EUR":
        amount_base = txn.amount_eur_cents
    else:
        conv = currency.from_eur_cents(db, txn.amount_eur_cents, base, txn.date)
        amount_base = conv if conv is not None else txn.amount_eur_cents
    return TransactionOut(
        id=txn.id,
        type=txn.type,
        date=txn.date,
        time=txn.time,
        account_id=txn.account_id,
        to_account_id=txn.to_account_id,
        account_currency=acc_ccy,
        amount_cents=txn.amount_cents,
        to_amount_cents=txn.to_amount_cents,
        fx_rate=_fx(txn),
        amount_eur_cents=txn.amount_eur_cents,
        amount_base_cents=amount_base,
        category_id=txn.category_id,
        budget_treatment=txn.budget_treatment,
        budget_category_id=txn.budget_category_id,
        payee=txn.payee,
        description=txn.description,
        notes=txn.notes,
    )


def _currency_map(db: Session, user: User) -> dict[int, str]:
    rows = db.query(Account.id, Account.currency).filter(Account.owner_id == user.id).all()
    return {row[0]: row[1] for row in rows}


def _validate_category(db: Session, user: User, category_id: int | None) -> None:
    if category_id is not None:
        get_owned(db, Category, category_id, user)


@router.get("/links")
def transaction_links(db: Session = Depends(get_db), user: User = Depends(get_current_user)) -> dict:
    """Je Buchungs-ID die Gegenseite, falls sie Teil eines Übertrags ist.

    Getrennt vom Buchungs-Schema, damit dieses unverändert bleibt: Die
    Verknüpfung ist eine Schicht obendrauf, kein Feld der Buchung.
    """
    from ..services import uebertraege

    return {str(k): v for k, v in uebertraege.linkliste(db, user).items()}


@router.get("", response_model=list[TransactionOut])
def list_transactions(
    db: Session = Depends(get_db),
    user: User = Depends(get_current_user),
    account_id: int | None = None,
    category_id: int | None = None,
    # Zum Abarbeiten: nur Buchungen, die noch keine Kategorie haben. Überträge
    # bleiben aussen vor – sie ordnen kein Geld ein, sie verschieben es nur.
    uncategorized: bool = False,
    type: TxnType | None = None,
    date_from: date | None = None,
    date_to: date | None = None,
    # Großzügiges Limit: die Buchungsliste (DataTable) filtert/sortiert im Browser,
    # deshalb sollen standardmäßig ALLE Buchungen geladen werden, nicht nur 200.
    limit: int = Query(default=5000, le=50000),
    offset: int = 0,
):
    q = db.query(Transaction).filter(Transaction.owner_id == user.id)
    if account_id is not None:
        q = q.filter(
            (Transaction.account_id == account_id) | (Transaction.to_account_id == account_id)
        )
    if category_id is not None:
        q = q.filter(Transaction.category_id == category_id)
    if uncategorized:
        q = q.filter(Transaction.category_id.is_(None), Transaction.type != TxnType.transfer)
    if type is not None:
        q = q.filter(Transaction.type == type)
    if date_from is not None:
        q = q.filter(Transaction.date >= date_from)
    if date_to is not None:
        q = q.filter(Transaction.date <= date_to)
    rows = q.order_by(Transaction.date.desc(), Transaction.id.desc()).limit(limit).offset(offset).all()
    base = base_currency(db, user)
    ccy = _currency_map(db, user)
    return [to_out(db, t, base, ccy) for t in rows]


@router.post("", response_model=TransactionOut, status_code=status.HTTP_201_CREATED)
def create_transaction(
    payload: TransactionCreate, db: Session = Depends(get_db), user: User = Depends(get_current_user)
):
    from_acc = get_owned(db, Account, payload.account_id, user)
    to_acc = None
    category_id = payload.category_id

    if payload.type == TxnType.transfer:
        if payload.to_account_id is None or payload.to_account_id == payload.account_id:
            raise HTTPException(status.HTTP_400_BAD_REQUEST, "Transfer braucht ein anderes Zielkonto")
        to_acc = get_owned(db, Account, payload.to_account_id, user)
        category_id = None  # Transfers werden nicht regulär kategorisiert
    else:
        if payload.to_account_id is not None:
            raise HTTPException(status.HTTP_400_BAD_REQUEST, "Nur Transfers haben ein Zielkonto")
        _validate_category(db, user, category_id)

    _validate_category(db, user, payload.budget_category_id)

    txn = Transaction(
        owner_id=user.id,
        type=payload.type,
        date=payload.date,
        time=payload.time,
        account_id=from_acc.id,
        to_account_id=to_acc.id if to_acc else None,
        amount_cents=payload.amount_cents,
        to_amount_cents=payload.to_amount_cents,
        fx_rate=payload.fx_rate,
        category_id=category_id,
        budget_treatment=payload.budget_treatment,
        budget_category_id=payload.budget_category_id,
        payee=(payload.payee or None),
        description=(payload.description or None),
        notes=(payload.notes or None),
    )
    _recompute(db, txn, from_acc, to_acc)
    db.add(txn)
    db.commit()
    db.refresh(txn)
    return to_out(db, txn, base_currency(db, user), _currency_map(db, user))


@router.get("/{txn_id}", response_model=TransactionOut)
def get_transaction(
    txn_id: int, db: Session = Depends(get_db), user: User = Depends(get_current_user)
):
    txn = get_owned(db, Transaction, txn_id, user)
    return to_out(db, txn, base_currency(db, user), _currency_map(db, user))


@router.patch("/{txn_id}", response_model=TransactionOut)
def update_transaction(
    txn_id: int,
    payload: TransactionUpdate,
    db: Session = Depends(get_db),
    user: User = Depends(get_current_user),
):
    txn = get_owned(db, Transaction, txn_id, user)
    data = payload.model_dump(exclude_unset=True)

    for key in ("type", "date", "time", "amount_cents", "to_amount_cents", "fx_rate",
                "budget_treatment", "payee", "description", "notes"):
        if key in data:
            setattr(txn, key, data[key])

    if "account_id" in data and data["account_id"] is not None:
        get_owned(db, Account, data["account_id"], user)
        txn.account_id = data["account_id"]
    if "to_account_id" in data:
        if data["to_account_id"] is not None:
            get_owned(db, Account, data["to_account_id"], user)
        txn.to_account_id = data["to_account_id"]
    if "category_id" in data:
        _validate_category(db, user, data["category_id"])
        txn.category_id = data["category_id"]
    if "budget_category_id" in data:
        _validate_category(db, user, data["budget_category_id"])
        txn.budget_category_id = data["budget_category_id"]

    # Konsistenz je nach Typ + Neuberechnung der abgeleiteten Werte.
    from_acc = get_owned(db, Account, txn.account_id, user)
    to_acc = None
    if txn.type == TxnType.transfer:
        if txn.to_account_id is None or txn.to_account_id == txn.account_id:
            raise HTTPException(status.HTTP_400_BAD_REQUEST, "Transfer braucht ein anderes Zielkonto")
        to_acc = get_owned(db, Account, txn.to_account_id, user)
        txn.category_id = None
    else:
        txn.to_account_id = None
    _recompute(db, txn, from_acc, to_acc)

    db.commit()
    db.refresh(txn)
    return to_out(db, txn, base_currency(db, user), _currency_map(db, user))


@router.delete("/{txn_id}", status_code=status.HTTP_204_NO_CONTENT)
def delete_transaction(
    txn_id: int, db: Session = Depends(get_db), user: User = Depends(get_current_user)
):
    txn = get_owned(db, Transaction, txn_id, user)
    db.delete(txn)
    db.commit()