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 pydantic import BaseModel
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 buchung, currency, uebertrag_buchen
from ..services.uebertrag_buchen import UebertragFehler
from .accounts import base_currency

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


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=buchung.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),
    )
    buchung.setze_betraege(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
    buchung.setze_betraege(db, txn, from_acc, to_acc)

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


class TransactionTransferIn(BaseModel):
    to_account_id: int
    # Nur setzen, wenn man es besser weiss als Certain – siehe uebertrag_buchen.
    trotzdem: bool = False


@router.post("/{txn_id}/transfer", response_model=TransactionOut)
def make_transfer(txn_id: int, payload: TransactionTransferIn,
                  db: Session = Depends(get_db), user: User = Depends(get_current_user)):
    """Eine gebuchte Ausgabe oder Einnahme zum Kontoübertrag machen.

    Nicht über PATCH: Der dreht die Richtung bei einer Einnahme nicht um und
    legt keine Gegenseite auf dem Zielkonto an. Beides gehört zusammen, deshalb
    läuft es durch denselben Dienst wie der Weg aus dem Eingang.
    """
    txn = get_owned(db, Transaction, txn_id, user)
    ziel = get_owned(db, Account, payload.to_account_id, user)
    try:
        uebertrag_buchen.aus_buchung(db, user, txn, ziel, payload.trotzdem)
    except UebertragFehler as e:
        db.rollback()
        raise HTTPException(
            status_code=status.HTTP_409_CONFLICT if e.nachfragen
            else status.HTTP_400_BAD_REQUEST,
            detail=str(e),
        ) from e
    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()