Vorrania/backend/app/services/stock.py

"""Chargen-Logik: Einlagern erzeugt Lots, Auslagern bucht per FEFO ab."""

from __future__ import annotations

from datetime import date

from sqlalchemy import asc
from sqlalchemy.orm import Session

from ..models import Lot, Movement, MovementType, Product, User
from .conversion import to_base


class StockError(ValueError):
    """Fachlicher Fehler beim Ein-/Auslagern (z.B. zu wenig Bestand)."""


def current_stock(db: Session, product_id: int) -> float:
    """Summe der Lot-Mengen eines Produkts (in Basiseinheiten)."""
    total = (
        db.query(Lot).with_entities(Lot.quantity).filter(Lot.product_id == product_id).all()
    )
    return float(sum(q for (q,) in total))


def check_in(
    db: Session,
    product: Product,
    quantity: float,
    unit: str,
    best_before: date | None,
    location_id: int | None,
    user: User | None,
    note: str | None = None,
) -> Lot:
    """Legt eine neue Charge an und protokolliert die Bewegung."""
    quantity_base = to_base(db, product, quantity, unit)

    lot = Lot(
        product_id=product.id,
        quantity=quantity_base,
        best_before=best_before,
        location_id=location_id,
    )
    db.add(lot)
    db.flush()  # lot.id verfügbar machen

    db.add(
        Movement(
            product_id=product.id,
            lot_id=lot.id,
            user_id=user.id if user else None,
            type=MovementType.in_,
            quantity=quantity_base,
            unit_used=unit,
            note=note,
        )
    )
    return lot


def check_out_lot(
    db: Session,
    product: Product,
    lot: Lot,
    quantity: float,
    unit: str,
    user: User | None,
    note: str | None = None,
) -> list[dict]:
    """Bucht gezielt von EINER Charge ab (manuelle Auswahl statt FEFO)."""
    needed = to_base(db, product, quantity, unit)
    if needed > lot.quantity + 1e-9:
        raise StockError(
            f"Diese Charge hat nur {lot.quantity:g} {product.base_unit.value} "
            f"(benötigt {needed:g})."
        )

    lot.quantity -= needed
    db.add(
        Movement(
            product_id=product.id,
            lot_id=lot.id,
            user_id=user.id if user else None,
            type=MovementType.out,
            quantity=needed,
            unit_used=unit,
            note=note,
        )
    )
    affected = [{"lot_id": lot.id, "quantity": needed}]
    if lot.quantity <= 1e-9:
        db.delete(lot)
    return affected


def _fefo_lots(db: Session, product_id: int) -> list[Lot]:
    """Lots eines Produkts, sortiert nach Ablaufdatum (NULL zuletzt), dann Alter."""
    lots = (
        db.query(Lot)
        .filter(Lot.product_id == product_id, Lot.quantity > 0)
        .order_by(asc(Lot.created_at))
        .all()
    )
    # NULL-best_before ans Ende (nach Datum aufsteigend). In Python sortieren, damit
    # es über SQLite und Postgres identisch funktioniert.
    return sorted(
        lots,
        key=lambda lot: (lot.best_before is None, lot.best_before or date.max, lot.id),
    )


def check_out(
    db: Session,
    product: Product,
    quantity: float,
    unit: str,
    user: User | None,
    note: str | None = None,
) -> list[dict]:
    """Bucht ``quantity`` (in ``unit``) per FEFO von den Chargen ab.

    Gibt die Liste der betroffenen Chargen mit abgebuchter Menge zurück.
    Wirft StockError, wenn der Gesamtbestand nicht ausreicht.
    """
    needed = to_base(db, product, quantity, unit)
    available = current_stock(db, product.id)
    if needed > available + 1e-9:
        raise StockError(
            f"Nicht genug Bestand: benötigt {needed:g}, verfügbar {available:g} "
            f"{product.base_unit.value}"
        )

    affected: list[dict] = []
    remaining = needed
    for lot in _fefo_lots(db, product.id):
        if remaining <= 1e-9:
            break
        take = min(lot.quantity, remaining)
        lot.quantity -= take
        remaining -= take

        db.add(
            Movement(
                product_id=product.id,
                lot_id=lot.id,
                user_id=user.id if user else None,
                type=MovementType.out,
                quantity=take,
                unit_used=unit,
                note=note,
            )
        )
        affected.append({"lot_id": lot.id, "quantity": take})

        # Leere Charge entfernen, damit das "MHD-Array" sauber bleibt.
        if lot.quantity <= 1e-9:
            db.delete(lot)

    return affected