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

from ..database import get_db
from ..deps import get_current_user, require_admin
from ..models import Barcode, Group, Product, User
from ..schemas import (
    BarcodeCreate,
    BarcodeNoteUpdate,
    BarcodeOut,
    GroupCreate,
    GroupOut,
    GroupUpdate,
    ProductBarcodeOut,
)
from ..services.conversion import BASE_OF_KIND
from ..services.stock import current_stock

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


def _group_to_out(db: Session, group: Group) -> GroupOut:
    out = GroupOut.model_validate(group)
    products = db.query(Product).filter(Product.group_id == group.id).all()
    out.product_count = len(products)
    out.barcodes = [
        BarcodeOut.model_validate(b)
        for b in db.query(Barcode).filter(Barcode.group_id == group.id).order_by(Barcode.id).all()
    ]
    # Codes der Artikel in dieser Gruppe mitliefern. Sie waren bisher nirgends
    # sichtbar, wodurch eine Kategorie mit Artikeln "0 EANs" anzeigte.
    product_codes: list[ProductBarcodeOut] = []
    for product in products:
        if product.barcode:
            product_codes.append(
                ProductBarcodeOut(
                    code=product.barcode, product_id=product.id, product_name=product.name
                )
            )
        for alias in db.query(Barcode).filter(Barcode.product_id == product.id).order_by(Barcode.id):
            product_codes.append(
                ProductBarcodeOut(
                    code=alias.code, product_id=product.id, product_name=product.name
                )
            )
    out.product_barcodes = product_codes

    unit = group.min_stock_unit
    if unit is not None:
        # Bestand nur über Produkte gleicher Art, in der Gruppen-Einheit ausgedrückt.
        base = BASE_OF_KIND[unit.kind]
        matching = [p for p in products if p.base_unit == base]
        stock_base = float(sum(current_stock(db, p.id) for p in matching))
        out.stock = stock_base / unit.factor
        out.min_stock_unit_name = unit.name
        out.kind = unit.kind.value
    else:
        out.stock = float(sum(current_stock(db, p.id) for p in products))
    return out


@router.get("", response_model=list[GroupOut])
def list_groups(
    db: Session = Depends(get_db), _: User = Depends(get_current_user)
) -> list[GroupOut]:
    groups = db.query(Group).order_by(Group.name).all()
    return [_group_to_out(db, g) for g in groups]


@router.post("", response_model=GroupOut, status_code=status.HTTP_201_CREATED)
def create_group(
    payload: GroupCreate,
    db: Session = Depends(get_db),
    _: User = Depends(require_admin),
) -> GroupOut:
    if db.query(Group).filter(Group.name == payload.name).first():
        raise HTTPException(status.HTTP_409_CONFLICT, "Gruppe existiert bereits")
    group = Group(
        name=payload.name,
        min_stock=payload.min_stock,
        min_stock_unit_id=payload.min_stock_unit_id,
    )
    db.add(group)
    db.commit()
    db.refresh(group)
    return _group_to_out(db, group)


@router.patch("/{group_id}", response_model=GroupOut)
def update_group(
    group_id: int,
    payload: GroupUpdate,
    db: Session = Depends(get_db),
    _: User = Depends(require_admin),
) -> GroupOut:
    group = db.get(Group, group_id)
    if group is None:
        raise HTTPException(status.HTTP_404_NOT_FOUND, "Gruppe nicht gefunden")
    data = payload.model_dump(exclude_unset=True)
    if "name" in data and data["name"]:
        clash = (
            db.query(Group)
            .filter(Group.name == data["name"], Group.id != group_id)
            .first()
        )
        if clash:
            raise HTTPException(status.HTTP_409_CONFLICT, "Name bereits vergeben")
    for field, value in data.items():
        setattr(group, field, value)
    db.commit()
    db.refresh(group)
    return _group_to_out(db, group)


def _describe_conflict(db: Session, code: str, group_id: int) -> str | None:
    """Sagt, wem ein Code schon gehört – "bereits vergeben" allein half nicht weiter."""
    product = db.query(Product).filter(Product.barcode == code).first()
    existing = db.query(Barcode).filter(Barcode.code == code).first()

    if existing is not None and existing.product_id:
        product = db.get(Product, existing.product_id) or product

    if product is not None:
        if product.group_id == group_id:
            # Der Code steht durch den Artikel ohnehin schon in dieser Gruppe.
            return (
                f"Dieser Code gehört zum Artikel \"{product.name}\" und ist über ihn "
                "bereits in dieser Gruppe."
            )
        if product.group_id is not None:
            other = db.get(Group, product.group_id)
            name = other.name if other else "einer anderen Gruppe"
            return (
                f"Dieser Code gehört zum Artikel \"{product.name}\", der in der Gruppe "
                f"\"{name}\" liegt. Ändere die Gruppe des Artikels, statt den Code hier "
                "einzutragen."
            )
        return (
            f"Dieser Code gehört bereits zum Artikel \"{product.name}\". Ordne den "
            "Artikel dieser Gruppe zu – sein Code erscheint dann automatisch hier."
        )

    if existing is not None and existing.group_id == group_id:
        return "Dieser Code ist in dieser Gruppe bereits hinterlegt."
    if existing is not None and existing.group_id:
        other = db.get(Group, existing.group_id)
        name = other.name if other else "einer anderen Gruppe"
        return f"Dieser Code ist bereits der Gruppe \"{name}\" zugeordnet."
    if existing is not None:
        return "Dieser Code ist bereits vergeben."
    return None


@router.post("/{group_id}/barcodes", response_model=GroupOut, status_code=status.HTTP_201_CREATED)
def add_group_barcode(
    group_id: int,
    payload: BarcodeCreate,
    db: Session = Depends(get_db),
    _: User = Depends(require_admin),
) -> GroupOut:
    """EAN einer Gruppe zuordnen (z.B. alle Mehl-Marken zur Gruppe "Mehl")."""
    group = db.get(Group, group_id)
    if group is None:
        raise HTTPException(status.HTTP_404_NOT_FOUND, "Gruppe nicht gefunden")
    code = payload.code.strip()
    conflict = _describe_conflict(db, code, group.id)
    if conflict:
        raise HTTPException(status.HTTP_409_CONFLICT, conflict)
    db.add(Barcode(code=code, note=(payload.note or None), group_id=group.id))
    db.commit()
    db.refresh(group)
    return _group_to_out(db, group)


@router.patch("/{group_id}/barcodes/{code}", response_model=GroupOut)
def update_group_barcode_note(
    group_id: int,
    code: str,
    payload: BarcodeNoteUpdate,
    db: Session = Depends(get_db),
    _: User = Depends(require_admin),
) -> GroupOut:
    """Notiz zu einem Gruppen-Code setzen.

    Betrifft ausdrücklich auch Codes, die beim Zuordnen eines Artikels
    automatisch entstanden sind – die hatten bisher gar keine Möglichkeit,
    eine Notiz zu bekommen.
    """
    group = db.get(Group, group_id)
    if group is None:
        raise HTTPException(status.HTTP_404_NOT_FOUND, "Gruppe nicht gefunden")
    entry = (
        db.query(Barcode).filter(Barcode.group_id == group_id, Barcode.code == code).first()
    )
    if entry is None:
        raise HTTPException(status.HTTP_404_NOT_FOUND, "Code nicht gefunden")

    note = (payload.note or "").strip()
    entry.note = note or None
    db.commit()
    db.refresh(group)
    return _group_to_out(db, group)


@router.delete("/{group_id}/barcodes/{code}", status_code=status.HTTP_204_NO_CONTENT)
def delete_group_barcode(
    group_id: int,
    code: str,
    db: Session = Depends(get_db),
    _: User = Depends(require_admin),
) -> None:
    entry = (
        db.query(Barcode).filter(Barcode.group_id == group_id, Barcode.code == code).first()
    )
    if entry is None:
        raise HTTPException(status.HTTP_404_NOT_FOUND, "Code nicht gefunden")
    db.delete(entry)
    db.commit()


@router.delete("/{group_id}", status_code=status.HTTP_204_NO_CONTENT)
def delete_group(
    group_id: int,
    db: Session = Depends(get_db),
    _: User = Depends(require_admin),
) -> None:
    group = db.get(Group, group_id)
    if group is None:
        raise HTTPException(status.HTTP_404_NOT_FOUND, "Gruppe nicht gefunden")
    db.delete(group)
    db.commit()