import math
from collections import defaultdict
from datetime import date, timedelta
from typing import Callable

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

from ..database import get_db
from ..deps import get_current_user
from ..models import (
    Group,
    GroupLocationMinStock,
    Item,
    Location,
    Lot,
    Movement,
    PackageType,
    Product,
    ProductLocationMinStock,
    User,
)
from ..schemas import (
    BaseUnit,
    ExpiringItem,
    GroupShoppingItem,
    LocationContentEntry,
    LocationContents,
    LocationNeedGroup,
    LocationNeedProduct,
    LocationNeeds,
    MovementOut,
    ShoppingItem,
    ShoppingListAll,
    ShoppingNeed,
)
from ..services.conversion import BASE_OF_KIND, article_unit, display_unit_info
from ..services.stock import (
    current_stock,
    descendant_location_ids,
    location_subtree_stock_base,
)
from .settings import get_expiry_warning_days

router = APIRouter(tags=["views"])


# ---- Bedarf lesbar aufbereiten (Gebinde als Leitangabe) --------------------
_UNIT_SHORT: dict[BaseUnit, str] = {
    BaseUnit.piece: "Stk",
    BaseUnit.gram: "g",
    BaseUnit.milliliter: "ml",
}


def _de_num(x: float) -> str:
    """Deutsche Kurzzahl ohne unnoetige Nullen: 500, 1, 1,4."""
    r = round(float(x), 2)
    if r == int(r):
        return str(int(r))
    return f"{r:.2f}".rstrip("0").rstrip(".").replace(".", ",")


def _package_plural(db: Session) -> dict[str, str]:
    """Einzahl -> Mehrzahl der Gebinde (Glas -> Gläser), aus der Gebinde-Tabelle."""
    return {pt.singular: pt.plural for pt in db.query(PackageType).all()}


def _uniform_package(products: list[Product]) -> tuple[float, str] | None:
    """Gemeinsames Gebinde einer Produktmenge – nur wenn *alle* dasselbe haben.

    Für eine Gruppe lässt sich „x Gläser" nur dann eindeutig sagen, wenn jedes
    passende Produkt dieselbe Packungsgröße und -bezeichnung trägt. Sonst bleibt
    es bei der Basiseinheit."""
    if not products:
        return None
    combos = {(p.package_size, p.package_label or "Packung") for p in products}
    if len(combos) == 1:
        size, label = next(iter(combos))
        if size and size > 0:
            return float(size), label
    return None


def _build_need(
    *,
    deficit_base: float,
    stock_base: float,
    min_base: float,
    factor: float,
    singular: str,
    is_package: bool,
    base_unit: BaseUnit | None,
    plural: dict[str, str],
) -> ShoppingNeed:
    """Rechnet Basiseinheiten in Gebinde/Artikeleinheiten um und baut die Texte.

    ``factor`` = Basiseinheiten je Gebinde (Packungsgröße bzw. Einheitenfaktor).
    Bei zählbaren Packungen wird die Kaufmenge auf ganze Gebinde aufgerundet."""
    f = factor or 1.0
    count = math.ceil(deficit_base / f - 1e-9) if is_package else round(deficit_base / f, 3)
    label = singular if abs(count) == 1 else plural.get(singular, singular)
    text = f"{_de_num(count)} {label}".strip()
    hint = ""
    base_amount: float | None = None
    if (is_package or f != 1.0) and base_unit is not None:
        base_amount = round(deficit_base, 3)
        hint = f"{_de_num(deficit_base)} {_UNIT_SHORT.get(base_unit, base_unit.value)}"
    return ShoppingNeed(
        text=text,
        hint=hint,
        count=count,
        label=label,
        singular=singular,
        is_package=is_package,
        base_amount=base_amount,
        base_unit=base_unit if base_amount is not None else None,
        stock=round(stock_base / f, 3),
        min_stock=round(min_base / f, 3),
    )


def _gruppen_bedarf(
    *,
    deficit_unit: float,
    stock_unit: float,
    min_unit: float,
    divisor: float,
    unit_name: str,
    base_unit: BaseUnit | None,
    products: list[Product],
    plural: dict[str, str],
) -> ShoppingNeed:
    """Bedarf einer Gruppe. Mengen kommen in der Gruppen-Einheit (``unit_name``);
    ``divisor`` rechnet sie in Basiseinheiten zurück. Haben alle passenden
    Produkte dasselbe Gebinde, wird als Leitangabe dieses Gebinde (z.B. Gläser)
    genutzt, sonst die Gruppen-Einheit selbst."""
    pkg = _uniform_package(products) if base_unit is not None else None
    if pkg is not None:
        factor, singular, is_package = pkg[0], pkg[1], True
    else:
        factor, singular, is_package = (divisor or 1.0), unit_name, False
    return _build_need(
        deficit_base=deficit_unit * divisor,
        stock_base=stock_unit * divisor,
        min_base=min_unit * divisor,
        factor=factor,
        singular=singular,
        is_package=is_package,
        base_unit=base_unit,
        plural=plural,
    )


@router.get("/shopping-list", response_model=list[ShoppingItem])
def shopping_list(
    db: Session = Depends(get_db), _: User = Depends(get_current_user)
) -> list[ShoppingItem]:
    """Produkte, deren Bestand unter dem Mindestbestand liegt."""
    plural = _package_plural(db)
    items: list[ShoppingItem] = []
    products = (
        db.query(Product)
        .filter(Product.min_stock.isnot(None), Product.min_stock > 0)
        .all()
    )
    for product in products:
        stock = current_stock(db, product.id)
        if stock < product.min_stock:
            factor, singular = article_unit(product)
            items.append(
                ShoppingItem(
                    product_id=product.id,
                    name=product.name,
                    base_unit=product.base_unit,
                    package_size=product.package_size,
                    stock=stock,
                    min_stock=product.min_stock,
                    deficit=product.min_stock - stock,
                    need=_build_need(
                        deficit_base=product.min_stock - stock,
                        stock_base=stock,
                        min_base=product.min_stock,
                        factor=factor,
                        singular=singular,
                        is_package=bool(product.package_size and product.package_size > 0),
                        base_unit=product.base_unit,
                        plural=plural,
                    ),
                )
            )
    items.sort(key=lambda i: i.deficit, reverse=True)
    return items


@router.get("/shopping-list/groups", response_model=list[GroupShoppingItem])
def group_shopping_list(
    db: Session = Depends(get_db), _: User = Depends(get_current_user)
) -> list[GroupShoppingItem]:
    """Gruppen, deren Gesamtbestand unter dem Gruppen-Mindestbestand liegt.

    Gruppen-Bestand = Summe der Produktbestände in der Gruppe (in Basiseinheiten).
    Sinnvoll, wenn die Produkte einer Gruppe dieselbe Basiseinheit teilen.
    """
    plural = _package_plural(db)
    items: list[GroupShoppingItem] = []
    groups = (
        db.query(Group).filter(Group.min_stock.isnot(None), Group.min_stock > 0).all()
    )
    for group in groups:
        unit = group.min_stock_unit
        if unit is not None:
            base = BASE_OF_KIND[unit.kind]
            products = [p for p in group.products if p.base_unit == base]
            divisor = unit.factor
            stock = float(sum(current_stock(db, p.id) for p in products)) / divisor
            unit_name = unit.name
            base_unit: BaseUnit | None = base
        else:
            products = list(group.products)
            divisor = 1.0
            stock = float(sum(current_stock(db, p.id) for p in products))
            unit_name = ""
            base_unit = None
        if stock < group.min_stock:
            deficit = group.min_stock - stock
            items.append(
                GroupShoppingItem(
                    group_id=group.id,
                    name=group.name,
                    stock=stock,
                    min_stock=group.min_stock,
                    deficit=deficit,
                    unit_name=unit_name,
                    product_count=len(products),
                    need=_gruppen_bedarf(
                        deficit_unit=deficit,
                        stock_unit=stock,
                        min_unit=group.min_stock,
                        divisor=divisor,
                        unit_name=unit_name,
                        base_unit=base_unit,
                        products=products,
                        plural=plural,
                    ),
                )
            )
    items.sort(key=lambda i: i.deficit, reverse=True)
    return items


def _netted_topups(
    db: Session, locs_min: dict[str, float], stock_of: Callable[[str], float]
) -> dict[str, float]:
    """Bedarf je Ort mit verschachtelten Orten verrechnet: Was in einen Unterort
    gekauft wird, liegt auch im Subtree des Oberorts und deckt dessen Bedarf mit.
    ``topup(ort)`` ist die je Ort ZUSÄTZLICH nötige Menge – über die Käufe in den
    Unterorten hinaus. So kostet „Lemgo braucht 5, Küche braucht 2" bei je 1 fehlend
    nur 1 (in die Küche), nicht 2."""
    locs = list(locs_min)
    # Nachkommen-Bedarfsorte je Ort (im Lagerort-Baum), memoisiert von unten nach oben.
    desc = {
        loc: [d for d in locs if d != loc and d in descendant_location_ids(db, loc)]
        for loc in locs
    }
    memo: dict[str, float] = {}

    def topup(loc: str) -> float:
        if loc not in memo:
            committed = sum(topup(d) for d in desc[loc])
            memo[loc] = max(0.0, locs_min[loc] - (stock_of(loc) + committed))
        return memo[loc]

    return {loc: topup(loc) for loc in locs}


@router.get("/shopping-list/by-location", response_model=list[LocationNeeds])
def shopping_list_by_location(
    db: Session = Depends(get_db), _: User = Depends(get_current_user)
) -> list[LocationNeeds]:
    """Bedarfe je Lagerort: Produkte und Gruppen, deren Bestand AN DIESEM ORT
    unter dem dort hinterlegten Mindestbestand liegt."""
    plural = _package_plural(db)
    prod_needs: dict[str, list[LocationNeedProduct]] = defaultdict(list)
    group_needs: dict[str, list[LocationNeedGroup]] = defaultdict(list)

    # Je Produkt alle Ort-Mindestbestände sammeln und hierarchisch verrechnen.
    prod_by_id: dict[int, list[ProductLocationMinStock]] = defaultdict(list)
    for e in db.query(ProductLocationMinStock).all():
        prod_by_id[e.product_id].append(e)
    for product_id, entries in prod_by_id.items():
        product = db.get(Product, product_id)
        if product is None:
            continue
        faktor, label = article_unit(product)
        faktor = faktor or 1.0
        ist_gebinde = bool(product.package_size and product.package_size > 0)
        locs_min = {e.location_id: e.min_stock for e in entries}
        bestand = {loc: location_subtree_stock_base(db, product, loc) / faktor for loc in locs_min}
        for loc, need in _netted_topups(db, locs_min, bestand.__getitem__).items():
            if need > 1e-9:
                prod_needs[loc].append(LocationNeedProduct(
                    product_id=product.id, name=product.name, unit_label=label,
                    stock=round(bestand[loc], 3), min_stock=locs_min[loc],
                    deficit=round(need, 3),
                    # Mengen liegen hier in Artikeleinheiten -> * faktor = Basiseinheiten.
                    need=_build_need(
                        deficit_base=need * faktor,
                        stock_base=bestand[loc] * faktor,
                        min_base=locs_min[loc] * faktor,
                        factor=faktor,
                        singular=label,
                        is_package=ist_gebinde,
                        base_unit=product.base_unit,
                        plural=plural,
                    ),
                ))

    # Je Gruppe genauso – Bestand je Ort ist die Summe der passenden Produkte im Subtree.
    group_by_id: dict[int, list[GroupLocationMinStock]] = defaultdict(list)
    for e in db.query(GroupLocationMinStock).all():
        group_by_id[e.group_id].append(e)
    for group_id, entries in group_by_id.items():
        group = db.get(Group, group_id)
        if group is None:
            continue
        unit = group.min_stock_unit
        if unit is not None:
            base = BASE_OF_KIND[unit.kind]
            matching = [p for p in group.products if p.base_unit == base]
            divisor, unit_name = unit.factor, unit.name
            g_base_unit: BaseUnit | None = base
        else:
            matching, divisor, unit_name = list(group.products), 1.0, ""
            g_base_unit = None
        locs_min = {e.location_id: e.min_stock for e in entries}
        bestand = {
            loc: sum(location_subtree_stock_base(db, p, loc) for p in matching) / divisor
            for loc in locs_min
        }
        for loc, need in _netted_topups(db, locs_min, bestand.__getitem__).items():
            if need > 1e-9:
                group_needs[loc].append(LocationNeedGroup(
                    group_id=group.id, name=group.name, unit_name=unit_name,
                    stock=round(bestand[loc], 3), min_stock=locs_min[loc],
                    deficit=round(need, 3),
                    need=_gruppen_bedarf(
                        deficit_unit=need,
                        stock_unit=bestand[loc],
                        min_unit=locs_min[loc],
                        divisor=divisor,
                        unit_name=unit_name,
                        base_unit=g_base_unit,
                        products=matching,
                        plural=plural,
                    ),
                ))

    loc_ids = set(prod_needs) | set(group_needs)
    namen = {
        loc.id: loc.name
        for loc in db.query(Location).filter(Location.id.in_(loc_ids)).all()
    }
    result: list[LocationNeeds] = []
    for loc_id in sorted(loc_ids, key=lambda i: namen.get(i, "")):
        result.append(LocationNeeds(
            location_id=loc_id,
            location_name=namen.get(loc_id, "?"),
            products=sorted(prod_needs.get(loc_id, []), key=lambda x: x.deficit, reverse=True),
            groups=sorted(group_needs.get(loc_id, []), key=lambda x: x.deficit, reverse=True),
        ))
    return result


@router.get("/shopping-list/all", response_model=ShoppingListAll)
def shopping_list_all(
    db: Session = Depends(get_db), user: User = Depends(get_current_user)
) -> ShoppingListAll:
    """Komplette Einkaufsliste in einem Aufruf: Produkte, Gruppen und Bedarfe je
    Lagerort – genau die drei Quellen, die auch die Oberfläche zusammenführt.
    Erspart drei getrennte Abfragen."""
    return ShoppingListAll(
        products=shopping_list(db, user),
        groups=group_shopping_list(db, user),
        by_location=shopping_list_by_location(db, user),
    )


@router.get("/location/{code}", response_model=LocationContents)
def location_contents(
    code: str,
    db: Session = Depends(get_db),
    _: User = Depends(get_current_user),
) -> LocationContents:
    """Alle Artikel, die an einem Lagerort liegen – inklusive der Unterorte.

    Ziel des Lagerort-QR (`/l/<code>`) beim Nachschlagen: einmal scannen und
    sehen, was im Regal/Fach (und allem darunter) steht. Zählt sowohl
    Lot-Bestände (Lebensmittel/Objekte) als auch Einzelstücke.
    """
    loc = db.get(Location, code)
    if loc is None:
        raise HTTPException(status.HTTP_404_NOT_FOUND, "Lagerort nicht gefunden")

    ids = {code} | descendant_location_ids(db, code)
    product_ids: set[int] = {
        pid for (pid,) in db.query(Lot.product_id).filter(Lot.location_id.in_(ids)).distinct()
    }
    product_ids |= {
        pid for (pid,) in db.query(Item.product_id).filter(Item.location_id.in_(ids)).distinct()
    }

    entries: list[LocationContentEntry] = []
    for pid in product_ids:
        product = db.get(Product, pid)
        if product is None:
            continue
        faktor, label = article_unit(product)
        stock = location_subtree_stock_base(db, product, code) / (faktor or 1.0)
        if stock <= 0:
            continue
        entries.append(LocationContentEntry(
            product_id=product.id, name=product.name, brand=product.brand,
            stock=round(stock, 3), unit_label=label, individual=product.individual,
        ))
    entries.sort(key=lambda e: e.name.lower())
    return LocationContents(location_id=code, location_name=loc.name, products=entries)


@router.get("/expiring", response_model=list[ExpiringItem])
def expiring(
    days: int | None = None,
    db: Session = Depends(get_db),
    _: User = Depends(get_current_user),
) -> list[ExpiringItem]:
    """Chargen, die innerhalb der Warnfrist ablaufen (oder schon abgelaufen sind)."""
    if days is None:
        days = get_expiry_warning_days(db)
    today = date.today()
    threshold = today + timedelta(days=days)

    lots = (
        db.query(Lot)
        .filter(Lot.best_before.isnot(None), Lot.best_before <= threshold, Lot.quantity > 0)
        .order_by(Lot.best_before)
        .all()
    )
    result: list[ExpiringItem] = []
    for lot in lots:
        product = lot.product
        unit_name, unit_factor = display_unit_info(product)
        result.append(
            ExpiringItem(
                lot_id=lot.id,
                product_id=product.id,
                product_name=product.name,
                quantity=lot.quantity,
                base_unit=product.base_unit,
                best_before=lot.best_before,
                best_before_precision=lot.best_before_precision,
                days_left=(lot.best_before - today).days,
                package_size=product.package_size,
                package_label=product.package_label,
                unit_name=unit_name,
                unit_factor=unit_factor,
            )
        )
    return result


@router.get("/movements", response_model=list[MovementOut])
def movements(
    limit: int = 100,
    product_id: int | None = None,
    db: Session = Depends(get_db),
    _: User = Depends(get_current_user),
) -> list[MovementOut]:
    """Bewegungsverlauf (wer hat wann was ein-/ausgelagert), neueste zuerst."""
    limit = max(1, min(limit, 500))
    query = (
        db.query(Movement, Product, User)
        .join(Product, Movement.product_id == Product.id)
        .outerjoin(User, Movement.user_id == User.id)
    )
    if product_id is not None:
        query = query.filter(Movement.product_id == product_id)
    rows = query.order_by(Movement.created_at.desc(), Movement.id.desc()).limit(limit).all()

    result: list[MovementOut] = []
    for movement, product, user in rows:
        unit_name, unit_factor = display_unit_info(product)
        result.append(
            MovementOut(
                id=movement.id,
                product_id=product.id,
                product_name=product.name,
                type=movement.type.value,
                quantity=movement.quantity,
                base_unit=product.base_unit,
                unit_used=movement.unit_used,
                username=user.username if user else None,
                note=movement.note,
                created_at=movement.created_at,
                package_size=product.package_size,
                package_label=product.package_label,
                unit_name=unit_name,
                unit_factor=unit_factor,
            )
        )
    return result