from __future__ import annotations

import enum
from datetime import date, datetime, timezone

from sqlalchemy import (
    Boolean,
    Date,
    DateTime,
    Enum,
    Float,
    ForeignKey,
    Integer,
    String,
    Text,
    UniqueConstraint,
)
from sqlalchemy.orm import Mapped, mapped_column, relationship

from .database import Base


def _now() -> datetime:
    return datetime.now(timezone.utc)


class Role(str, enum.Enum):
    admin = "admin"
    user = "user"


class BaseUnit(str, enum.Enum):
    piece = "piece"
    gram = "gram"
    milliliter = "milliliter"


class MovementType(str, enum.Enum):
    in_ = "in"
    out = "out"
    adjust = "adjust"


class UnitKind(str, enum.Enum):
    """Art einer Einheit. Bestimmt die kanonische Basiseinheit für die Speicherung."""
    count = "count"      # Basis: Stück
    weight = "weight"    # Basis: Gramm
    volume = "volume"    # Basis: Milliliter


class Unit(Base):
    """Vom Admin verwaltbare Einheit mit Umrechnungsfaktor zur kanonischen Basis.

    factor = wie viele Basiseinheiten 1 dieser Einheit entsprechen
    (z.B. Kilogramm: kind=weight, factor=1000; Liter: kind=volume, factor=1000).
    """
    __tablename__ = "units"

    id: Mapped[int] = mapped_column(Integer, primary_key=True)
    name: Mapped[str] = mapped_column(String(64), unique=True, nullable=False)
    kind: Mapped[UnitKind] = mapped_column(Enum(UnitKind), nullable=False)
    factor: Mapped[float] = mapped_column(Float, nullable=False, default=1.0)
    is_builtin: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)


class User(Base):
    __tablename__ = "users"

    id: Mapped[int] = mapped_column(Integer, primary_key=True)
    username: Mapped[str] = mapped_column(String(64), unique=True, nullable=False)
    password_hash: Mapped[str] = mapped_column(String(255), nullable=False)
    role: Mapped[Role] = mapped_column(Enum(Role), nullable=False, default=Role.user)
    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)


class Group(Base):
    __tablename__ = "groups"

    id: Mapped[int] = mapped_column(Integer, primary_key=True)
    name: Mapped[str] = mapped_column(String(120), unique=True, nullable=False)
    min_stock: Mapped[float | None] = mapped_column(Float, nullable=True)
    # Einheit des Gruppen-Mindestbestands (z.B. Kilogramm). NULL = zählt in Basiseinheiten.
    min_stock_unit_id: Mapped[int | None] = mapped_column(
        ForeignKey("units.id", ondelete="SET NULL"), nullable=True
    )

    products: Mapped[list[Product]] = relationship(back_populates="group")
    min_stock_unit: Mapped[Unit | None] = relationship()


class Location(Base):
    __tablename__ = "locations"

    id: Mapped[int] = mapped_column(Integer, primary_key=True)
    name: Mapped[str] = mapped_column(String(120), nullable=False)
    # Sub-locations (Regal/Fach) are a Schritt-3 feature; parent_id kept for forward-compat.
    parent_id: Mapped[int | None] = mapped_column(
        ForeignKey("locations.id", ondelete="SET NULL"), nullable=True
    )


class Product(Base):
    __tablename__ = "products"
    __table_args__ = (UniqueConstraint("barcode", name="uq_products_barcode"),)

    id: Mapped[int] = mapped_column(Integer, primary_key=True)
    barcode: Mapped[str | None] = mapped_column(String(64), nullable=True)
    name: Mapped[str] = mapped_column(String(255), nullable=False)
    brand: Mapped[str | None] = mapped_column(String(255), nullable=True)
    image_url: Mapped[str | None] = mapped_column(String(1024), nullable=True)

    # Kanonische Basiseinheit (piece/gram/milliliter): bestimmt Speicherung + Art (kind).
    base_unit: Mapped[BaseUnit] = mapped_column(
        Enum(BaseUnit), nullable=False, default=BaseUnit.piece
    )
    # Bevorzugte Anzeige-/Eingabeeinheit (z.B. Kilogramm). NULL = Basiseinheit selbst.
    display_unit_id: Mapped[int | None] = mapped_column(
        ForeignKey("units.id", ondelete="SET NULL"), nullable=True
    )
    # Number of base units contained in one package (e.g. 500 g per package).
    package_size: Mapped[float | None] = mapped_column(Float, nullable=True)
    # Bezeichnung eines Gebindes: "Packung", "Glas", "Tüte", "Flasche", …
    package_label: Mapped[str | None] = mapped_column(String(32), nullable=True)

    group_id: Mapped[int | None] = mapped_column(
        ForeignKey("groups.id", ondelete="SET NULL"), nullable=True
    )
    min_stock: Mapped[float | None] = mapped_column(Float, nullable=True)  # in base units
    # In welcher Einheit der Mindestbestand erfasst wurde (nur für die Anzeige).
    min_stock_unit_id: Mapped[int | None] = mapped_column(
        ForeignKey("units.id", ondelete="SET NULL"), nullable=True
    )
    min_stock_in_packages: Mapped[bool] = mapped_column(
        Boolean, nullable=False, default=False
    )

    source: Mapped[str] = mapped_column(String(16), nullable=False, default="manual")
    off_raw: Mapped[str | None] = mapped_column(Text, nullable=True)  # JSON blob from OFF
    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)

    group: Mapped[Group | None] = relationship(back_populates="products")
    display_unit: Mapped[Unit | None] = relationship(foreign_keys=[display_unit_id])
    min_stock_unit: Mapped[Unit | None] = relationship(foreign_keys=[min_stock_unit_id])
    lots: Mapped[list[Lot]] = relationship(
        back_populates="product", cascade="all, delete-orphan"
    )


class ApiToken(Base):
    """Langlebiges Token für externe Zugriffe (z.B. Home Assistant).

    Gespeichert wird nur der SHA-256-Hash; der Klartext wird einmalig beim
    Anlegen angezeigt.
    """

    __tablename__ = "api_tokens"

    id: Mapped[int] = mapped_column(Integer, primary_key=True)
    name: Mapped[str] = mapped_column(String(120), nullable=False)
    token_hash: Mapped[str] = mapped_column(String(64), unique=True, index=True, nullable=False)
    user_id: Mapped[int | None] = mapped_column(
        ForeignKey("users.id", ondelete="CASCADE"), nullable=True
    )
    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)
    last_used_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)


class Barcode(Base):
    """Zusätzliche EAN-Codes für ein Produkt ODER eine Gruppe.

    Beispiel Gruppe "Mehl": alle Mehl-Marken einscannen; ein Scan ordnet das
    Produkt dann automatisch dieser Gruppe zu.
    """

    __tablename__ = "barcodes"

    id: Mapped[int] = mapped_column(Integer, primary_key=True)
    code: Mapped[str] = mapped_column(String(64), unique=True, index=True, nullable=False)
    # Freitext zur Einordnung, z.B. "Mehl bei Aldi"
    note: Mapped[str | None] = mapped_column(String(120), nullable=True)
    product_id: Mapped[int | None] = mapped_column(
        ForeignKey("products.id", ondelete="CASCADE"), nullable=True
    )
    group_id: Mapped[int | None] = mapped_column(
        ForeignKey("groups.id", ondelete="CASCADE"), nullable=True
    )
    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)


class Lot(Base):
    __tablename__ = "lots"

    id: Mapped[int] = mapped_column(Integer, primary_key=True)
    product_id: Mapped[int] = mapped_column(
        ForeignKey("products.id", ondelete="CASCADE"), nullable=False
    )
    quantity: Mapped[float] = mapped_column(Float, nullable=False)  # in base units
    best_before: Mapped[date | None] = mapped_column(Date, nullable=True)
    location_id: Mapped[int | None] = mapped_column(
        ForeignKey("locations.id", ondelete="SET NULL"), nullable=True
    )
    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)

    product: Mapped[Product] = relationship(back_populates="lots")


class Movement(Base):
    __tablename__ = "movements"

    id: Mapped[int] = mapped_column(Integer, primary_key=True)
    product_id: Mapped[int] = mapped_column(
        ForeignKey("products.id", ondelete="CASCADE"), nullable=False
    )
    lot_id: Mapped[int | None] = mapped_column(
        ForeignKey("lots.id", ondelete="SET NULL"), nullable=True
    )
    user_id: Mapped[int | None] = mapped_column(
        ForeignKey("users.id", ondelete="SET NULL"), nullable=True
    )
    type: Mapped[MovementType] = mapped_column(Enum(MovementType), nullable=False)
    quantity: Mapped[float] = mapped_column(Float, nullable=False)  # in base units
    unit_used: Mapped[str] = mapped_column(String(32), nullable=False)  # what user entered
    note: Mapped[str | None] = mapped_column(String(255), nullable=True)
    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)


class Setting(Base):
    __tablename__ = "settings"

    key: Mapped[str] = mapped_column(String(64), primary_key=True)
    value: Mapped[str] = mapped_column(String(255), nullable=False)