import enum
import uuid
from datetime import date, datetime
from typing import TYPE_CHECKING

from sqlalchemy import (
    CheckConstraint,
    Date,
    DateTime,
    Enum,
    ForeignKey,
    Index,
    Integer,
    String,
    Uuid,
    func,
)
from sqlalchemy.orm import Mapped, mapped_column, relationship

from app.database import Base

if TYPE_CHECKING:
    from app.models.category import Category


class TransactionType(str, enum.Enum):
    income = "income"
    expense = "expense"


class Transaction(Base):
    __tablename__ = "transactions"
    __table_args__ = (
        CheckConstraint("amount_cents > 0", name="ck_transactions_amount_positive"),
        Index("ix_transactions_user_date", "user_id", "transaction_date", "deleted_at"),
        Index("ix_transactions_user_category", "user_id", "category_id", "deleted_at"),
    )

    id: Mapped[uuid.UUID] = mapped_column(Uuid, primary_key=True, default=uuid.uuid4)
    user_id: Mapped[uuid.UUID] = mapped_column(
        Uuid, ForeignKey("users.id", ondelete="CASCADE"), nullable=False
    )
    category_id: Mapped[uuid.UUID] = mapped_column(
        Uuid, ForeignKey("categories.id"), nullable=False
    )
    amount_cents: Mapped[int] = mapped_column(Integer, nullable=False)
    type: Mapped[TransactionType] = mapped_column(
        Enum(TransactionType, name="transactiontype", native_enum=False, length=10),
        nullable=False,
    )
    description: Mapped[str | None] = mapped_column(String(255), nullable=True)
    transaction_date: Mapped[date] = mapped_column(Date, nullable=False)
    deleted_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=False), nullable=True)
    created_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=False), nullable=False, server_default=func.now()
    )
    updated_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=False), nullable=False, server_default=func.now()
    )

    # Relationships — use selectinload() explicitly; lazy="raise" prevents accidental N+1
    category: Mapped["Category"] = relationship("Category", lazy="raise")