"""Follow model: a one-way relationship requiring no approval."""

from sqlalchemy import CheckConstraint, Column, DateTime, ForeignKey, Integer, UniqueConstraint
from sqlalchemy.orm import relationship
from sqlalchemy.sql import func

from app.database import Base


class Follow(Base):
    __tablename__ = "follows"
    __table_args__ = (
        UniqueConstraint(
            "follower_id",
            "followed_id",
            name="uq_follows_follower_followed",
        ),
        CheckConstraint(
            "follower_id <> followed_id",
            name="ck_follows_no_self",
        ),
    )

    id = Column(Integer, primary_key=True, index=True)
    follower_id = Column(
        Integer,
        ForeignKey("users.id", ondelete="CASCADE"),
        nullable=False,
        index=True,
    )
    followed_id = Column(
        Integer,
        ForeignKey("users.id", ondelete="CASCADE"),
        nullable=False,
        index=True,
    )
    created_at = Column(DateTime(timezone=True), server_default=func.now())

    follower = relationship(
        "User",
        foreign_keys=[follower_id],
        back_populates="follows_given",
    )
    followed = relationship(
        "User",
        foreign_keys=[followed_id],
        back_populates="followers",
    )