"""Friendship model: a one-directional request that becomes mutual on accept."""

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

from app.database import Base


class FriendshipStatus:
    """String values for the friendship.status column."""

    PENDING = "pending"
    ACCEPTED = "accepted"


class Friendship(Base):
    __tablename__ = "friendships"
    __table_args__ = (
        UniqueConstraint(
            "requester_id",
            "addressee_id",
            name="uq_friendships_pair",
        ),
        CheckConstraint(
            "requester_id <> addressee_id",
            name="ck_friendships_no_self",
        ),
        CheckConstraint(
            "status IN ('pending', 'accepted')",
            name="ck_friendships_status",
        ),
    )

    id = Column(Integer, primary_key=True, index=True)
    requester_id = Column(
        Integer,
        ForeignKey("users.id", ondelete="CASCADE"),
        nullable=False,
        index=True,
    )
    addressee_id = Column(
        Integer,
        ForeignKey("users.id", ondelete="CASCADE"),
        nullable=False,
        index=True,
    )
    status = Column(
        String(20),
        nullable=False,
        default=FriendshipStatus.PENDING,
        server_default=FriendshipStatus.PENDING,
    )
    created_at = Column(DateTime(timezone=True), server_default=func.now())
    updated_at = Column(DateTime(timezone=True), onupdate=func.now())

    requester = relationship(
        "User",
        foreign_keys=[requester_id],
        back_populates="sent_friend_requests",
    )
    addressee = relationship(
        "User",
        foreign_keys=[addressee_id],
        back_populates="received_friend_requests",
    )