from datetime import UTC, datetime

from app import db


class CardLabel(db.Model):
    """Many-to-many relationship between cards and labels"""

    __tablename__ = "card_labels"

    id = db.Column(db.Integer, primary_key=True)
    card_id = db.Column(db.Integer, db.ForeignKey("cards.id", ondelete="CASCADE"), nullable=False, index=True)
    label_id = db.Column(db.Integer, db.ForeignKey("labels.id", ondelete="CASCADE"), nullable=False, index=True)

    # Timestamps
    created_at = db.Column(db.DateTime, default=lambda: datetime.now(UTC))

    # Unique constraint to prevent duplicate associations
    __table_args__ = (db.UniqueConstraint("card_id", "label_id", name="_card_label_uc"),)

    def to_dict(self):
        """Convert card label to dictionary"""
        return {
            "id": self.id,
            "card_id": self.card_id,
            "label_id": self.label_id,
            "created_at": self.created_at.isoformat() if self.created_at else None,
        }

    def __repr__(self):
        return f"<CardLabel card_id={self.card_id} label_id={self.label_id}>"