from sqlalchemy import DateTime, Integer, ForeignKey, UniqueConstraint, func
from sqlalchemy.orm import Mapped, mapped_column, relationship
from datetime import datetime
from app.database import Base


class ProjectTaskAssignment(Base):
    __tablename__ = "project_task_assignments"
    __table_args__ = (
        UniqueConstraint("task_id", "user_id", name="uq_task_assignments_task_user"),
    )

    id: Mapped[int] = mapped_column(primary_key=True, index=True)
    task_id: Mapped[int] = mapped_column(
        Integer, ForeignKey("project_tasks.id", ondelete="CASCADE"), nullable=False, index=True
    )
    user_id: Mapped[int] = mapped_column(
        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
    )
    assigned_by: Mapped[int] = mapped_column(
        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False
    )
    created_at: Mapped[datetime] = mapped_column(
        DateTime, default=func.now(), server_default=func.now()
    )

    # Relationships — lazy="raise" to prevent N+1
    task: Mapped["ProjectTask"] = relationship(back_populates="assignments", lazy="raise")
    user: Mapped["User"] = relationship(foreign_keys=[user_id], lazy="raise")
    assigner: Mapped["User"] = relationship(foreign_keys=[assigned_by], lazy="raise")