import uuid

from sqlalchemy import ForeignKey, Text, UniqueConstraint
from sqlalchemy.dialects.postgresql import UUID
from sqlalchemy.orm import Mapped, mapped_column, relationship

from api.models.base import Base, TimestampMixin, new_uuid


class WorkstreamDependency(Base, TimestampMixin):
    """Directed dependency edge: `from_workstream` depends on `to_workstream`.

    Semantics: `to_workstream` must reach a satisfactory state before
    `from_workstream` can fully proceed.  Hard deletes are intentional —
    removing an edge removes a constraint, not information.
    """

    __tablename__ = "workstream_dependencies"
    __table_args__ = (
        UniqueConstraint("from_workstream_id", "to_workstream_id", name="uq_ws_dep_pair"),
    )

    id: Mapped[uuid.UUID] = mapped_column(
        UUID(as_uuid=True), primary_key=True, default=new_uuid
    )
    from_workstream_id: Mapped[uuid.UUID] = mapped_column(
        UUID(as_uuid=True),
        ForeignKey("workstreams.id", ondelete="CASCADE"),
        nullable=False,
        index=True,
    )
    to_workstream_id: Mapped[uuid.UUID] = mapped_column(
        UUID(as_uuid=True),
        ForeignKey("workstreams.id", ondelete="CASCADE"),
        nullable=False,
        index=True,
    )
    description: Mapped[str | None] = mapped_column(Text, nullable=True)

    from_workstream: Mapped["Workstream"] = relationship(  # noqa: F821
        "Workstream", foreign_keys=[from_workstream_id]
    )
    to_workstream: Mapped["Workstream"] = relationship(  # noqa: F821
        "Workstream", foreign_keys=[to_workstream_id]
    )