import uuid

from sqlalchemy import CheckConstraint, ForeignKey, Index, String, Text, text
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 a workstream or task.

    Semantics: the target 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__ = (
        CheckConstraint(
            "(to_workstream_id IS NOT NULL AND to_task_id IS NULL) "
            "OR (to_workstream_id IS NULL AND to_task_id IS NOT NULL)",
            name="ck_ws_dep_exactly_one_target",
        ),
        Index(
            "uq_ws_dep_workstream_target",
            "from_workstream_id",
            "to_workstream_id",
            "relationship_type",
            unique=True,
            postgresql_where=text("to_workstream_id IS NOT NULL"),
        ),
        Index(
            "uq_ws_dep_task_target",
            "from_workstream_id",
            "to_task_id",
            "relationship_type",
            unique=True,
            postgresql_where=text("to_task_id IS NOT NULL"),
        ),
    )

    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 | None] = mapped_column(
        UUID(as_uuid=True),
        ForeignKey("workstreams.id", ondelete="CASCADE"),
        nullable=True,
        index=True,
    )
    to_task_id: Mapped[uuid.UUID | None] = mapped_column(
        UUID(as_uuid=True),
        ForeignKey("tasks.id", ondelete="CASCADE"),
        nullable=True,
        index=True,
    )
    relationship_type: Mapped[str] = mapped_column(
        String(40), nullable=False, default="blocks", server_default="blocks", 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 | None"] = relationship(  # noqa: F821
        "Workstream", foreign_keys=[to_workstream_id]
    )
    to_task: Mapped["Task | None"] = relationship("Task", foreign_keys=[to_task_id])  # noqa: F821