"""labels: a tag's name is unique among LIVE tags only

Revision ID: 0040
Revises: 0039
Create Date: 2026-10-08

Deleting a tag now leaves a tombstone row (`purged_at` set) so the change feed can
tell linked devices about it (#5382). Before, the web deleted the row outright and
devices never heard. A tombstone must not hold its name: creating `#grocery` again
after deleting it has to make a live tag, on the web and from a device alike. So
`(owner_id, name)` stays unique only where `purged_at IS NULL`.

## Downgrade

Restores the plain unique constraint. Tombstones are deleted first, since one may
share its name with a live tag; devices that have not pulled since keep the tag.
"""
import sqlalchemy as sa
from alembic import op

revision = "0040"
down_revision = "0039"
branch_labels = None
depends_on = None


def upgrade() -> None:
    op.drop_constraint("uq_labels_owner_name", "labels", type_="unique")
    op.create_index(
        "uq_labels_owner_name_live",
        "labels",
        ["owner_id", "name"],
        unique=True,
        postgresql_where=sa.text("purged_at IS NULL"),
    )


def downgrade() -> None:
    op.drop_index("uq_labels_owner_name_live", table_name="labels")
    op.execute("DELETE FROM labels WHERE purged_at IS NOT NULL")
    op.create_unique_constraint("uq_labels_owner_name", "labels", ["owner_id", "name"])