"""Add parent_snapshot_id and delta_blob to musehub_snapshots.

Enables tip-to-tip object diffing in wire_fetch_mpack (new_oids = want_tip -
have_tip in O(files) rather than O(commits × files)) and delta-compressed
snapshot wire format (send only the delta, not the full manifest, per commit).
"""

from __future__ import annotations

import sqlalchemy as sa
from alembic import op

revision = "0066"
down_revision = "0065"
branch_labels = None
depends_on = None


def upgrade() -> None:
    op.add_column(
        "musehub_snapshots",
        sa.Column("parent_snapshot_id", sa.String(128), nullable=True),
    )
    op.add_column(
        "musehub_snapshots",
        sa.Column("delta_blob", sa.LargeBinary, nullable=True),
    )


def downgrade() -> None:
    op.drop_column("musehub_snapshots", "delta_blob")
    op.drop_column("musehub_snapshots", "parent_snapshot_id")