"""plex library HU-overlay columns (E5 S5a)

Adds `metadata_lang` (default 'en') and a self-referential `overlay_of` to plex_libraries. An
OVERLAY library is the Hungarian-metadata twin of another section: it is never browsed on its own —
its titles' HU fields are written onto the matched EN rows (paired by `guid`, see 0064). Cheap:
metadata-only, no table rewrite.
"""

from typing import Sequence, Union

import sqlalchemy as sa
from alembic import op

revision: str = "0063_plex_library_overlay"
down_revision: Union[str, None] = "0062_drop_redundant_idx"
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    op.add_column(
        "plex_libraries",
        sa.Column("metadata_lang", sa.String(8), nullable=False, server_default="en"),
    )
    op.add_column(
        "plex_libraries",
        sa.Column(
            "overlay_of",
            sa.Integer(),
            sa.ForeignKey("plex_libraries.id", ondelete="SET NULL"),
            nullable=True,
        ),
    )
    op.create_index("ix_plex_libraries_overlay_of", "plex_libraries", ["overlay_of"])


def downgrade() -> None:
    op.drop_index("ix_plex_libraries_overlay_of", table_name="plex_libraries")
    op.drop_column("plex_libraries", "overlay_of")
    op.drop_column("plex_libraries", "metadata_lang")