"""users：language_preference 字段

Revision ID: 0018_users_language_preference
Revises: 0017_segment_narrative_defer
"""

from typing import Sequence, Union

import sqlalchemy as sa

from alembic import op

revision: str = "0018_users_language_preference"
down_revision: Union[str, None] = "0017_segment_narrative_defer"
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def _column_names(table_name: str) -> set[str]:
    bind = op.get_bind()
    inspector = sa.inspect(bind)
    return {column["name"] for column in inspector.get_columns(table_name)}


def upgrade() -> None:
    columns = _column_names("users")
    if "language_preference" not in columns:
        op.add_column(
            "users",
            sa.Column(
                "language_preference",
                sa.String(length=8),
                nullable=False,
                server_default=sa.text("'zh'"),
            ),
        )


def downgrade() -> None:
    columns = _column_names("users")
    if "language_preference" in columns:
        op.drop_column("users", "language_preference")