"""Alembic migration environment.

The connection URL comes from the application settings rather than from
``alembic.ini``, so ``backend/.env`` stays the single source of truth. The URL
is passed to SQLAlchemy as a :class:`~sqlalchemy.engine.URL` object: rendering
it back to a string would re-introduce the escaping problem around the ``@``
in the TiDB password.

``target_metadata`` is wired to :class:`app.db.base.Base`, so
``alembic revision --autogenerate`` will pick up models as soon as they are
defined and imported by ``app.models``. Today that package is empty, so an
autogenerated revision is expected to contain no operations.
"""

from logging.config import fileConfig

from alembic import context
from sqlalchemy import create_engine, pool

from app.core.config import get_settings
from app.db.base import Base

# Import the models package so that every model module is registered on
# Base.metadata before autogenerate inspects it. The package defines no models
# yet; keeping the import here means the first model added is picked up with no
# further change to this file.
from app import models  # noqa: F401

config = context.config

if config.config_file_name is not None:
    fileConfig(config.config_file_name)

target_metadata = Base.metadata

settings = get_settings()


def run_migrations_offline() -> None:
    """Emit SQL to stdout without connecting to the database."""
    context.configure(
        url=settings.sqlalchemy_url,
        target_metadata=target_metadata,
        literal_binds=True,
        dialect_opts={"paramstyle": "named"},
        compare_type=True,
    )

    with context.begin_transaction():
        context.run_migrations()


def run_migrations_online() -> None:
    """Connect to TiDB and apply migrations."""
    connectable = create_engine(
        settings.sqlalchemy_url,
        poolclass=pool.NullPool,
        future=True,
    )

    with connectable.connect() as connection:
        context.configure(
            connection=connection,
            target_metadata=target_metadata,
            compare_type=True,
        )

        with context.begin_transaction():
            context.run_migrations()


if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()