from logging.config import fileConfig

from alembic import context
from sqlalchemy import engine_from_config, pool

# this is the Alembic Config object, which provides
# access to the values within the .ini file in use.
config = context.config

# Interpret the config file for Python logging.
# This line sets up loggers basically.
# Driven from `fluksio.core.db` there is no ini file to read logging from.
if config.config_file_name is not None:
    fileConfig(config.config_file_name)

# add your model's MetaData object here
# for 'autogenerate' support
# from myapp import mymodel
# target_metadata = mymodel.Base.metadata
# target_metadata = None

from fluksio.models import SQLModel  # noqa
from fluksio.core.config import settings  # noqa
from fluksio.core.types import UTCDateTime  # noqa

target_metadata = SQLModel.metadata


def render_item(type_, obj, autogen_context):
    """Write the decorator out as the type it wraps.

    A revision naming `UTCDateTime` would have to import from the app, which
    ties a migration to a version of it. What it stores is a timezone-aware
    timestamp, so that is what the revision says.
    """
    if type_ == "type" and isinstance(obj, UTCDateTime):
        autogen_context.imports.add("import sqlalchemy as sa")
        return "sa.DateTime(timezone=True)"
    return False


# other values from the config, defined by the needs of env.py,
# can be acquired:
# my_important_option = config.get_main_option("my_important_option")
# ... etc.


def get_url():
    return str(settings.SQLALCHEMY_DATABASE_URI)


def run_migrations_offline():
    """Run migrations in 'offline' mode.

    This configures the context with just a URL
    and not an Engine, though an Engine is acceptable
    here as well.  By skipping the Engine creation
    we don't even need a DBAPI to be available.

    Calls to context.execute() here emit the given string to the
    script output.

    """
    url = get_url()
    context.configure(
        url=url, target_metadata=target_metadata, literal_binds=True, compare_type=True
    )

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


def run_migrations_online():
    """Run migrations in 'online' mode.

    In this scenario we need to create an Engine
    and associate a connection with the context.

    """
    # `fluksio.core.db.migrate` hands us the connection it is already inside;
    # the CLI and `alembic` on the command line make their own.
    connection = config.attributes.get("connection")
    if connection is not None:
        _run(connection)
        return

    configuration = config.get_section(config.config_ini_section)
    configuration["sqlalchemy.url"] = get_url()
    connectable = engine_from_config(
        configuration,
        prefix="sqlalchemy.",
        poolclass=pool.NullPool,
    )

    with connectable.connect() as connection:
        _run(connection)


def _run(connection):
    context.configure(
        connection=connection,
        target_metadata=target_metadata,
        compare_type=True,
        render_item=render_item,
        # SQLite cannot ALTER much: batch mode rebuilds the table instead.
        render_as_batch=connection.dialect.name == "sqlite",
    )
    with context.begin_transaction():
        context.run_migrations()


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