from __future__ import with_statement
from alembic import context
from sqlalchemy import engine_from_config, pool
import sqlalchemy.exc
from positronics_agent.v1_0.cache.schema_builder import SimpleSchemaBuilder
from positronics_agent.v1_0.cache.dialects import MySqlDialect
from positronics_agent.v1_0.models.mapper.schemas import cache
# from logging.config import fileConfig

# 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.
# fileConfig(config.config_file_name)

# add your model's MetaData object here
# for 'autogenerate' support
builder = SimpleSchemaBuilder(MySqlDialect)
try:
    builder.build_schema(cache)
except sqlalchemy.exc.ArgumentError as e:
    if "already has a primary mapper defined" not in e.message:
        raise
    # A running agent will already have a built schema
target_metadata = cache.metadata

# 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 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 = config.get_main_option("sqlalchemy.url")
    context.configure(
        url=url,
        target_metadata=target_metadata,
        literal_binds=True,
        render_as_batch=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.

    """
    connectable = config.attributes.get('engine', None)

    if connectable is None:
        connectable = engine_from_config(
            config.get_section(config.config_ini_section),
            prefix='sqlalchemy.',
            poolclass=pool.NullPool)

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

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

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