"""Utils related to databases."""

import sqlite3
import sys

from sqlalchemy import event

from masters_registry import config
from masters_registry.connectors import mysql
from masters_registry.models import bulk_tasks


@event.listens_for(mysql._bulk_statuses_engine, 'connect')
def sqlite_engine_connect(dbapi_connection, connection_record):
    """Listener for the event of establishing connection to a SQLite database.

    Creates `isnull` function within SQLite engine.
    """
    if not isinstance(dbapi_connection, sqlite3.Connection):
        return

    dbapi_connection.create_function(config.ISNULL_FUNC, 1, _is_null)


def _is_null(val):
    """A substitute for missing Sqlite isnull function."""
    return 0 if val is None else 1


def create_tables():
    """Create tables for testing purposes."""
    with mysql.bulk_statuses_session_scope() as session:
        exit_if_not_test_environment(session)
    bulk_tasks.BaseModel.metadata.create_all(mysql._bulk_statuses_engine)


def drop_tables():
    """Drop track and related tables."""
    with mysql.bulk_statuses_session_scope() as session:
        exit_if_not_test_environment(session)
    bulk_tasks.BaseModel.metadata.drop_all(mysql._bulk_statuses_engine)


def exit_if_not_test_environment(session):
    """For safety, only run tests in test environment pointed to sqlite.

    Exit if not in test environment or not pointed to sqlite.
    """
    if config.ENVIRONMENT != config.TEST_ENVIRONMENT:
        sys.exit('Environment must be set to {}.'.format(
            config.TEST_ENVIRONMENT))

    if 'sqlite' not in session.bind.url.drivername:
        sys.exit('Tests must point to sqlite database.')