from sqlalchemy import create_engine


def create_connection():
    db_name = get_env_variable("DB_NAME")
    db_user = get_env_variable("DB_USER")
    db_password = get_env_variable("DB_PASSWORD")
    db_url = get_env_variable("DB_URL")
    db_connection_uri = "mysql+pymysql://{user}:{pw}@{url}/{db}".format(
        user=db_user, pw=db_password, url=db_url, db=db_name
    )
    engine = sqlalchemy.create_engine(db_connection_uri, echo=True)


def get_env_variable(name):
    try:
        return os.environ[name]
    except KeyError:
        message = "Expected environment variable '{}' not set.".format(name)
        raise Exception(message)