from django.db.backends.base.base import BaseDatabaseWrapper
from django.db import connections
import cx_Oracle

__all__ = (
    'get_etl_cursor',
)


class CursorProxy(object):
    """
    A cursor proxy that allows petl to work properly with Oracle
    """

    def __init__(self, cursor):
        self._cursor = cursor

    def __iter__(self):
        return iter(self._cursor)

    def executemany(self, statement, parameters, **kwargs):
        parameters = list(parameters)
        return self._cursor.executemany(statement, parameters, **kwargs)

    def __getattr__(self, item):
        return getattr(self._cursor, item)


def get_etl_cursor(alias='default'):
    """
    Wraps the creation of a cursor to make sure that cursor is proxied,
    and unwrapped.

    :param connection: DBO object
    :return: a cursor on the underlying database
    """
    def get_connection_cursor():
        connection = connections[alias]
        if isinstance(connection, BaseDatabaseWrapper):
            if connection.connection is None:
                connection.connect()
            connection = connection.connection
        cursor = connection.cursor()
        if isinstance(cursor, cx_Oracle.Cursor):
            cursor = CursorProxy(cursor)
        return cursor
    return get_connection_cursor