# -*- coding: utf-8 -*-
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals

from builtins import object
import logging
import os
import random

from airflow import settings
from airflow.models import Connection
from airflow.exceptions import AirflowException

CONN_ENV_PREFIX = 'AIRFLOW_CONN_'


class BaseHook(object):
    """
    Abstract base class for hooks, hooks are meant as an interface to
    interact with external systems. MySqlHook, HiveHook, PigHook return
    object that can handle the connection and interaction to specific
    instances of these systems, and expose consistent methods to interact
    with them.
    """
    def __init__(self, source):
        pass

    @classmethod
    def get_connections(cls, conn_id):
        session = settings.Session()
        db = (
            session.query(Connection)
            .filter(Connection.conn_id == conn_id)
            .all()
        )
        session.expunge_all()
        session.close()
        if not db:
            raise AirflowException(
                "The conn_id `{0}` isn't defined".format(conn_id))
        return db

    @classmethod
    def get_connection(cls, conn_id):
        environment_uri = os.environ.get(CONN_ENV_PREFIX + conn_id.upper())
        conn = None
        if environment_uri:
            conn = Connection(conn_id=conn_id, uri=environment_uri)
        else:
            conn = random.choice(cls.get_connections(conn_id))
        if conn.host:
            logging.info("Using connection to: " + conn.host)
        return conn

    @classmethod
    def get_hook(cls, conn_id):
        connection = cls.get_connection(conn_id)
        return connection.get_hook()

    def get_conn(self):
        raise NotImplementedError()

    def get_records(self, sql):
        raise NotImplementedError()

    def get_pandas_df(self, sql):
        raise NotImplementedError()

    def run(self, sql):
        raise NotImplementedError()
