from typing import Union, Callable

import mysql.connector
import trino.dbapi
from trino.auth import BasicAuthentication
from trino.dbapi import connect
from sshtunnel import SSHTunnelForwarder


def singleton(class_):
    instances = {}

    def getinstance(*args, **kwargs):
        if class_ not in instances:
            instances[class_] = class_(*args, **kwargs)
        return instances[class_]

    return getinstance


@singleton
class MySSHTunnel:
    def __init__(
        self, ssh_host, ssh_port, ssh_username, ssh_pkey, remote_host, remote_port
    ):

        self.tunnel = SSHTunnelForwarder(
            ssh_host=(ssh_host, ssh_port),
            ssh_username=ssh_username,
            ssh_pkey=ssh_pkey,
            remote_bind_address=(remote_host, remote_port),
            local_bind_address=("127.0.0.1", remote_port),
        )

    def start(self):
        self.tunnel.start()

    def stop(self):
        self.tunnel.stop()


def get_connection(connection_config: dict) -> Union[trino.dbapi.Connection]:
    """
    Pick the right way to build a connection and pass it the connection details.

    :param connection_config: confi
    :return:
    """
    connection_builder = pick_connection_builder(connection_config["engine"])
    connection = connection_builder(connection_config)
    return connection


def get_possible_connection_builders() -> dict:
    """
    Get the complete list of connection builders.

    :return: a dict where the keys are the strings that identify each
    connection engine and the values are the callable function that will return
    a valid connection object.
    """
    return {
        "trino": get_connection_to_trino,
        "mysql": get_connection_to_mysql,
    }


def pick_connection_builder(connection_engine_name: str) -> Callable:
    """
    Get a connection builder from a string name.

    :param connection_engine_name: the string defining the connection engine.
    :return: the connection builder function.
    """
    possible_connection_builders = get_possible_connection_builders()

    try:
        connection_builder = possible_connection_builders[connection_engine_name]
    except KeyError:
        raise ValueError(
            f"Connection type {connection_engine_name} is unknown. Please review config."
        )

    return connection_builder


def get_connection_to_trino(connection_config: dict) -> trino.dbapi.Connection:
    """
    Build a connection to Trino from the passed config.

    :param connection_config: specifies host, port, etc.
    :return: the connection object
    """

    return connect(
        host=connection_config["host"],
        port=connection_config["port"],
        user=connection_config["user"],
        auth=BasicAuthentication(
            connection_config["user"],
            connection_config["password"],
        ),
        http_scheme=connection_config["http_scheme"],
        catalog=connection_config["catalog"],
        schema=connection_config["schema"],
    )


def get_connection_to_mysql(
    connection_config,
) -> mysql.connector.connection.MySQLConnection:
    """
    Build a connection to MySQL from the passed config.

    :param connection_config: specifies host, port, etc.
    :return: the connection object
    """
    connection = mysql.connector.connect(
        host=connection_config["host"],
        port=connection_config["port"],
        user=connection_config["user"],
        password=connection_config["password"],
        database=connection_config["schema"],
    )

    return connection


def clean_up_connection(connection_config: dict) -> None:
    """
    Perform any necessary connection clean up steps after the measuring session.

    :param connection_config: the connection details.
    :return: none.
    """
    if connection_config["ssh_tunneling"]["use_tunnel"]:
        close_ssh_tunnel()


def open_ssh_tunnel(connection_config: dict) -> None:
    """
    Start an SSH tunnel with the passed details.

    :param connection_config: the connection details.
    :return: none.
    """

    print(
        f"""Opening up an SSH tunnel to {connection_config["ssh_tunneling"]["ssh_host"]}"""
    )
    MySSHTunnel(
        ssh_host=connection_config["ssh_tunneling"]["ssh_host"],
        ssh_port=connection_config["ssh_tunneling"]["ssh_port"],
        ssh_username=connection_config["ssh_tunneling"]["ssh_username"],
        ssh_pkey=connection_config["ssh_tunneling"]["path_to_key"],
        remote_host=connection_config["host"],
        remote_port=connection_config["port"],
    ).start()
    print("SSH tunnel is now open.")


def close_ssh_tunnel():
    """
    Close the SSH tunnel. No details required because a singleton is being used.

    :return: None
    """
    print(f"Closing down the SSH tunnel...")
    MySSHTunnel().stop()
    print("SSH tunnel is now closed.")