#!/usr/bin/python
"""
Author: Vertigo Designs, Ryan Summers
        Robert Jördens

Description: Provides an API for controlling Miniconf devices over MQTT.
"""
import asyncio
import json
import logging
import uuid

from gmqtt import Client as MqttClient

LOGGER = logging.getLogger(__name__)

class MiniconfException(Exception):
    """ Generic exceptions generated by Miniconf. """


class Miniconf:
    """An asynchronous API for controlling Miniconf devices using MQTT."""

    @classmethod
    async def create(cls, prefix, broker):
        """Create a connection to the broker and a Miniconf device using it."""
        client = MqttClient(client_id='')
        await client.connect(broker)
        return cls(client, prefix)

    def __init__(self, client, prefix):
        """Constructor.

        Args:
            client: A connected MQTT5 client.
            prefix: The MQTT toptic prefix of the device to control.
        """
        self.request_id = 0
        self.client = client
        self.prefix = prefix
        self.inflight = {}
        self.client.on_message = self._handle_response
        self.response_topic = f'{prefix}/response/{uuid.uuid1().hex}'
        self.client.subscribe(self.response_topic)

    def _handle_response(self, _client, topic, payload, _qos, properties):
        """Callback function for when messages are received over MQTT.

        Args:
            _client: The MQTT client.
            topic: The topic that the message was received on.
            payload: The payload of the message.
            _qos: The quality-of-service level of the received packet
            properties: A dictionary of properties associated with the message.
        """
        if topic == self.response_topic:
            # Extract request_id corrleation data from the properties
            request_id = int.from_bytes(
                properties['correlation_data'][0], 'big')

            self.inflight[request_id].set_result(json.loads(payload))
            del self.inflight[request_id]
        else:
            LOGGER.warning('Unexpected message on "%s"', topic)

    async def command(self, path, value, retain=True):
        """Write the provided data to the specified path.

        Args:
            path: The path to write the message to.
            value: The value to write to the path.
            retain: Retain the MQTT message changing the setting
                by the broker.

        Returns:
            The response to the command as a dictionary.
        """
        topic = f'{self.prefix}/settings/{path}'

        fut = asyncio.get_running_loop().create_future()

        # Assign unique correlation data for response dispatch
        assert self.request_id not in self.inflight
        self.inflight[self.request_id] = fut
        correlation_data = self.request_id.to_bytes(4, 'big')
        self.request_id += 1

        payload = json.dumps(value)
        LOGGER.info('Sending "%s" to "%s"', value, topic)

        self.client.publish(
            topic, payload=payload, qos=0, retain=retain,
            response_topic=self.response_topic,
            correlation_data=correlation_data)

        result = await fut
        if result['code'] != 0:
            raise MiniconfException(result['msg'])