"""
Offer MQTT listening automation rules.

For more details about this automation rule, please refer to the documentation
at https://home-assistant.io/docs/automation/trigger/#mqtt-trigger
"""
import asyncio
import json

import voluptuous as vol

from homeassistant.core import callback
from homeassistant.components import mqtt
from homeassistant.const import CONF_PLATFORM, CONF_PAYLOAD
import homeassistant.helpers.config_validation as cv

DEPENDENCIES = ["mqtt"]

CONF_TOPIC = "topic"

TRIGGER_SCHEMA = vol.Schema(
    {
        vol.Required(CONF_PLATFORM): mqtt.DOMAIN,
        vol.Required(CONF_TOPIC): mqtt.valid_subscribe_topic,
        vol.Optional(CONF_PAYLOAD): cv.string,
    }
)


@asyncio.coroutine
def async_trigger(hass, config, action):
    """Listen for state changes based on configuration."""
    topic = config.get(CONF_TOPIC)
    payload = config.get(CONF_PAYLOAD)

    @callback
    def mqtt_automation_listener(msg_topic, msg_payload, qos):
        """Listen for MQTT messages."""
        if payload is None or payload == msg_payload:
            data = {
                "platform": "mqtt",
                "topic": msg_topic,
                "payload": msg_payload,
                "qos": qos,
            }

            try:
                data["payload_json"] = json.loads(msg_payload)
            except ValueError:
                pass

            hass.async_run_job(action, {"trigger": data})

    remove = yield from mqtt.async_subscribe(hass, topic, mqtt_automation_listener)
    return remove