# Copyright 2019 Google LLC
#
# 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.

"""Python Library for connecting to Google Cloud IoT Core via MQTT, using JWT.
"""

import argparse
import configparser
import datetime
import json
import jwt
import logging
import os
import paho.mqtt.client as mqtt
import threading
import time

from coral.cloudiot.ecc608 import ecc608_jwt_with_hw_alg

logger = logging.getLogger(__name__)


class CloudIot:
    """
    Manages a connection to Google Cloud IoT Core via MQTT, using a JWT for device
    authentication.

    You must configure a connection by specifying a Clout IoT configuration file (.ini). Then
    you can use :meth:`publish_message` to send an arbitrary message to your cloud project.
    """
    def __init__(self, config_file, config_section='DEFAULT'):
        """
        Args:
            config_file (str): Path to your Cloud IoT configuration file (.ini).
            config_section (str): The section name in the .ini file where the Cloud IoT Core config
                can be read. By default, it reads from the "[DEFAULT]" section.
        """
        self._config = configparser.ConfigParser()
        self._config.read(config_file)

        if not self._config.getboolean(config_section, 'Enabled'):
            logger.warn('Cloud IoT is disabled per configuration.')
            self._enabled = False
            return

        config = self._config[config_section]
        self._project_id = config['ProjectID']
        self._cloud_region = config['CloudRegion']
        self._registry_id = config['RegistryID']
        self._device_id = config['DeviceID']
        self._ca_certs = config['CACerts']
        self._message_type = config['MessageType']
        self._mqtt_bridge_hostname = config['MQTTBridgeHostName']
        self._mqtt_bridge_port = config.getint('MQTTBridgePort')

        self._mutex = threading.Lock()

        if ecc608_jwt_with_hw_alg:
            # For the HW Crypto chip, use ES256. No key is needed.
            self._algorithm = 'ES256'
            self._private_key = None
            self._jwt_inst = ecc608_jwt_with_hw_alg
        else:
            # For SW, use RS256 on a key file provided in the configuration.
            self._algorithm = 'RS256'
            rsa_cert = config['RSACertFile']
            with open(rsa_cert, 'r') as f:
                self._private_key = f.read()
            self._jwt_inst = jwt.PyJWT()

        # Create our MQTT client. The client_id is a unique string that identifies
        # this device. For Google Cloud IoT Core, it must be in the format below.
        self._client = mqtt.Client(
            client_id='projects/%s/locations/%s/registries/%s/devices/%s' %
            (self._project_id,
             self._cloud_region,
             self._registry_id,
             self._device_id))

        # With Google Cloud IoT Core, the username field is ignored, and the
        # password field is used to transmit a JWT to authorize the device.
        self._client.username_pw_set(
            username='unused', password=self._create_jwt())

        # Start thread to create new token before timeout.
        self._term_event = threading.Event()
        self._token_thread = threading.Thread(
            target=self._token_update_loop, args=(self._term_event,))
        self._token_thread.start()

        # Enable SSL/TLS support.
        self._client.tls_set(ca_certs=self._ca_certs)

        # Connect to the Google MQTT bridge.
        self._client.connect(self._mqtt_bridge_hostname,
                             self._mqtt_bridge_port)

        logger.info('Successfully connected to Cloud IoT')
        self._enabled = True

    def __enter__(self):
        return self

    def __exit__(self, exception_type, exception_value, traceback):
        if self._enabled:
            # Terminate token thread.
            self._term_event.set()
            self._token_thread.join()

    def enabled(self):
        """
        Checks whether or not Clout Iot Core is enabled, as per the config file's "Enabled" boolean.

        Returns:
            True if Cloud Iot Core is enabled, False if it's disabled.
        """
        return self._enabled

    def publish_message(self, message):
        """
        Sends an arbitrary message to the Cloud Iot Core service.

        Args:
            message (obj): The message to send. It can be any message that's serializable into a
                JSON message using :func:`json.dumps` (such as a dictionary or string).
        """
        if not self._enabled:
            return

        with self._mutex:
            # Start the network loop.
            self._client.loop_start()

            # Publish to the events or state topic based on the flag.
            sub_topic = 'events' if self._message_type == 'event' else 'state'

            mqtt_topic = '/devices/%s/%s' % (self._device_id, sub_topic)

            # Publish payload using JSON dumps to create bytes representation.
            payload = json.dumps(message)

            # Publish payload to the MQTT topic. qos=1 means at least once
            # delivery. Cloud IoT Core also supports qos=0 for at most once
            # delivery.
            self._client.publish(mqtt_topic, payload, qos=1)

            # End the network loop and finish.
            self._client.loop_stop()

    def register_message_callbacks(self, callbacks):
        """
        Specifies functions to call upon various MQTT pub-sub messages.

        Args:
            callbacks (dict): A mapping of callback names from `paho.mqtt.client callbacks
                <https://pypi.org/project/paho-mqtt/#callbacks>`_ to your own function names.
        """
        if 'on_connect' in callbacks:
            self._client.on_connect = callbacks['on_connect']
        if 'on_disconnect' in callbacks:
            self._client.on_disconnect = callbacks['on_disconnect']
        if 'on_publish' in callbacks:
            self._client.on_publish = callbacks['on_publish']
        if 'on_message' in callbacks:
            self._client.on_message = callbacks['on_message']
        if 'on_unsubscribe' in callbacks:
            self._client.on_unsubscribe = callbacks['on_unsubscribe']
        if 'on_log' in callbacks:
            self._client.on_log = callbacks['on_log']

    def _token_update_loop(self, term_event):
        # Update token every 50 minutes (of allowed 60).
        while not term_event.wait(50 * 60):
            with self._mutex:
                self._client.disconnect()

                # Set new token.
                self._client.username_pw_set(
                    username='unused', password=self._create_jwt())

                # Connect to the Google MQTT bridge.
                self._client.connect(
                    self._mqtt_bridge_hostname, self._mqtt_bridge_port)

                logger.info(
                    'Successfully re-established connection with new token')

    def _create_jwt(self):
        """Creates a JWT (https://jwt.io) to establish an MQTT connection.
            Args:
                Project_id: The cloud project ID this device belongs to
                 algorithm: The encryption algorithm to use. Either 'RS256' or 'ES256'
            Returns:
                An MQTT generated from the given project_id and private key, which
                expires in 20 minutes. After 20 minutes, your client will be
                disconnected, and a new JWT will have to be generated.
        """

        token = {
            # The time that the token was issued at
            'iat': datetime.datetime.utcnow(),
            # The time the token expires.
            'exp': datetime.datetime.utcnow() + datetime.timedelta(minutes=60),
            # The audience field should always be set to the GCP project id.
            'aud': self._project_id
        }

        return self._jwt_inst.encode(token, self._private_key, algorithm=self._algorithm)