import os
import json

import boto3
from botocore.exceptions import ClientError

TOPIC = os.getenv("MQTT_TOPIC", "")
BUCKET = os.getenv("BUCKET", "")

s3 = boto3.client('s3')
iot_data = boto3.client('iot-data')

# trigger by MQTT topic events
def lambda_handler(event, _context):
    filename = event['filename']

    try:
        result = s3.generate_presigned_put(BUCKET, filename)
        print("Got presigned URL: {}".format(result['url']))
    except ClientError as e:
        print(e)
        print("Couldn't get a presigned URL")
        raise e

    try:
        iot_publish(result)
    except Exception as e:
        print(e)
        print(f"Error while publishing to MQTT topic {TOPIC}.")
        raise e
    
    return result['url']


def iot_publish(payload):
    iot_data.publish(
        topic=TOPIC,
        qos=0,
        payload=json.dumps(payload)
    )