import os
import json
import urllib.parse

import boto3

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

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

# trigger by S3 events
def lambda_handler(event, _context):
    bucket = event['Records'][0]['s3']['bucket']['name']
    key = urllib.parse.unquote_plus(event['Records'][0]['s3']['object']['key'], encoding='utf-8')

    try:
        faces = detect_faces(key, bucket)
    except Exception as e:
        print(e)
        print(f"Error while detecting faces in object {key} from bucket {bucket}.")
        raise e
    
    try:
        iot_publish({ "faces": faces })
    except Exception as e:
        print(e)
        print(f"Error while publishing to MQTT topic {TOPIC}.")
        raise e
    
    return str(faces)


def detect_faces(photo, bucket):
    response = rekognition.detect_faces(
                   Image={
                       'S3Object': {
                           'Bucket': bucket,
                           'Name': photo
                       }
                   },
                   Attributes=['ALL']
               )

    return len(response['FaceDetails'])


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