#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
# SPDX-License-Identifier: Apache-2.0
import cfnresponse
import uuid
import logging
import os
import sys
import boto3
import botocore

logger = logging.getLogger(__name__)
log_level = getattr(logging, str(os.getenv('LOG_LEVEL', 'INFO')))
logging.basicConfig(stream=sys.stdout, format='%(levelname)s: %(message)s', level=log_level)
boto_config = botocore.config.Config(user_agent_extra=os.getenv('USER_AGENT_STRING'))
cfn_client = boto3.client('cloudformation', config=boto_config)


def lambda_handler(event, context):
    # Returns UUID for metrics.
    # Generates new UUID for new deployment and retrieves existing UUID for an update event.

    try:
        logger.info(event)
        logger.info(context)
        request = event.get('RequestType')
        response_data = {'UUID': ''}
        if request == 'Create':
            uuid_value = generate_new_uuid()
            response_data = {'UUID': uuid_value}
        elif request == 'Update':
            uuid_value = get_uuid_for_update_event(event)
            response_data = {'UUID': uuid_value}
        logger.info(response_data)
        cfnresponse.send(event, context, 'SUCCESS', response_data)
    except Exception as e:
        logger.error(f'Exception: {e}')
        cfnresponse.send(event, context, 'FAILED', {}, context.log_stream_name)


def get_uuid_for_update_event(event):
    existing_uuid = get_existing_uuid_from_current_stack(event)
    if existing_uuid == '':
        uuid_value = generate_new_uuid()
    else:
        uuid_value = existing_uuid
    return uuid_value


def get_existing_uuid_from_current_stack(event):
    response = describe_existing_stack(event)
    existing_uuid = ''
    if response.get('Stacks'):
        output_list = response.get('Stacks')[0].get('Outputs')
        logger.info(output_list)
        for item in output_list:
            if item.get('OutputKey') == 'UUID':
                existing_uuid = item.get('OutputValue')
    return existing_uuid


def describe_existing_stack(event):
    response = {}
    try:
        response = cfn_client.describe_stacks(StackName=event['StackId'])
    except Exception as e:
        logger.error(f'Error occurred when calling the describe stack operation {e}')

    logger.info(f'Response for describe stack is {response}')
    return response


def generate_new_uuid():
    return str(uuid.uuid4())