"""DNS Lambda function module."""

import os

import boto3

# Set variables
STACK_NAME = os.environ['stack_name']
DOMAIN_NAME = os.environ['domain_name']
ZONE_ID = os.environ['zone_id']
TTL_SECONDS = os.environ.get('ttl_seconds', 300)


def handler(event, context):
    """Lambda entry point."""
    route53 = boto3.client('route53')
    compute = boto3.client('ec2')
    autoscaling = boto3.client('autoscaling')
    print(
        'Autoscaling Group: "' + event['detail']['AutoScalingGroupName'] + '"')
    print('Autoscaling Event: "' + event['detail-type'] + '"')

    # Run if we're processing a launch or terminate event:
    if (event['detail-type'] == 'EC2 Instance Launch Successful') or (
            event['detail-type'] == 'EC2 Instance Terminate Successful'):
        print(
            'Handling ' + event['detail-type'] + ' Event for ' +
            event['detail']['AutoScalingGroupName'])

        # Get details about the autoscaling-group:
        print('Retrieving ASG details ...')

        # Look up the autoscaling group:
        try:
            auto_scaling_group = autoscaling.describe_auto_scaling_groups(
                AutoScalingGroupNames=[
                    event['detail']['AutoScalingGroupName'],
                ],
                MaxRecords=1
            )
        except Exception as e:
            print('Unable to find ASG:', e)
            print('Auto scaling group name: {}'.format(
                event['detail']['AutoScalingGroupName']))
            raise e

        route53_meta = {}
        route53_meta['stackName'] = STACK_NAME
        print('Stack Name: "' + route53_meta['stackName'] + '"')

        route53_meta['domainName'] = DOMAIN_NAME
        print('Domain Name: "' + route53_meta['domainName'] + '"')

        route53_meta['zoneId'] = ZONE_ID
        print('R53 Zone ID: "' + route53_meta['zoneId'] + '"')

        # Build a list of running instances:
        print('Finding running instances ...')
        instance_ids = []

        # Find instances which are running:
        print(auto_scaling_group)
        for group in auto_scaling_group['AutoScalingGroups']:
            for instance in group['Instances']:
                if instance['LifecycleState'] == 'InService':
                    instance_ids.append(instance['InstanceId'])

        # Make sure we found some running instances:
        instance_len = len(instance_ids)
        if instance_len == 0:
            print('No running instances were found!')
            raise SystemExit
        else:
            print('Running instances: ')
            print(instance_ids)

        # Retrieve instance metadata:
        print('Getting instance metadata ...')

        # Describe the instances for this autoscaling group:
        ec2_meta = compute.describe_instances(
            DryRun=False,
            InstanceIds=instance_ids
        )

        # Build DNS address-mappings:
        print('Building address-mappings for DNS records ...')
        address_mappings = {}
        region_wide_name = (
            route53_meta['stackName'] + '.' + route53_meta['domainName'])
        print('Region wide name: ' + region_wide_name)
        address_mappings[region_wide_name] = []
        print(ec2_meta)
        for reservation in ec2_meta['Reservations']:
            private_ip = reservation['Instances'][0]['PrivateIpAddress']
            address_mappings[region_wide_name].append({'Value': private_ip})
        print(address_mappings)

        # Create DNS records in Route53:
        print('Creating DNS records ...')

        change_resource_record_sets_request = {
            'Changes': []
        }

        # Iterate through all of the record-names in addressMappings:
        for record_name, record_value in address_mappings.items():

            # Add a change to the changeBatch:
            change_resource_record_sets_request['Changes'].append(
                {
                    'Action': 'UPSERT',
                    'ResourceRecordSet': {
                        'Name': record_name,
                        'Type': 'A',
                        'TTL': TTL_SECONDS,
                        'ResourceRecords': record_value
                    }
                }
            )
        print(change_resource_record_sets_request)

        # Submit the changeResourceRecordSets() request to Route53:
        try:
            route53.change_resource_record_sets(
                HostedZoneId=route53_meta['zoneId'],
                ChangeBatch=change_resource_record_sets_request
            )
            print('DNS has been updated for an autoscaling event')
        except Exception as e:
            print('Unable to update DNS for an autoscaling event:', e)
    else:
        print('Unsupported ASG event: "' + event['detail-type'] + '"')
    print('Finished')