# Taken initially from https://aws.amazon.com/premiumsupport/knowledge-center/attach-second-eni-auto-scaling/
# This code is intended as an example for a blog post by Alex Addison / Lexis Nexis
# In order to use it, you will need to replace the interface ID (marked #TODO)

import boto3
import botocore
from datetime import datetime

ec2_client = boto3.client('ec2')
asg_client = boto3.client('autoscaling')


def lambda_handler(event, context):
    if event["detail-type"] == "EC2 Instance-launch Lifecycle Action":
        instance_id = event['detail']['EC2InstanceId']
        LifecycleHookName=event['detail']['LifecycleHookName']
        AutoScalingGroupName=event['detail']['AutoScalingGroupName']
        subnet_id = get_subnet_id(instance_id)
        interface_id = "eni-0123456789abcdef" #TODO specify or find interface
        attachment = attach_interface(interface_id, instance_id)
        if not interface_id or not attachment:
            complete_lifecycle_action_failure(LifecycleHookName,AutoScalingGroupName,instance_id)
        else:
            complete_lifecycle_action_success(LifecycleHookName,AutoScalingGroupName,instance_id)
       
        
def get_subnet_id(instance_id):
    try:
        result = ec2_client.describe_instances(InstanceIds=[instance_id])
        vpc_subnet_id = result['Reservations'][0]['Instances'][0]['SubnetId']
        log("Subnet id: {}".format(vpc_subnet_id))

    except botocore.exceptions.ClientError as e:
        log("Error describing the instance {}: {}".format(instance_id, e.response['Error']))
        vpc_subnet_id = None

    return vpc_subnet_id

def attach_interface(network_interface_id, instance_id):
    attachment = None

    if network_interface_id and instance_id:
        try:
            attach_interface = ec2_client.attach_network_interface(
                NetworkInterfaceId=network_interface_id,
                InstanceId=instance_id,
                DeviceIndex=1
            )
            attachment = attach_interface['AttachmentId']
            log("Created network attachment: {}".format(attachment))
        except botocore.exceptions.ClientError as e:
            log("Error attaching network interface: {}".format(e.response['Error']))

    return attachment

def complete_lifecycle_action_success(hookname,groupname,instance_id):
    try:
        asg_client.complete_lifecycle_action(
                LifecycleHookName=hookname,
                AutoScalingGroupName=groupname,
                InstanceId=instance_id,
                LifecycleActionResult='CONTINUE'
            )
        log("Lifecycle hook CONTINUEd for: {}".format(instance_id))
    except botocore.exceptions.ClientError as e:
            log("Error completing life cycle hook for instance {}: {}".format(instance_id, e.response['Error']))
            log('{"Error": "1"}')    
            
def complete_lifecycle_action_failure(hookname,groupname,instance_id):
    try:
        asg_client.complete_lifecycle_action(
                LifecycleHookName=hookname,
                AutoScalingGroupName=groupname,
                InstanceId=instance_id,
                LifecycleActionResult='ABANDON'
            )
        log("Lifecycle hook ABANDONed for: {}".format(instance_id))
    except botocore.exceptions.ClientError as e:
            log("Error completing life cycle hook for instance {}: {}".format(instance_id, e.response['Error']))
            log('{"Error": "1"}')    
    

def log(error):
    print('{}Z {}'.format(datetime.utcnow().isoformat(), error))