import boto3

def provideHelp(params):
    message =  "Set the subject of the email to one of the following\n"
    message += "help - provides this help\n"
    message += "status - provides the status of all ec2 instances in the region\n"
    message += "start {instance-id} - starts the ec2 instance with with the specified instance-id\n"
    message += "stop {instance-id} - stops the ec2 instance with the specified instance id"

    return message

def getStatus(params):
    #get a list of all ec2 instances
    print("getStatus:Params:",params)

    #if a parameter is provided, it is the aws region to check
    if (len(params) >= 1):
        ec2 = boto3.client("ec2", params[0])
    else:
        ec2 = boto3.client("ec2")

    response = ec2.describe_instances()
    instances = response['Reservations']

    number_instances = len(instances)
    print("NumInstances:",number_instances)

    message = ""

    for instance in instances:
        print("Instance:",str(instance))
        instance_id = instance['Instances'][0]['InstanceId']

        message += instance_id + "\t"

        try:
            if (instance['Instances'][0]['Tags'][0]['Key'] == 'Name'):
                instance_name = instance['Instances'][0]['Tags'][0]['Value']

                if (instance_name == ""):
                    message += "[No Name Found]\t"
                else:
                    message += instance_name + "\t"
        except:
            message += "[No Name Found]\t"

        instance_state = instance['Instances'][0]['State']['Name']

        message += instance_state + "\t"

        try:
            instance_privateip = instance['Instances'][0]['PrivateIpAddress']
            message += instance_privateip + "\t"
        except:
            message += "[No Private IP]\t"

        try:
            instance_publicip = instance['Instances'][0]['PublicIpAddress']
            message += instance_publicip + "\t"
        except:
            message += "[No Public IP]\t"

        message += "\n"

    return message

def startInstance(params):

    if (len(params) > 1):
        instanceId = params[0]
        aws_region = params[1]
        ec2 = boto3.client("ec2", aws_region)
    else:
        instanceId = params[0]
        ec2 = boto3.client("ec2")

    try:
        response = ec2.start_instances(
            InstanceIds=[instanceId]
        )
        message = "Starting instance " + str(instanceId) + " Please check status in a couple of minutes\n" + str(response)

    except Exception as e:
        message = "Error starting instance(s) :" + str(instanceId) + " " + str(e)
        print(message)

    return message

def stopInstance(params):

    if (len(params) > 1):
        instanceId = params[0]
        aws_region = params[1]
        ec2 = boto3.client("ec2", aws_region)
    else:
        instanceId = params[0]
        ec2 = boto3.client("ec2")

    try:
        response = ec2.stop_instances(
            InstanceIds=[instanceId]
        )
        message = "Stopping instance " + str(instanceId) + " Please check status in a couple of minutes\n" + str(response)

    except Exception as e:
        message = "Error stopping instance(s) " + str(instanceId) + " " + str(e)
        print(message)
    return message

def sendEmail(fromAddress,recipientAddress,subject,body):
    #sending email
    print("sending email")

    client = boto3.client('ses')
    response = client.send_email(
        Destination={
            'ToAddresses': [recipientAddress],
        },
        Message={
            'Body': {
                'Text': {
                    'Charset': 'UTF-8',
                    'Data': body
                },
            },
            'Subject': {
                'Charset':  'UTF-8',
                'Data': subject
            },
        },
        ReplyToAddresses=[fromAddress],
        ReturnPath=fromAddress,
        Source=fromAddress
    )
    print("Response from SES:",response)

def lambda_handler(event, context):
    approvedSenders = ['john@example.com','tom@example.com','jane@example']

    print("Event:",event)
    print("Context",context)
    emailSender = event["Records"][0]["ses"]["mail"]["source"]
    emailSubject = event["Records"][0]["ses"]["mail"]["commonHeaders"]["subject"]
    command_split = emailSubject.split(" ")
    command = command_split[0].lower()

    if (len(command_split) > 1):
        commandParams = command_split[1:len(command_split)]
    else:
        commandParams = "" #if there are no command params, then just set it to blank

    print("From:",emailSender)
    print("Subject:",emailSubject)
    print("Command:",command)

    #authenticate the sender based on fromAddress
    if emailSender in approvedSenders:
        switcher = {
            "help": provideHelp,
            "status": getStatus,
            "start": startInstance,
            "stop": stopInstance
        }

        #get the command that was specified in the email
        functionToRun = switcher.get(command, lambda params: "invalid command")

        body = functionToRun(commandParams)

        sendEmail("admin@managedinstances.com",emailSender,"Execution result for command:"+ emailSubject, str(body))
    else:
        print("Sender ",emailSender," not approved for executing commands. Ignore")