# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   autoscaling_group_elb_healthcheck_required_check
# 
# Description:
#   This control checks whether your Amazon EC2 Auto Scaling groups that are associated with a load balancer are using Elastic Load Balancing health checks.
# 
# Reports on:
#   AWS::AutoScaling::AutoScalingGroup
# 
# Evaluates:
#   AWS CloudFormation, AWS CloudFormation hook
# 
# Rule Parameters:
#   None
# 
# Scenarios:
#   Scenario: 1
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document does not contain any Auto Scaling groups
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Auto Scaling Group resource
#       And: 'LoadBalancerNames' or 'TargetGroupARNs' are not present on the Auto Scaling Group resource or empty lists
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Auto Scaling Group resource
#       And: 'LoadBalancerNames' or 'TargetGroupARNs' are present on the Auto Scaling group with at least
#            one configuration
#       And: 'HealthCheckType' is not present
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Auto Scaling Group resource
#       And: 'LoadBalancerNames' or 'TargetGroupARNs' are present on the Auto Scaling group with at least
#            one configuration
#       And: 'HealthCheckType' is present and set to a value other than 'ELB' (e.g. 'EC2')
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Auto Scaling Group resource
#       And: 'LoadBalancerNames' or 'TargetGroupARNs' are present on the Auto Scaling Group resource with at least
#            one configuration
#       And: 'HealthCheckType' is present and set to 'ELB'
#      Then: PASS

#
# Constants
#
let AUTOSCALING_GROUP_TYPE = "AWS::AutoScaling::AutoScalingGroup"
let INPUT_DOCUMENT = this

#
# Assignments
#
let autoscaling_groups = Resources.*[ Type == %AUTOSCALING_GROUP_TYPE ]

#
# Primary Rules
#
rule autoscaling_group_elb_healthcheck_required_check when is_cfn_template(%INPUT_DOCUMENT)
                                                           %autoscaling_groups not empty {
    check(%autoscaling_groups.Properties)
        <<
        [CT.AUTOSCALING.PR.4]: Require an Amazon EC2 Auto Scaling group associated with an AWS Elastic Load Balancer (ELB) to have ELB health checks activated
        [FIX]: Configure Amazon EC2 Auto Scaling groups associated with an Elastic Load Balancing load balancer to use Elastic Load Balancing health checks.
        >>
}

rule autoscaling_group_elb_healthcheck_required_check when is_cfn_hook(%INPUT_DOCUMENT, %AUTOSCALING_GROUP_TYPE) {
    check(this.%AUTOSCALING_GROUP_TYPE.resourceProperties)
        <<
        [CT.AUTOSCALING.PR.4]: Require an Amazon EC2 Auto Scaling group associated with an AWS Elastic Load Balancer (ELB) to have ELB health checks activated
        [FIX]: Configure Amazon EC2 Auto Scaling groups associated with an Elastic Load Balancing load balancer to use Elastic Load Balancing health checks.
        >>
}

#
# Parameterized Rules
#
rule check(autoscaling_group) {
    %autoscaling_group [
        filter_list_exists_and_not_empty(LoadBalancerNames) or
        filter_list_exists_and_not_empty(TargetGroupARNs)
    ] {
       check_healthcheck_type_on_asg(this)
    }
}

rule filter_list_exists_and_not_empty(property) {
    %property {
        # Scenario 2
        this exists
        this is_list
        this not empty
    }
}

rule check_healthcheck_type_on_asg(asg) {
    %asg {
        # Scenario 3
        HealthCheckType exists
        # Scenario 4 and 5
        HealthCheckType == "ELB"
    }
}

#
# Utility Rules
#
rule is_cfn_template(doc) {
    %doc {
        AWSTemplateFormatVersion exists or
        Resources exists
    }
}

rule is_cfn_hook(doc, RESOURCE_TYPE) {
    %doc.%RESOURCE_TYPE.resourceProperties exists
}