# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   elbv2_logging_enabled_check
# 
# Description:
#   This control checks whether your ELB application and network load balancers have logging activated.
# 
# Reports on:
#   AWS::ElasticLoadBalancingV2::LoadBalancer
# 
# 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 ElasticLoadBalancingV2 LoadBalancer resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ELBv2 LoadBalancer resource
#       And: 'Type' is set to a value other than 'application' or 'network'
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancingV2 LoadBalancer resource
#       And: The LoadBalancer is of type 'application' or 'network'
#       And: 'LoadBalancerAttributes' has not been provided or is an empty list
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancingV2 LoadBalancer resource
#       And: The LoadBalancer is of type 'application' or 'network'
#       And: A 'LoadBalancerAttributes' with Key 'access_logs.s3.enabled' and 'access_logs.s3.bucket'
#            has not been provided
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancingV2 LoadBalancer resource
#       And: The LoadBalancer is of type 'application' or 'network'
#       And: A 'LoadBalancerAttributes' with Key 'access_logs.s3.enabled' and 'access_logs.s3.bucket' has been provided
#       And: 'access_logs.s3.enabled' is set to bool(false) or string(false)
#      Then: FAIL
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancingV2 LoadBalancer resource
#       And: The LoadBalancer is of type 'application' or 'network'
#       And: A 'LoadBalancerAttributes' with Key 'access_logs.s3.enabled' and 'access_logs.s3.bucket' has been provided
#       And: 'access_logs.s3.enabled' is set to bool(true) or string(true)
#       And: 'access_logs.s3.bucket' is missing or an empty string value
#      Then: FAIL
#   Scenario: 7
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancingV2 LoadBalancer resource
#       And: The LoadBalancer is of type 'application'
#       And: A 'LoadBalancerAttributes' with Key 'access_logs.s3.enabled' has been provided
#       And: 'access_logs.s3.enabled' is set to bool(true) or string(true)
#       And: 'access_logs.s3.bucket' is provided and a non-empty string value or valid local reference
#      Then: PASS

#
# Constants
#
let ELASTIC_LOAD_BALANCER_V2_TYPE = "AWS::ElasticLoadBalancingV2::LoadBalancer"
let INPUT_DOCUMENT = this

#
# Assignments
#
let elastic_load_balancers = Resources.*[ Type == %ELASTIC_LOAD_BALANCER_V2_TYPE ]

#
# Primary Rules
#
rule elbv2_logging_enabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                      %elastic_load_balancers not empty {

    check(%elastic_load_balancers.Properties)
        <<
        [CT.ELASTICLOADBALANCING.PR.6]: Require that application and network load balancer access logging is activated
        [FIX]: Set the load balancer attribute 'access_logs.s3.enabled' to 'true', and set 'access_logs.s3.bucket' to reach an Amazon S3 bucket that's configured to receive application load balancer or network load balancer access logs.
        >>
}

rule elbv2_logging_enabled_check when is_cfn_hook(%INPUT_DOCUMENT, %ELASTIC_LOAD_BALANCER_V2_TYPE) {

    check(%INPUT_DOCUMENT.%ELASTIC_LOAD_BALANCER_V2_TYPE.resourceProperties)
        <<
        [CT.ELASTICLOADBALANCING.PR.6]: Require that application and network load balancer access logging is activated
        [FIX]: Set the load balancer attribute 'access_logs.s3.enabled' to 'true', and set 'access_logs.s3.bucket' to reach an Amazon S3 bucket that's configured to receive application load balancer or network load balancer access logs.
        >>
}

#
# Parameterized Rules
#
rule check(elastic_load_balancer) {
    %elastic_load_balancer[ Type in ["application", "network"] ] {
        # Scenario 3
        LoadBalancerAttributes exists
        LoadBalancerAttributes is_list
        LoadBalancerAttributes not empty

        # Scenario 4, 5, 6 and 7
        some LoadBalancerAttributes[*] {
            Key exists
            Value exists

            Key == "access_logs.s3.enabled"
            Value in [ true, "true" ]
        }

        some LoadBalancerAttributes[*] {
            Key exists
            Value exists

            Key == "access_logs.s3.bucket"
            check_is_string_and_not_empty(Value) or
            check_local_references(%INPUT_DOCUMENT, Value, "AWS::S3::Bucket")
        }
    }
}

#
# 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
}

rule check_is_string_and_not_empty(value) {
    %value {
        this is_string
        this != /\A\s*\z/
    }
}

rule check_local_references(doc, reference_properties, referenced_resource_type) {
    %reference_properties {
        'Fn::GetAtt' {
            query_for_resource(%doc, this[0], %referenced_resource_type)
                <<Local Stack reference was invalid>>
        } or Ref {
            query_for_resource(%doc, this, %referenced_resource_type)
                <<Local Stack reference was invalid>>
        }
    }
}

rule query_for_resource(doc, resource_key, referenced_resource_type) {
    let referenced_resource = %doc.Resources[ keys == %resource_key ]
    %referenced_resource not empty
    %referenced_resource {
        Type == %referenced_resource_type
    }
}