# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   elb_cross_zone_load_balancing_enabled_check
# 
# Description:
#   This control checks whether cross-zone load balancing is configured for your classic load balancer.
# 
# Reports on:
#   AWS::ElasticLoadBalancing::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 ElasticLoadBalancing LoadBalancer resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancing LoadBalancer resource
#       And: 'CrossZone' has not been specified
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancing LoadBalancer resource
#       And: 'CrossZone' has been specified and set to bool(false)
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancing LoadBalancer resource
#       And: 'CrossZone' has been specified and set to bool(true)
#      Then: PASS

#
# Constants
#
let ELASTIC_LOAD_BALANCER_TYPE = "AWS::ElasticLoadBalancing::LoadBalancer"
let INPUT_DOCUMENT = this

#
# Assignments
#
let classic_load_balancers = Resources.*[ Type == %ELASTIC_LOAD_BALANCER_TYPE ]

#
# Primary Rules
#
rule elb_cross_zone_load_balancing_enabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                                      %classic_load_balancers not empty {
    check(%classic_load_balancers.Properties)
        <<
        [CT.ELASTICLOADBALANCING.PR.13]: Require any ELB classic load balancer to have cross-zone load balancing activated
        [FIX]: Set 'CrossZone' to 'true' on classic load balancers.
        >>
}

rule elb_cross_zone_load_balancing_enabled_check when is_cfn_hook(%INPUT_DOCUMENT, %ELASTIC_LOAD_BALANCER_TYPE) {
    check(%INPUT_DOCUMENT.%ELASTIC_LOAD_BALANCER_TYPE.resourceProperties)
        <<
        [CT.ELASTICLOADBALANCING.PR.13]: Require any ELB classic load balancer to have cross-zone load balancing activated
        [FIX]: Set 'CrossZone' to 'true' on classic load balancers.
        >>
}

#
# Parameterized Rules
#
rule check(classic_load_balancer) {
    %classic_load_balancer {
        # Scenario 2
        CrossZone exists

        # Scenario 3 and 4
        CrossZone == true
    }
}

#
# 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
}