# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   elb_logging_enabled_check
# 
# Description:
#   This control checks whether classic load balancers have logging enabled.
# 
# 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 load balancer resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancing load balancer resource
#       And: 'AccessLoggingPolicy' has not been provided
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancing load balancer resource
#       And: 'AccessLoggingPolicy' has been provided
#       And: 'Enabled' in 'AccessLoggingPolicy' is missing or has been set to bool(false) or 'S3BucketName' is missing
#             or empty string value
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancing load balancer resource
#       And: 'AccessLoggingPolicy' has been provided
#       And: 'Enabled' has been provided in 'AccessLoggingPolicy' and has been set to bool(true)
#       And: 'S3BucketName' has been provided in 'AccessLoggingPolicy' as a non-empty string value or
#            valid local reference
#      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_logging_enabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                    %classic_load_balancers not empty {
    check(%classic_load_balancers.Properties)
        <<
        [CT.ELASTICLOADBALANCING.PR.10]: Require an ELB application or classic load balancer to have logging activated
        [FIX]: Set an 'AccessLoggingPolicy' and provide an 'S3BucketName' with an Amazon S3 bucket configured to receive classic load balancer access logs.
        >>

}

rule elb_logging_enabled_check when is_cfn_hook(%INPUT_DOCUMENT, %ELASTIC_LOAD_BALANCER_TYPE) {
    check(%INPUT_DOCUMENT.%ELASTIC_LOAD_BALANCER_TYPE.resourceProperties)
        <<
        [CT.ELASTICLOADBALANCING.PR.10]: Require an ELB application or classic load balancer to have logging activated
        [FIX]: Set an 'AccessLoggingPolicy' and provide an 'S3BucketName' with an Amazon S3 bucket configured to receive classic load balancer access logs.
        >>
}

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

        AccessLoggingPolicy {
            # Scenario 3 and 4
            Enabled exists
            Enabled == true

            S3BucketName exists
            check_is_string_and_not_empty(S3BucketName) or
            check_local_references(%INPUT_DOCUMENT, S3BucketName, "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
    }
}