# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   alb_http_to_https_redirection_check
# 
# Description:
#   This control checks whether HTTP to HTTPS redirection is configured as a default action on HTTP listeners of application load balancers.
# 
# Reports on:
#   AWS::ElasticLoadBalancingV2::Listener
# 
# 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 listener resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancingV2 listener
#       And: 'Protocol' is set to a value other than 'HTTP'
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancingV2 listener
#       And: 'Protocol' is set to 'HTTP'
#       And: 'DefaultActions' is missing or is provided and 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 listener
#       And: 'Protocol' is set to 'HTTP'
#       And: 'DefaultActions' contains an action with 'Type' set to a value other than 'redirect'
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancingV2 listener
#       And: 'Protocol' is set to 'HTTP'
#       And: 'DefaultActions' contains an action with 'Type' set to a value of 'redirect'
#       And: 'RedirectConfig.Protocol' is missing or set to a value other than 'HTTPS'
#      Then: FAIL
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElasticLoadBalancingV2 listener
#       And: 'Protocol' is set to 'HTTP'
#       And: All 'DefaultActions' have an action with 'Type' set to a value of 'redirect' and
#            'Protocol.RedirectConfig' set to the value 'HTTPS'
#      Then: PASS

#
# Constants
#
let ELASTIC_LOAD_BALANCER_V2_LISTENER_TYPE = "AWS::ElasticLoadBalancingV2::Listener"
let INPUT_DOCUMENT = this

#
# Assignments
#
let elb_v2_listeners = Resources.*[ Type == %ELASTIC_LOAD_BALANCER_V2_LISTENER_TYPE ]

#
# Primary Rules
#
rule alb_http_to_https_redirection_check when is_cfn_template(%INPUT_DOCUMENT)
                                               %elb_v2_listeners not empty {
    check(%elb_v2_listeners.Properties)
        <<
        [CT.ELASTICLOADBALANCING.PR.1]: Require any application load balancer listener default actions to redirect all HTTP requests to HTTPS
        [FIX]: Configure a default HTTPS redirect action on application load balancer HTTP listeners.
        >>
}

rule alb_http_to_https_redirection_check when is_cfn_hook(%INPUT_DOCUMENT, %ELASTIC_LOAD_BALANCER_V2_LISTENER_TYPE) {
    check(%INPUT_DOCUMENT.%ELASTIC_LOAD_BALANCER_V2_LISTENER_TYPE.resourceProperties)
        <<
        [CT.ELASTICLOADBALANCING.PR.1]: Require any application load balancer listener default actions to redirect all HTTP requests to HTTPS
        [FIX]: Configure a default HTTPS redirect action on application load balancer HTTP listeners.
        >>
}

#
# Parameterized Rules
#
rule check(elbv2_listener) {
    %elbv2_listener [
        # Scenario 2
        Protocol in [ "HTTP" ]
    ] {
        # Scenarios 3
        DefaultActions exists
        DefaultActions is_list
        DefaultActions not empty

        # Scenario 4 and 5
        DefaultActions[*] {
            Type == "redirect"

            RedirectConfig exists
            RedirectConfig is_struct
            RedirectConfig {
                Protocol exists
                Protocol == "HTTPS"
            }
        }
    }
}

#
# 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
}