# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   ec2_launch_template_public_ip_disabled_check
# 
# Description:
#   This control checks whether your Amazon EC2 launch templates are configured to assign public IP addresses to network interfaces.
# 
# Reports on:
#   AWS::EC2::LaunchTemplate
# 
# 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 Amazon EC2 launch template resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon EC2 launch template resource
#       And: 'NetworkInterfaces' is not provided in 'LaunchTemplateData'
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon EC2 launch template resource
#       And: 'LaunchTemplateData.NetworkInterfaces' is present on the Amazon EC2 launch template resource as a non empty list
#       And: 'NetworkInterfaceId' is present for a configuration in 'NetworkInterfaces' and is a non-empty string or
#             valid local reference
#      Then: SKIP
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon EC2 launch template resource
#       And: 'LaunchTemplateData.NetworkInterfaces' is present on the Amazon EC2 launch template resource
#       And: 'NetworkInterfaceId' is not present or is present and is an empty string or invalid local reference for
#            a configuration in 'NetworkInterfaces'
#       And: 'AssociatePublicIpAddress' is not present for a configuration in 'NetworkInterfaces'
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon EC2 launch template resource
#       And: 'LaunchTemplateData.NetworkInterfaces' is present on the Amazon EC2 launch template resource
#       And: 'NetworkInterfaceId' is not present or is present and is an empty string or invalid local reference for
#            a configuration in 'NetworkInterfaces'
#       And: 'AssociatePublicIpAddress' is present for a configuration in 'NetworkInterfaces'
#       And: 'AssociatePublicIpAddress' is set to bool(true)
#      Then: FAIL
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon EC2 launch template resource
#       And: 'LaunchTemplateData.NetworkInterfaces' is present on the Amazon EC2 launch template resource
#       And: 'NetworkInterfaceId' is not present or is present and is an empty string or invalid local reference for
#            a configuration in 'NetworkInterfaces'
#       And: 'AssociatePublicIpAddress' is present for a configuration in 'NetworkInterfaces'
#       And: 'AssociatePublicIpAddress' is set to bool(false)
#      Then: PASS

#
# Constants
#
let EC2_LAUNCH_TEMPLATE_TYPE = "AWS::EC2::LaunchTemplate"
let INPUT_DOCUMENT = this

#
# Assignments
#
let ec2_launch_templates = Resources.*[ Type == %EC2_LAUNCH_TEMPLATE_TYPE ]

#
# Primary Rules
#
rule ec2_launch_template_public_ip_disabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                                       %ec2_launch_templates not empty {
    check(%ec2_launch_templates.Properties)
        <<
        [CT.EC2.PR.9]: Require any Amazon EC2 launch template not to auto-assign public IP addresses to network interfaces
        [FIX]: Set 'AssociatePublicIpAddress' to 'false' within each 'NetworkInterfaces' configuration in 'LaunchTemplateData'.
        >>
}

rule ec2_launch_template_public_ip_disabled_check when is_cfn_hook(%INPUT_DOCUMENT, %EC2_LAUNCH_TEMPLATE_TYPE) {
    check(%INPUT_DOCUMENT.%EC2_LAUNCH_TEMPLATE_TYPE.resourceProperties)
        <<
        [CT.EC2.PR.9]: Require any Amazon EC2 launch template not to auto-assign public IP addresses to network interfaces
        [FIX]: Set 'AssociatePublicIpAddress' to 'false' within each 'NetworkInterfaces' configuration in 'LaunchTemplateData'.
        >>
}

#
# Parameterized Rules
#
rule check(ec2_launch_templates) {
    %ec2_launch_templates[
        # Scenario 2
        filter_launch_template(this)
    ] {
        LaunchTemplateData {
            NetworkInterfaces[
                # Scenario 3 and 4
                filter_network_interfaces(this)
            ] {
                # Scenario 5 and 6
                AssociatePublicIpAddress exists
                AssociatePublicIpAddress == false
            }
        }
    }
}

rule filter_launch_template(ec2_launch_template) {
    %ec2_launch_template {
        LaunchTemplateData exists
        LaunchTemplateData is_struct
        LaunchTemplateData {
            NetworkInterfaces exists
            NetworkInterfaces is_list
            NetworkInterfaces not empty
        }
    }
}

rule filter_network_interfaces(network_interface) {
    %network_interface {
        NetworkInterfaceId not exists or
        filter_property_is_empty_string(NetworkInterfaceId) or
        filter_exclude_valid_local_reference(%INPUT_DOCUMENT, NetworkInterfaceId, "AWS::EC2::NetworkInterface")
    }
}

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

rule filter_exclude_valid_local_reference(doc, reference_properties, referenced_resource_type) {
    %reference_properties {
        this not is_string
        this is_struct

        when this.'Fn::GetAtt' exists {
            'Fn::GetAtt' {
                when query_for_resource(%doc, this[0], %referenced_resource_type) {
                    this not exists
                }
                this exists
            }
        }
        when this.'Fn::GetAtt' not exists {
            this exists
        }
    }
}

#
# 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 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
    }
}