# ###################################
##       Rule Specification        ##
#####################################
# 
# 
# Rule Identifier:
#   subnet_auto_assign_public_ip_disabled_check
# 
# Description:
#   This control checks whether your Amazon VPC subnets automatically assign public IP addresses.
# 
# Reports on:
#   AWS::EC2::Subnet
# 
# 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 EC2 subnet resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EC2 subnet resource
#       And: 'MapPublicIpOnLaunch' is present and set to bool(true)
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EC2 subnet resource
#       And: 'MapPublicIpOnLaunch' is not present
#      Then: PASS
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EC2 subnet resource
#       And: 'MapPublicIpOnLaunch' is present and set to bool(false)
#      Then: PASS

#
# Constants
#
let EC2_SUBNET_TYPE  = "AWS::EC2::Subnet"
let INPUT_DOCUMENT = this

#
# Assignments
#
let ec2_subnets = Resources.*[ Type == %EC2_SUBNET_TYPE ]

#
# Primary Rules
#
rule subnet_auto_assign_public_ip_disabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                                      %ec2_subnets not empty {
    check(%ec2_subnets.Properties)
        <<
        [CT.EC2.PR.11]: Require that an Amazon EC2 subnet does not automatically assign public IP addresses
        [FIX]: Omit the 'MapPublicIpOnLaunch' property to use the default configuration, or set the 'MapPublicIpOnLaunch' property to 'false'.
        >>
}

rule subnet_auto_assign_public_ip_disabled_check when is_cfn_hook(%INPUT_DOCUMENT, %EC2_SUBNET_TYPE) {
    check(%INPUT_DOCUMENT.%EC2_SUBNET_TYPE.resourceProperties)
        <<
        [CT.EC2.PR.11]: Require that an Amazon EC2 subnet does not automatically assign public IP addresses
        [FIX]: Omit the 'MapPublicIpOnLaunch' property to use the default configuration, or set the 'MapPublicIpOnLaunch' property to 'false'.
        >>
}

#
# Parameterized Rules
#
rule check(ec2_subnet) {
    %ec2_subnet {
        # Scenario 3
        MapPublicIpOnLaunch not exists or
        # Scenarios 2 and 4
        MapPublicIpOnLaunch == false
    }
}

#
# 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
}