# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   netfw_policy_default_action_full_packets_check
# 
# Description:
#   This control checks whether an AWS Network Firewall firewall policy is configured with a user-defined stateless default action for full packets.
# 
# Reports on:
#   AWS::NetworkFirewall::FirewallPolicy
# 
# 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 NetworkFirewall firewall policy resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a NetworkFirewall firewall policy resource
#       And: 'StatelessDefaultActions' has not been provided in 'FirewallPolicy'
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a NetworkFirewall firewall policy resource
#       And: 'StatelessDefaultActions' has been provided in 'FirewallPolicy' as an empty list
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a NetworkFirewall firewall policy resource
#       And: 'StatelessDefaultActions' has been provided in 'FirewallPolicy' as a list that does not contain
#             one of 'aws:drop' or 'aws:forward_to_sfe'
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a NetworkFirewall firewall policy resource
#       And: 'StatelessDefaultActions' has been provided in 'FirewallPolicy' as a list that contains either
#            'aws:drop' or 'aws:forward_to_sfe'
#      Then: PASS


#
# Constants
#
let NETFW_FIREWALL_POLICY_TYPE = "AWS::NetworkFirewall::FirewallPolicy"
let INPUT_DOCUMENT = this
let ALLOWED_STATELESS_ACTIONS_LIST = [ "aws:drop", "aws:forward_to_sfe" ]

#
# Assignments
#
let netfw_firewall_policies = Resources.*[ Type == %NETFW_FIREWALL_POLICY_TYPE ]

#
# Primary Rules
#
rule netfw_policy_default_action_full_packets_check when is_cfn_template(%INPUT_DOCUMENT)
                                                             %netfw_firewall_policies not empty {
    check(%netfw_firewall_policies.Properties)
        <<
        [CT.NETWORK-FIREWALL.PR.2]: Require any AWS Network Firewall firewall policy to drop or forward stateless full packets by default when they do not match a rule
        [FIX]: Within 'FirewallPolicy', include one of 'aws:drop' or 'aws:forward_to_sfe' in 'StatelessDefaultActions'.
        >>
}

rule netfw_policy_default_action_full_packets_check when is_cfn_hook(%INPUT_DOCUMENT, %NETFW_FIREWALL_POLICY_TYPE) {
    check(%INPUT_DOCUMENT.%NETFW_FIREWALL_POLICY_TYPE.resourceProperties)
        <<
        [CT.NETWORK-FIREWALL.PR.2]: Require any AWS Network Firewall firewall policy to drop or forward stateless full packets by default when they do not match a rule
        [FIX]: Within 'FirewallPolicy', include one of 'aws:drop' or 'aws:forward_to_sfe' in 'StatelessDefaultActions'.
        >>
}

#
# Parameterized Rules
#
rule check(netfw_firewall_policy) {
    %netfw_firewall_policy {
        # Scenario 2
        FirewallPolicy exists
        FirewallPolicy is_struct

        FirewallPolicy {
            StatelessDefaultActions exists
            # Scenario 3
            StatelessDefaultActions is_list
            StatelessDefaultActions not empty

            # Scenario 4 and 5
            some StatelessDefaultActions[*] {
                this in %ALLOWED_STATELESS_ACTIONS_LIST
            }
        }
    }
}

#
# 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
}