# ###################################
##       Rule Specification        ##
#####################################
# Rule Identifier:
#   efs_encrypted_check
# 
# Description:
#   This control checks whether an Amazon EFS file system is configured to encrypt file data using AWS KMS.
# 
# Reports on:
#   AWS::EFS::FileSystem
# 
# 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 EFS file system resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EFS file system resource
#       And: 'Encrypted' is not present
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EFS file system resource
#       And: 'Encrypted' is present and set to bool(false)
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EFS file system resource
#       And: 'Encrypted' is present and set to bool(true)
#      Then: PASS

#
# Constants
#
let RESOURCE_TYPE = "AWS::EFS::FileSystem"
let INPUT_DOCUMENT = this

#
# Assignments
#
let efs_file_systems = Resources.*[ Type == %RESOURCE_TYPE ]

#
# Primary Rules
#
rule efs_encrypted_check when is_cfn_template(%INPUT_DOCUMENT)
                              %efs_file_systems not empty {
    check(%efs_file_systems.Properties)
        <<
        [CT.ELASTICFILESYSYSTEM.PR.1]: Require an Amazon EFS file system to encrypt file data at rest using AWS KMS
        [FIX]: Set 'Encrypted' to 'true' and optionally set 'KmsKeyId' to a valid AWS KMS key identifier.
        >>
}

rule efs_encrypted_check when is_cfn_hook(%INPUT_DOCUMENT, %RESOURCE_TYPE) {
    check(%INPUT_DOCUMENT.%RESOURCE_TYPE.resourceProperties)
        <<
        [CT.ELASTICFILESYSYSTEM.PR.1]: Require an Amazon EFS file system to encrypt file data at rest using AWS KMS
        [FIX]: Set 'Encrypted' to 'true' and optionally set 'KmsKeyId' to a valid AWS KMS key identifier.
        >>
}

#
# Parameterized Rules
#
rule check(efs_file_systems) {
    %efs_file_systems {
        # Scenario 2
        Encrypted exists
        # Scenario 3 and 4
        Encrypted == true
    }
}

#
# 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
}