# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   dynamodb_table_encrypted_kms_check
# 
# Description:
#   This control checks whether your Amazon DynamoDB table is encrypted with an AWS Key Management Service (KMS) key.
# 
# Reports on:
#   AWS::DynamoDB::Table
# 
# 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 DynamoDB table resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a DynamoDB table resources
#       And: 'SSEEnabled' in 'SSESpecification' has not been provided
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a DynamoDB table resources
#       And: 'SSEEnabled' in 'SSESpecification' has been provided and set to a value other than bool(true)
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a DynamoDB table resources
#       And: 'SSEEnabled' in 'SSESpecification' has been provided and set to bool(true)
#      Then: PASS

#
# Constants
#
let DYNAMODB_TABLE_TYPE = "AWS::DynamoDB::Table"
let INPUT_DOCUMENT = this

#
# Assignments
#
let dynamodb_tables = Resources.*[ Type == %DYNAMODB_TABLE_TYPE ]

#
# Primary Rules
#
rule dynamodb_table_encrypted_kms_check when is_cfn_template(%INPUT_DOCUMENT)
                                             %dynamodb_tables not empty {
    check(%dynamodb_tables.Properties)
        <<
        [CT.DYNAMODB.PR.2]: Require an Amazon DynamoDB table to be encrypted at rest using an AWS KMS key
        [FIX]: Provide a 'SSESpecification' configuration and set 'SSEEnabled' to 'true'.
        >>
}

rule dynamodb_table_encrypted_kms_check when is_cfn_hook(%INPUT_DOCUMENT, %DYNAMODB_TABLE_TYPE) {
    check(%INPUT_DOCUMENT.%DYNAMODB_TABLE_TYPE.resourceProperties)
        <<
        [CT.DYNAMODB.PR.2]: Require an Amazon DynamoDB table to be encrypted at rest using an AWS KMS key
        [FIX]: Provide a 'SSESpecification' configuration and set 'SSEEnabled' to 'true'.
        >>
}

rule check(dynamodb_table) {
    %dynamodb_table {
        # Scenario 2
        SSESpecification exists
        SSESpecification is_struct

        # Scenarios 3 and 4
        SSESpecification {
            SSEEnabled exists
            SSEEnabled == true
        }
    }
}

#
# Utility Rules
#
rule is_cfn_template(doc) {
    %doc {
        AWSTemplateFormatVersion exists  or
        Resources exists
    }
}

rule is_cfn_hook(doc, DYNAMODB_TABLE_TYPE) {
    %doc.%DYNAMODB_TABLE_TYPE.resourceProperties exists
}