# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   api_gw_cache_encrypted_check
# 
# Description:
#   This control checks whether an Amazon API Gateway REST API stage that has caching enabled also encrypts the caches.
# 
# Reports on:
#   AWS::ApiGateway::Stage
# 
# 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 API Gateway stage resources
#     Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon API Gateway stage resource
#       And: 'CacheClusterEnabled' is not set, or is set to bool(false) on the API Gateway stage resource
#     Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon API Gateway stage resource
#       And: 'CacheClusterEnabled' is set to bool(true) on the API Gateway stage resource
#       And: In the Stage resource, 'MethodSettings' is not present or is provided and is an empty list.
#     Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon API Gateway stage resource
#       And: 'CacheClusterEnabled' is set to bool(true) on the API Gateway stage resource
#       And: In the stage resource, cache data encryption is not enabled for all HTTP methods and API resources (In
#           'MethodSettings', 'CacheDataEncrypted' is omitted or set to bool(false) for 'HttpMethod' of '*' and
#           'ResourcePath' of '/*' )
#     Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an API Gateway stage resource
#       And: 'CacheClusterEnabled' is set to bool(true) on the API Gateway stage resource
#       And: In the stage resource, cache data encryption is configured for all 'MethodSettings' (CacheDataEncrypted is
#           bool(true) for 'HttpMethod' of '*' and 'ResourcePath' of '/*')
#       And: 'CacheDataEncrypted' has been set to bool(false) for any other method settings
#     Then: FAIL
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an API Gateway stage resource
#       And: 'CacheClusterEnabled' is set to bool(true) on the API Gateway stage resource
#       And: In the stage resource cache data encryption is configured for all 'MethodSettings' (CacheDataEncrypted is
#           bool(true) for 'HttpMethod' of '*' and 'ResourcePath' of '/*')
#       And: 'CacheDataEncrypted' has not been provided or set to bool(true) for all other method settings
#     Then: PASS

#
# Constants
#
let API_GW_STAGE_TYPE = "AWS::ApiGateway::Stage"
let INPUT_DOCUMENT = this

#
# Assignments
#
let api_gateway_stages = Resources.*[ Type == %API_GW_STAGE_TYPE ]

#
# Primary Rules
#
rule api_gw_cache_encrypted_check when is_cfn_template(%INPUT_DOCUMENT)
                                       %api_gateway_stages not empty {
    check(%api_gateway_stages.Properties)
        <<
        [CT.APIGATEWAY.PR.3]: Require that an Amazon API Gateway REST API stage has encryption at rest configured for cache data
        [FIX]: Configure encryption on Amazon API Gateway caches with a 'MethodSetting' that sets 'CacheDataEncrypted' to true for all methods ('HttpMethod' of '*' and 'ResourcePath' of '/*'). Ensure that you do not set 'CacheDataEncrypted' to false for any method setting.
        >>
}

rule api_gw_cache_encrypted_check when is_cfn_hook(%INPUT_DOCUMENT, %API_GW_STAGE_TYPE) {
    check(%INPUT_DOCUMENT.%API_GW_STAGE_TYPE.resourceProperties)
        <<
        [CT.APIGATEWAY.PR.3]: Require that an Amazon API Gateway REST API stage has encryption at rest configured for cache data
        [FIX]: Configure encryption on Amazon API Gateway caches with a 'MethodSetting' that sets 'CacheDataEncrypted' to true for all methods ('HttpMethod' of '*' and 'ResourcePath' of '/*'). Ensure that you do not set 'CacheDataEncrypted' to false for any method setting.
        >>
}

#
# Parameterized Rules
#
rule check(api_gateway_stage) {
    %api_gateway_stage [
        CacheClusterEnabled exists
        CacheClusterEnabled == true
    ] {
        # Scenario 2, 3, 4, 6
        cache_encrypted(this)
    }
}

rule cache_encrypted(api_gateway_stage) {
    %api_gateway_stage {
        MethodSettings exists
        MethodSettings is_list
        MethodSettings not empty

        some MethodSettings[*] {
            HttpMethod exists
            ResourcePath exists
            CacheDataEncrypted exists

            HttpMethod == "*"
            ResourcePath == "/*"
            CacheDataEncrypted == true
        }

        MethodSettings[*] {
            when CacheDataEncrypted exists {
                CacheDataEncrypted == 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
}