# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   rds_cluster_event_notifications_configured_check
# 
# Description:
#   This control checks whether your Amazon RDS event subscriptions for RDS clusters are configured to notify on event categories of 'maintenance' and 'failure.'
# 
# Reports on:
#   AWS::RDS::EventSubscription
# 
# 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 RDS event subscription resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon RDS event subscription resource
#       And: 'SourceType' is provided and is not 'db-cluster'
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon RDS event subscription resource
#       And: 'SourceType' is 'db-cluster'
#       And: 'Enabled' is not provided or 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 Amazon RDS event subscription resource
#       And: 'SourceType' is provided and is 'db-cluster'
#       And: 'Enabled' is provided and set to bool(true)
#       And: 'EventCategories' does not contain both 'maintenance' and 'failure'
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon RDS event subscription resource
#       And: 'SourceType' is provided and is 'db-cluster'
#       And: 'Enabled' is provided and set to bool(true)
#       And: 'EventCategories' does not exist or is an empty list
#      Then: PASS
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon RDS event subscription resource
#       And: 'SourceType' is provided and is 'db-cluster'
#       And: 'Enabled' is provided and set to bool(true)
#       And: 'EventCategories' contains both 'maintenance' and 'failure'
#      Then: PASS

#
# Constants
#
let RDS_EVENTSUBSCRIPTION_TYPE = "AWS::RDS::EventSubscription"
let INPUT_DOCUMENT = this
let EVENT_CATEGORIES = ["maintenance","failure"]
let EVENT_SOURCE_TYPE = "db-cluster"

#
# Assignments
#
let rds_event_subscriptions = Resources.*[ Type == %RDS_EVENTSUBSCRIPTION_TYPE ]

#
# Primary Rules
#
rule rds_cluster_event_notifications_configured_check when is_cfn_template(%INPUT_DOCUMENT)
                                                           %rds_event_subscriptions not empty {
    check(%rds_event_subscriptions.Properties)
        <<
        [CT.RDS.PR.12]: Require an Amazon RDS event subscription to have critical cluster events configured
        [FIX]: When 'SourceType' is set to 'db-cluster', set 'Enabled' to true and ensure that 'EventCategories' contains both 'maintenance' and 'failure' values.
        >>
}

rule rds_cluster_event_notifications_configured_check when is_cfn_hook(%INPUT_DOCUMENT, %RDS_EVENTSUBSCRIPTION_TYPE) {
    check(%INPUT_DOCUMENT.%RDS_EVENTSUBSCRIPTION_TYPE.resourceProperties)
        <<
        [CT.RDS.PR.12]: Require an Amazon RDS event subscription to have critical cluster events configured
        [FIX]: When 'SourceType' is set to 'db-cluster', set 'Enabled' to true and ensure that 'EventCategories' contains both 'maintenance' and 'failure' values.
        >>
}

#
# Parameterized Rules
#
rule check(resource) {
    %resource [ SourceType == %EVENT_SOURCE_TYPE ] {
        Enabled exists
        # Scenario 4
        Enabled == true
        # Scenario 5
        EventCategories not exists or
        # Scenario 6
        check_event_categories_for_required_events(EventCategories)
    }
}

rule check_event_categories_for_required_events(event_categories) {
    %event_categories {
        this exists
        this is_list
        this empty or
        %EVENT_CATEGORIES.* in this
    }
}

#
# 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
}