# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   s3_event_notifications_enabled_check
# 
# Description:
#   This control checks whether Amazon S3 events notifications are enabled on your Amazon S3 bucket.
# 
# Reports on:
#   AWS::S3::Bucket
# 
# 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 S3 bucket resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon S3 bucket resource
#       And: 'NotificationConfiguration' 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 an Amazon S3 bucket resource
#       And: 'NotificationConfiguration' has been provided
#       And:  At least one of 'EventBridgeConfiguration.EventBridgeEnabled', 'LambdaConfigurations',
#             'QueueConfigurations', or 'TopicConfigurations' have not been provided or provided as empty lists.
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon S3 bucket resource
#       And: 'NotificationConfiguration' has been provided
#       And: 'EventBridgeConfiguration.EventBridgeEnabled' is set to bool(true) or 'LambdaConfigurations',
#            'QueueConfigurations', or 'TopicConfigurations' have been provided with at least one configuration
#      Then: PASS

#
# Constants
#
let S3_BUCKET_TYPE = "AWS::S3::Bucket"
let INPUT_DOCUMENT = this

#
# Assignments
#
let s3_buckets = Resources.*[ Type == %S3_BUCKET_TYPE ]

#
# Primary Rules
#
rule s3_event_notifications_enabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                               %s3_buckets not empty {
    check(%s3_buckets.Properties)
        <<
        [CT.S3.PR.4]: Require an Amazon S3 bucket to have event notifications configured
        [FIX]: Set a 'NotificationConfiguration' parameter on your bucket with one of 'EventBridgeConfiguration', 'LambdaConfigurations', 'QueueConfigurations' or 'TopicConfigurations.'
        >>
}

rule s3_event_notifications_enabled_check when is_cfn_hook(%INPUT_DOCUMENT, %S3_BUCKET_TYPE) {
    check(%INPUT_DOCUMENT.%S3_BUCKET_TYPE.resourceProperties)
        <<
        [CT.S3.PR.4]: Require an Amazon S3 bucket to have event notifications configured
        [FIX]: Set a 'NotificationConfiguration' parameter on your bucket with one of 'EventBridgeConfiguration', 'LambdaConfigurations', 'QueueConfigurations' or 'TopicConfigurations.'
        >>
}

#
# Parameterized Rules
#
rule check(s3_bucket) {
    %s3_bucket {
       # Scenario 2
       NotificationConfiguration exists
       NotificationConfiguration is_struct
       NotificationConfiguration {
            # Scenario 3 and 4
            EventBridgeConfiguration exists or
            LambdaConfigurations exists or
            QueueConfigurations exists or
            TopicConfigurations exists

            check_event_bridge_notifications(EventBridgeConfiguration) or
            check_other_notifications(LambdaConfigurations) or
            check_other_notifications(QueueConfigurations) or
            check_other_notifications(TopicConfigurations)
       }
    }
}

rule check_event_bridge_notifications(configuration) {
    %configuration {
        this is_struct
        EventBridgeEnabled exists
        EventBridgeEnabled == true
    }
}

rule check_other_notifications(configuration) {
    %configuration {
        this is_list
        this not empty
    }
}

#
# 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
}