# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   elasticsearch_application_logging_enabled_check
# 
# Description:
#   This control checks whether Elasticsearch domains are configured to send error logs to an Amazon CloudWatch Logs log group.
# 
# Reports on:
#   AWS::Elasticsearch::Domain
# 
# 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 Elasticsearch domain resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Elasticsearch domain resource
#       And: 'LogPublishingOptions' 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 Elasticsearch domain resource
#       And: 'LogPublishingOptions' has been provided
#       And: 'ES_APPLICATION_LOGS' in 'LogPublishingOptions' has not been provided
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Elasticsearch domain resource
#       And: 'LogPublishingOptions' has been specified
#       And: 'ES_APPLICATION_LOGS' in 'LogPublishingOptions' has been provided
#       And: 'Enabled' in 'ES_APPLICATION_LOGS' has not been provided or provided and set to
#            a value other than bool(true)
#       And: 'CloudWatchLogsLogGroupArn' in 'ES_APPLICATION_LOGS' has not been provided or provided
#            as an empty string or invalid local reference
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Elasticsearch domain resource
#       And: 'LogPublishingOptions' has been specified
#       And: 'ES_APPLICATION_LOGS' in 'LogPublishingOptions' has been provided
#       And: 'Enabled' in 'ES_APPLICATION_LOGS' has been provided and set to bool(true)
#       And: 'CloudWatchLogsLogGroupArn' in 'ES_APPLICATION_LOGS' has not been provided or provided
#            as an empty string or invalid local reference
#      Then: FAIL
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Elasticsearch domain resource
#       And: 'LogPublishingOptions' has been specified
#       And: 'ES_APPLICATION_LOGS' in 'LogPublishingOptions' has been provided
#       And: 'Enabled' in 'ES_APPLICATION_LOGS' has not been provided or provided and set to
#            a value other than bool(true)
#       And: 'CloudWatchLogsLogGroupArn' in 'ES_APPLICATION_LOGS' has been provided as a non-empty string
#            or valid local reference
#      Then: FAIL
#   Scenario: 7
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Elasticsearch domain resource
#       And: 'LogPublishingOptions' has been specified
#       And: 'ES_APPLICATION_LOGS' in 'LogPublishingOptions' has been provided
#       And: 'Enabled' in 'ES_APPLICATION_LOGS' has been provided and set to bool(true)
#       And: 'CloudWatchLogsLogGroupArn' in 'ES_APPLICATION_LOGS' has been provided as a non-empty string
#            or valid local reference
#      Then: PASS

#
# Constants
#
let ELASTICSEARCH_DOMAIN_TYPE = "AWS::Elasticsearch::Domain"
let INPUT_DOCUMENT = this

#
# Assignments
#
let elasticsearch_domains = Resources.*[ Type == %ELASTICSEARCH_DOMAIN_TYPE ]

#
# Primary Rules
#
rule elasticsearch_application_logging_enabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                                          %elasticsearch_domains not empty {
    check(%elasticsearch_domains.Properties)
        <<
        [CT.OPENSEARCH.PR.4]: Require an Elasticsearch domain to send error logs to Amazon CloudWatch Logs
        [FIX]: Within 'LogPublishingOptions', provide an 'ES_APPLICATION_LOGS' configuration, set 'Enabled' to 'true', and set 'CloudWatchLogsLogGroupArn' to the ARN of a valid Amazon CloudWatch Logs log group.
        >>
}

rule elasticsearch_application_logging_enabled_check when is_cfn_hook(%INPUT_DOCUMENT, %ELASTICSEARCH_DOMAIN_TYPE) {
    check(%INPUT_DOCUMENT.%ELASTICSEARCH_DOMAIN_TYPE.resourceProperties)
        <<
        [CT.OPENSEARCH.PR.4]: Require an Elasticsearch domain to send error logs to Amazon CloudWatch Logs
        [FIX]: Within 'LogPublishingOptions', provide an 'ES_APPLICATION_LOGS' configuration, set 'Enabled' to 'true', and set 'CloudWatchLogsLogGroupArn' to the ARN of a valid Amazon CloudWatch Logs log group.
        >>
}

#
# Parameterized Rules
#
rule check(elasticsearch_domain) {
    %elasticsearch_domain {
        # Scenario 2
        LogPublishingOptions exists
        LogPublishingOptions is_struct

        LogPublishingOptions {
            # Scenario 3
            ES_APPLICATION_LOGS exists
            ES_APPLICATION_LOGS is_struct

            ES_APPLICATION_LOGS {
                # Scenarios 4, 5, 6 and 7
                Enabled exists
                Enabled == true

                CloudWatchLogsLogGroupArn exists
                check_is_string_and_not_empty(CloudWatchLogsLogGroupArn) or
                check_local_references(%INPUT_DOCUMENT, CloudWatchLogsLogGroupArn, "AWS::Logs::LogGroup")
            }
        }
    }
}

#
# 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
}

rule check_is_string_and_not_empty(value) {
    %value {
        this is_string
        this != /\A\s*\z/
    }
}

rule check_local_references(doc, reference_properties, referenced_resource_type) {
    %reference_properties {
        'Fn::GetAtt' {
            query_for_resource(%doc, this[0], %referenced_resource_type)
                <<Local Stack reference was invalid>>
        } or Ref {
            query_for_resource(%doc, this, %referenced_resource_type)
                <<Local Stack reference was invalid>>
        }
    }
}

rule query_for_resource(doc, resource_key, referenced_resource_type) {
    let referenced_resource = %doc.Resources[ keys == %resource_key ]
    %referenced_resource not empty
    %referenced_resource {
        Type == %referenced_resource_type
    }
}