# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   elasticsearch_in_vpc_only_check
# 
# Description:
#   This control checks whether Elasticsearch domains are configured with VPC option settings that specify a target Amazon VPC.
# 
# 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: 'VPCOptions' 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: 'VPCOptions' has been provided
#       And: 'SubnetIds' in 'VPCOptions' has not been provided or has been provided
#            as 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 Elasticsearch domain resource
#       And: 'VPCOptions' has been provided
#       And: 'SubnetIds' in 'VPCOptions' has been provided as a list with one or more values
#      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_in_vpc_only_check when is_cfn_template(%INPUT_DOCUMENT)
                                          %elasticsearch_domains not empty {
    check(%elasticsearch_domains.Properties)
        <<
        [CT.OPENSEARCH.PR.2]: Require an Elasticsearch domain to be created in a user-specified Amazon VPC
        [FIX]: Within 'VPCOptions', set 'SubnetIds' to a list with one or more Amazon EC2 subnet IDs.
        >>
}

rule elasticsearch_in_vpc_only_check when is_cfn_hook(%INPUT_DOCUMENT, %ELASTICSEARCH_DOMAIN_TYPE) {
    check(%INPUT_DOCUMENT.%ELASTICSEARCH_DOMAIN_TYPE.resourceProperties)
        <<
        [CT.OPENSEARCH.PR.2]: Require an Elasticsearch domain to be created in a user-specified Amazon VPC
        [FIX]: Within 'VPCOptions', set 'SubnetIds' to a list with one or more Amazon EC2 subnet IDs.
        >>
}

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

        VPCOptions {
            # Scenarios 3 and 4
            SubnetIds exists
            SubnetIds is_list
            SubnetIds 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
}