# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   sagemaker_notebook_no_direct_internet_access_check
# 
# Description:
#   This control checks that direct internet access is not allowed for an Amazon SageMaker notebook instance.
# 
# Reports on:
#   AWS::SageMaker::NotebookInstance
# 
# 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 SageMaker notebook instance resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an SageMaker notebook instance resource
#       And: 'DirectInternetAccess' has not been provided on the SageMaker notebook instance resource
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an SageMaker notebook instance resource
#       And: 'DirectInternetAccess' has been provided on the SageMaker notebook instance resource
#       And: 'DirectInternetAccess' is set to 'Enabled'
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an SageMaker notebook instance resource
#       And: 'DirectInternetAccess' has been provided on the SageMaker notebook instance resource
#       And: 'DirectInternetAccess' is set to 'Disabled'
#       And: 'SecurityGroupIds' have been provided as a non-empty list with non-empty strings or valid local references
#       And: 'SubnetId' has been provided as an empty string or non-valid local reference
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an SageMaker notebook instance resource
#       And: 'DirectInternetAccess' has been provided on the SageMaker notebook instance resource
#       And: 'DirectInternetAccess' is set to 'Disabled'
#       And: 'SubnetId' has been provided as a non-empty string or valid local reference
#       And: 'SecurityGroupIds' have been provided as an empty list or a list that contains empty string values or
#            non-valid local references
#      Then: FAIL
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an SageMaker notebook instance resource
#       And: 'DirectInternetAccess' has been provided on the SageMaker notebook instance resource
#       And: 'DirectInternetAccess' is set to 'Disabled'
#       And: 'SecurityGroupIds' have been provided as a non-empty list with non-empty strings or valid local references
#       And: 'SubnetId' has been provided as a non-empty string or valid local reference
#      Then: PASS

#
# Constants
#
let SAGEMAKER_NOTEBOOK_INSTANCE_TYPE = "AWS::SageMaker::NotebookInstance"
let INPUT_DOCUMENT = this

#
# Assignments
#
let sagemaker_notebook_instances = Resources.*[ Type == %SAGEMAKER_NOTEBOOK_INSTANCE_TYPE ]

#
# Primary Rules
#
rule sagemaker_notebook_no_direct_internet_access_check when is_cfn_template(this)
                                                             %sagemaker_notebook_instances not empty {
    check(%sagemaker_notebook_instances.Properties)
        <<
        [CT.SAGEMAKER.PR.1]: Require an Amazon SageMaker notebook instance to prevent direct internet access
        [FIX]: Set the value of 'DirectInternetAccess' to 'Disabled' and provide a 'SubnetId' and one or more 'SecurityGroupIds'.
        >>
}

rule sagemaker_notebook_no_direct_internet_access_check when is_cfn_hook(%INPUT_DOCUMENT, %SAGEMAKER_NOTEBOOK_INSTANCE_TYPE) {
    check(%INPUT_DOCUMENT.%SAGEMAKER_NOTEBOOK_INSTANCE_TYPE.resourceProperties)
        <<
        [CT.SAGEMAKER.PR.1]: Require an Amazon SageMaker notebook instance to prevent direct internet access
        [FIX]: Set the value of 'DirectInternetAccess' to 'Disabled' and provide a 'SubnetId' and one or more 'SecurityGroupIds'.
        >>
}

#
# Parameterized Rules
#
rule check(sagemaker_notebook_instances) {
    %sagemaker_notebook_instances {
        # Scenario 2
        DirectInternetAccess exists

        # Scenario 3
        DirectInternetAccess is_string
        DirectInternetAccess == "Disabled"

        # Scenario 4,5 and 6
        check_is_string_and_not_empty(SubnetId) or
        check_local_references(%INPUT_DOCUMENT, SubnetId, "AWS::EC2::Subnet")

        SecurityGroupIds exists
        SecurityGroupIds is_list
        SecurityGroupIds not empty

        SecurityGroupIds[*] {
            check_is_string_and_not_empty(this) or
            check_local_references(%INPUT_DOCUMENT, this, "AWS::EC2::SecurityGroup")
        }
    }
}

#
# Utility Rules
#
rule is_cfn_template(doc) {
    %doc {
        AWSTemplateFormatVersion exists  or
        Resources exists
    }
}

rule is_cfn_hook(doc, SAGEMAKER_NOTEBOOK_INSTANCE_TYPE) {
    %doc.%SAGEMAKER_NOTEBOOK_INSTANCE_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
    }
}