# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   api_gw_v2_access_logs_enabled_check
# 
# Description:
#   This control checks whether Amazon API Gateway V2 stages have access logging enabled. Access logging is supported for HTTP and WebSocket APIs.
# 
# Reports on:
#   AWS::ApiGatewayV2::Stage
# 
# 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 APIGatewayV2 stage resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an APIGatewayV2 stage resource
#       And: 'AccessLogSettings' 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 APIGatewayV2 stage resource
#       And: 'AccessLogSettings' has been provided
#       And: 'AccessLogSettings.DestinationArn' has not been provided, or has been provided as an empty string or
#            invalid local reference
#       And: 'AccessLogSettings.Format' is provided as a non-empty string
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an APIGatewayV2 stage resource
#       And: 'AccessLogSettings' has been provided
#       And: 'AccessLogSettings.DestinationArn' is provided as a non-empty string or valid local reference
#       And: 'AccessLogSettings.Format' has not been provided, or is an empty string
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an APIGatewayV2 stage resource
#       And: 'AccessLogSettings' has been provided
#       And: 'AccessLogSettings.DestinationArn' is provided as a non-empty string or valid local reference
#       And: 'AccessLogSettings.Format' is provided as a non-empty string
#      Then: PASS

#
# Constants
#
let API_GW_V2_STAGE_TYPE = "AWS::ApiGatewayV2::Stage"
let INPUT_DOCUMENT = this

#
# Assignments
#
let api_gateway_v2_stages = Resources.*[ Type == %API_GW_V2_STAGE_TYPE ]

#
# Primary Rules
#
rule api_gw_v2_access_logs_enabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                              %api_gateway_v2_stages not empty {
    check(%api_gateway_v2_stages.Properties)
        <<
        [CT.APIGATEWAY.PR.4]: Require an Amazon API Gateway V2 stage to have access logging activated
        [FIX]: Provide an 'AccessLogSettings' configuration, setting 'DestinationArn' to the ARN of an Amazon CloudWatch log group and 'Format' to a single line log format configuration.
        >>
}

rule api_gw_v2_access_logs_enabled_check when is_cfn_hook(%INPUT_DOCUMENT, %API_GW_V2_STAGE_TYPE) {
    check(%INPUT_DOCUMENT.%API_GW_V2_STAGE_TYPE.resourceProperties)
        <<
        [CT.APIGATEWAY.PR.4]: Require an Amazon API Gateway V2 stage to have access logging activated
        [FIX]: Provide an 'AccessLogSettings' configuration, setting 'DestinationArn' to the ARN of an Amazon CloudWatch log group and 'Format' to a single line log format configuration.
        >>
}

#
# Parameterized Rules
#
rule check(api_gateway_v2_stage) {
    %api_gateway_v2_stage {
        # Scenario 2
        AccessLogSettings exists
        AccessLogSettings is_struct

        AccessLogSettings {
            # Scenario 3
            DestinationArn exists
            check_is_string_and_not_empty(DestinationArn) or
            check_local_references(%INPUT_DOCUMENT, DestinationArn, "AWS::Logs::LogGroup")

            # Scenario 4, 5
            Format exists
            check_is_string_and_not_empty(Format)
        }
    }
}

#
# 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
    }
}