# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   s3_bucket_logging_enabled_check
# 
# Description:
#   This control checks whether server access logging is enabled for 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: 'LoggingConfiguration' 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: 'LoggingConfiguration' has been provided
#       And: 'LoggingConfiguration.DestinationBucketName' has been provided with an empty string or non-valid local
#            reference
#      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: 'LoggingConfiguration' has been provided
#      Then: PASS
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Amazon S3 bucket resource
#       And: 'LoggingConfiguration' has been provided
#       And: 'LoggingConfiguration.DestinationBucketName' has been provided with a non-empty string or valid local
#            reference
#      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_bucket_logging_enabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                          %s3_buckets not empty {
    check(%s3_buckets.Properties)
        <<
        [CT.S3.PR.2]: Require an Amazon S3 bucket to have server access logging configured
        [FIX]: Set a 'LoggingConfiguration' on the S3 Bucket and optionally set 'DestinationBucketName' to an S3 bucket configured to receive S3 Access Logs.
        >>
}

rule s3_bucket_logging_enabled_check when is_cfn_hook(%INPUT_DOCUMENT, %S3_BUCKET_TYPE) {
    check(%INPUT_DOCUMENT.%S3_BUCKET_TYPE.resourceProperties)
        <<
        [CT.S3.PR.2]: Require an Amazon S3 bucket to have server access logging configured
        [FIX]: Set a 'LoggingConfiguration' on the S3 Bucket and optionally set 'DestinationBucketName' to an S3 bucket configured to receive S3 Access Logs.
        >>
}

#
# Parameterized Rules
#
rule check(s3_bucket) {
    %s3_bucket {
        # Scenario 2 and 4
        LoggingConfiguration exists
        LoggingConfiguration is_struct

        LoggingConfiguration {
            when DestinationBucketName exists {
                # Scenario 3, 4 and 5
                check_is_string_and_not_empty(DestinationBucketName) or
                check_local_references(%INPUT_DOCUMENT, DestinationBucketName, %S3_BUCKET_TYPE)
            }
        }
    }
}


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

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_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
    }
}