# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   s3_bucket_level_public_access_prohibited_check
# 
# Description:
#   This control checks whether your Amazon Simple Storage Service (Amazon S3) bucket has a bucket-level Block Public Access (BPA) configuration.
# 
# 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: 'PublicAccessBlockConfiguration' 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: 'PublicAccessBlockConfiguration' has been provided
#       And: 'BlockPublicAcls' or 'BlockPublicPolicy' or 'IgnorePublicAcls' or 'RestrictPublicBuckets'
#            have 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 Amazon S3 bucket Resource
#       And: 'PublicAccessBlockConfiguration' has been provided
#       And: Any of 'BlockPublicAcls' or 'BlockPublicPolicy' or 'IgnorePublicAcls' or 'RestrictPublicBuckets'
#            have been set to a value other than bool(true) (e.g. bool(false), str(false), other)
#      Then: FAIL
#   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: 'PublicAccessBlockConfiguration' has been provided
#       And: 'BlockPublicAcls' or 'BlockPublicPolicy' or 'IgnorePublicAcls' or 'RestrictPublicBuckets'
#            have all been set to bool(true)
#      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_level_public_access_prohibited_check when is_cfn_template(%INPUT_DOCUMENT)
                                                         %s3_buckets not empty {
    check(%s3_buckets.Properties)
        <<
        [CT.S3.PR.1]: Require an Amazon S3 bucket to have block public access settings configured
        [FIX]: The parameters 'BlockPublicAcls', 'BlockPublicPolicy', 'IgnorePublicAcls', 'RestrictPublicBuckets' must be set to true under the bucket-level 'PublicAccessBlockConfiguration'.
        >>
}

rule s3_bucket_level_public_access_prohibited_check when is_cfn_hook(%INPUT_DOCUMENT, %S3_BUCKET_TYPE) {
    check(%INPUT_DOCUMENT.%S3_BUCKET_TYPE.resourceProperties)
        <<
        [CT.S3.PR.1]: Require an Amazon S3 bucket to have block public access settings configured
        [FIX]: The parameters 'BlockPublicAcls', 'BlockPublicPolicy', 'IgnorePublicAcls', 'RestrictPublicBuckets' must be set to true under the bucket-level 'PublicAccessBlockConfiguration'.
        >>
}

#
# Parameterized Rules
#
rule check(s3_bucket) {
    %s3_bucket {
        # Scenario 2
        PublicAccessBlockConfiguration exists
        PublicAccessBlockConfiguration is_struct

        PublicAccessBlockConfiguration {
            # Scenario 3
            BlockPublicAcls exists
            BlockPublicPolicy exists
            IgnorePublicAcls exists
            RestrictPublicBuckets exists

            # Scenarios 4 and 5
            BlockPublicAcls == true
            BlockPublicPolicy == true
            IgnorePublicAcls == true
            RestrictPublicBuckets == true
        }
    }
}

#
# 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
}