# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   cloudfront_default_root_object_configured_check
# 
# Description:
#   This control checks whether an Amazon CloudFront distribution is configured to return a specific object that is the default root object.
# 
# Reports on:
#    AWS::CloudFront::Distribution
# 
# 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 CloudFront distribution resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a CloudFront distribution resource
#       And: 'DefaultRootObject' is not present on the CloudFront distribution resource or is present and
#            is an empty string
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a CloudFront distribution resource
#       And: 'DefaultRootObject' is present on the CloudFront distribution resource and is a non-empty string
#      Then: PASS

#
# Constants
#
let CLOUDFRONT_DISTRIBUTION_TYPE = "AWS::CloudFront::Distribution"
let INPUT_DOCUMENT = this

#
# Assignments
#
let cloudfront_distributions = Resources.*[ Type == %CLOUDFRONT_DISTRIBUTION_TYPE ]

#
# Primary Rules
#
rule cloudfront_default_root_object_configured_check when is_cfn_template(%INPUT_DOCUMENT)
                                                          %cloudfront_distributions not empty {
    check(%cloudfront_distributions.Properties)
        <<
        [CT.CLOUDFRONT.PR.1]: Require an Amazon CloudFront distribution to have a default root object configured
        [FIX]: Specify a default root object in the 'DefaultRootObject' property.
        >>
}

rule cloudfront_default_root_object_configured_check when is_cfn_hook(%INPUT_DOCUMENT, %CLOUDFRONT_DISTRIBUTION_TYPE) {
    check(%INPUT_DOCUMENT.%CLOUDFRONT_DISTRIBUTION_TYPE.resourceProperties)
        <<
        [CT.CLOUDFRONT.PR.1]: Require an Amazon CloudFront distribution to have a default root object configured
        [FIX]: Specify a default root object in the 'DefaultRootObject' property.
        >>
}

#
# Parameterized Rules
#
rule check(cloudfront_distribution) {
    %cloudfront_distribution {
        DistributionConfig exists
        DistributionConfig is_struct

        DistributionConfig {
            # Scenario 2
            DefaultRootObject exists
            # Scenario 3
            check_is_string_and_not_empty(DefaultRootObject)
        }
    }
}

#
# 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
}