# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#    sqs_queue_encrypted_check
# 
# Description:
#   This control checks whether an Amazon SQS queue is encrypted at rest.
# 
# Reports on:
#    AWS::SQS::Queue
# 
# 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 SQS queue resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'KmsMasterKeyId' or 'SqsManagedSseEnabled' have not been provided on the SQS queue resource
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'KmsMasterKeyId' has not been provided
#       And: 'SqsManagedSseEnabled' has been provided and set to bool(false)
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'KmsMasterKeyId' has been provided as an empty string or invalid local reference to a KMS key or alias
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'SqsManagedSseEnabled' is not provided or set to bool(false)
#       And: 'KmsMasterKeyId' is provided as a non-empty string or local reference to a KMS key
#      Then: PASS
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'KmsMasterKeyId' is not provided
#       And: 'SqsManagedSseEnabled' is provided and set to bool(true)
#      Then: PASS

#
# Constants
#
let SQS_QUEUE_TYPE = "AWS::SQS::Queue"
let INPUT_DOCUMENT = this
#
# Assignments
#
let sqs_queues = Resources.*[ Type == %SQS_QUEUE_TYPE ]

#
# Primary Rules
#
rule sqs_queue_encrypted_check when is_cfn_template(%INPUT_DOCUMENT)
                                    %sqs_queues not empty {
    check(%sqs_queues.Properties)
        <<
        [CT.SQS.PR.2]: Require any Amazon SQS queue to have encryption at rest configured
        [FIX]: Set 'SqsManagedSseEnabled' to 'true' or set an AWS KMS key identifier in the 'KmsMasterKeyId' property.
        >>
}

rule sqs_queue_encrypted_check when is_cfn_hook(%INPUT_DOCUMENT, %SQS_QUEUE_TYPE) {
    check(%INPUT_DOCUMENT.%SQS_QUEUE_TYPE.resourceProperties)
        <<
        [CT.SQS.PR.2]: Require any Amazon SQS queue to have encryption at rest configured
        [FIX]: Set 'SqsManagedSseEnabled' to 'true' or set an AWS KMS key identifier in the 'KmsMasterKeyId' property.
        >>
}

#
# Parameterized Rules
#
rule check(sqs_queue) {
    %sqs_queue{
        check_sse_enabled(this) or
        check_kms_valid(this)
    }
}

rule check_sse_enabled(sqs_queue) {
    # Scenario 2
    SqsManagedSseEnabled exists

    # Scenario 3, 6
    KmsMasterKeyId not exists
    SqsManagedSseEnabled == true
}

rule check_kms_valid(sqs_queue) {
    # Scenario 2
    KmsMasterKeyId exists

    # Scenario 4, 5
    check_is_string_and_not_empty(KmsMasterKeyId) or
    check_local_references(%INPUT_DOCUMENT, KmsMasterKeyId, "AWS::KMS::Key") or
    check_local_references(%INPUT_DOCUMENT, KmsMasterKeyId, "AWS::KMS::Alias")

    # Scenario 5
    SqsManagedSseEnabled not exists or
    SqsManagedSseEnabled == false
}

#
# 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
    }
}