# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   kinesis_stream_encrypted_check
# 
# Description:
#   This control checks whether Amazon Kinesis data streams are encrypted at rest with server-side encryption.
# 
# Reports on:
#   AWS::Kinesis::Stream
# 
# 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 Kinesis stream resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Kinesis stream resource
#       And: 'StreamEncryption' 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 Kinesis stream resource
#       And: 'StreamEncryption' has been provided
#       And: 'StreamEncryption.EncryptionType' has not been provided or provided as an empty string
#       And: 'StreamEncryption.KeyId' has not been provided or provided as an empty string or invalid local reference
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Kinesis stream resource
#       And: 'StreamEncryption' has been provided
#       And: 'StreamEncryption.EncryptionType' has been provided as a non-empty string
#       And: 'StreamEncryption.KeyId' has not been provided or provided as an empty string or invalid local reference
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Kinesis stream resource
#       And: 'StreamEncryption' has been provided
#       And: 'StreamEncryption.EncryptionType' has not been provided or provided as an empty string
#       And: 'StreamEncryption.KeyId' has been provided as a non-empty string or valid local reference
#      Then: FAIL
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Kinesis stream resource
#       And: 'StreamEncryption' has been provided
#       And: 'StreamEncryption.EncryptionType' has been provided as a non-empty string
#       And: 'StreamEncryption.KeyId' has been provided as a non-empty string or valid local reference
#      Then: PASS

#
# Constants
#
let KINESIS_STREAM_TYPE = "AWS::Kinesis::Stream"
let INPUT_DOCUMENT = this

#
# Assignments
#
let kinesis_streams = Resources.*[ Type == %KINESIS_STREAM_TYPE ]

#
# Primary Rules
#
rule kinesis_stream_encrypted_check when is_cfn_template(%INPUT_DOCUMENT)
                                         %kinesis_streams not empty {
    check(%kinesis_streams.Properties)
        <<
        [CT.KINESIS.PR.1]: Require any Amazon Kinesis data stream to have encryption at rest configured
        [FIX]: Specify a 'StreamEncryption' configuration, with 'EncryptionType' set to 'KMS' and 'KeyId' set to an AWS KMS key identifier.
        >>
}

rule kinesis_stream_encrypted_check when is_cfn_hook(%INPUT_DOCUMENT, %KINESIS_STREAM_TYPE) {
    check(%INPUT_DOCUMENT.%KINESIS_STREAM_TYPE.resourceProperties)
        <<
        [CT.KINESIS.PR.1]: Require any Amazon Kinesis data stream to have encryption at rest configured
        [FIX]: Specify a 'StreamEncryption' configuration, with 'EncryptionType' set to 'KMS' and 'KeyId' set to an AWS KMS key identifier.
        >>
}

#
# Parameterized Rules
#
rule check(kinesis_stream) {
    %kinesis_stream {
        # Scenario 2
        StreamEncryption exists
        StreamEncryption is_struct

        StreamEncryption {
            # Scenario 3
            EncryptionType exists
            KeyId exists

            # Scenario 4, 5 and 6
            check_is_string_and_not_empty(EncryptionType)
            check_is_string_and_not_empty(KeyId) or
            check_local_references(%INPUT_DOCUMENT, KeyId, "AWS::KMS::Key") or
            check_local_references(%INPUT_DOCUMENT, KeyId, "AWS::KMS::Alias")
        }
    }
}

#
# 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
    }
}