# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   elasticache_repl_grp_redis_auth_enabled_check
# 
# Description:
#   This control checks whether an Amazon ElastiCache replication group with an engine version earlier than 6.0 has Redis AUTH enabled.
# 
# Reports on:
#   AWS::ElastiCache::ReplicationGroup
# 
# 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 ElastiCache replication group resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElastiCache replication group resource
#       And: 'Engine' has not been provided or has been provided and is not set to 'redis'
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElastiCache replication group resource
#       And: 'Engine' has been provided and is set to 'redis'
#       And: 'EngineVersion' has not been provided or has been provided and set to a version greater than or equal to 6
#      Then: SKIP
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElastiCache replication group resource
#       And: 'Engine' has been provided and is set to 'redis'
#       And: 'EngineVersion' has been provided and set to a version less than 6
#       And: 'AuthToken' has not been provided or has been provided and set to an empty string
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElastiCache replication group resource
#       And: 'Engine' has been provided and is set to 'redis'
#       And: 'EngineVersion' has been provided and set to a version less than 6
#       And: 'AuthToken' has been provided and set to a non-empty string
#      Then: PASS

#
# Constants
#
let ELASTICACHE_REPLICATION_GROUP_TYPE = "AWS::ElastiCache::ReplicationGroup"
let REDIS_ENGINE_TYPE = "redis"
let SUPPORTED_REDIS_ENGINE_VERSIONS_FOR_REDIS_AUTH = [
    /^2\./,
    /^3\./,
    /^4\./,
    /^5\./
]
let INPUT_DOCUMENT = this

#
# Assignments
#
let elasticache_replication_groups = Resources.*[ Type == %ELASTICACHE_REPLICATION_GROUP_TYPE ]

#
# Primary Rules
#
rule elasticache_repl_grp_redis_auth_enabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                                        %elasticache_replication_groups not empty {
    check(%elasticache_replication_groups.Properties)
        <<
        [CT.ELASTICACHE.PR.7]: Require an Amazon ElastiCache replication group of earlier Redis versions to have Redis AUTH activated
        [FIX]: Set the value of the 'AuthToken' parameter to a string between 16 characters and 128 characters in length, which contains only printable ASCII characters and does not contain non-alphanumeric characters outside of the set (!, &,
        >>
}

rule elasticache_repl_grp_redis_auth_enabled_check when is_cfn_hook(%INPUT_DOCUMENT, %ELASTICACHE_REPLICATION_GROUP_TYPE) {
    check(%INPUT_DOCUMENT.%ELASTICACHE_REPLICATION_GROUP_TYPE.resourceProperties)
        <<
        [CT.ELASTICACHE.PR.7]: Require an Amazon ElastiCache replication group of earlier Redis versions to have Redis AUTH activated
        [FIX]: Set the value of the 'AuthToken' parameter to a string between 16 characters and 128 characters in length, which contains only printable ASCII characters and does not contain non-alphanumeric characters outside of the set (!, &,
        >>
}

#
# Parameterized Rules
#
rule check(elasticache_replication_group) {
    %elasticache_replication_group [
        # Scenario 2
        Engine exists
        Engine == %REDIS_ENGINE_TYPE

        # Scenario 3
        EngineVersion exists
        EngineVersion in %SUPPORTED_REDIS_ENGINE_VERSIONS_FOR_REDIS_AUTH
    ] {
        # Scenarios 4 and 5
        AuthToken exists
        check_is_string_and_not_empty(AuthToken)
    }
}

#
# 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/
    }
}