# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   elasticache_auto_minor_version_upgrade_check
# 
# Description:
#   This control checks whether an Amazon ElastiCache for Redis cluster has automatic minor version upgrades enabled.
# 
# Reports on:
#   AWS::ElastiCache::CacheCluster
# 
# 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 cluster resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElastiCache cluster 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 cluster resource
#       And: 'Engine' has been provided and is set to 'redis'
#       And: 'EngineVersion' has been provided and set to a version less than 6
#      Then: SKIP
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElastiCache cluster resource
#       And: 'Engine' has been provided and is set to 'redis'
#       And: 'EngineVersion' has not been provided or 'EngineVersion' has been provided and set
#            to a version greater than or equal to 6
#       And: 'AutoMinorVersionUpgrade' has not been provided
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElastiCache cluster resource
#       And: 'Engine' has been provided and is set to 'redis'
#       And: 'EngineVersion' has not been provided or 'EngineVersion' has been provided and set
#            to a version greater than or equal to 6
#       And: 'AutoMinorVersionUpgrade' has been provided and set to a value other than bool(true)
#      Then: FAIL
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ElastiCache cluster resource
#       And: 'Engine' has been provided and is set to 'redis'
#       And: 'EngineVersion' has not been provided or 'EngineVersion' has been provided and set
#            to a version greater than or equal to 6
#       And: 'AutoMinorVersionUpgrade' has been provided and set to bool(true)
#      Then: PASS

#
# Constants
#
let ELASTICACHE_CLUSTER_TYPE = "AWS::ElastiCache::CacheCluster"
let INPUT_DOCUMENT = this
let REDIS_ENGINE_TYPE = "redis"
let UNSUPPORTED_REDIS_ENGINE_VERSIONS_FOR_AUTO_UPGRADE = [
    /^2\./,
    /^3\./,
    /^4\./,
    /^5\./
]

#
# Assignments
#
let elasticache_clusters = Resources.*[ Type == %ELASTICACHE_CLUSTER_TYPE ]

#
# Primary Rules
#
rule elasticache_auto_minor_version_upgrade_check when is_cfn_template(%INPUT_DOCUMENT)
                                                       %elasticache_clusters not empty {
    check(%elasticache_clusters.Properties)
        <<
        [CT.ELASTICACHE.PR.2]: Require an Amazon ElastiCache for Redis cluster to have automatic minor version upgrades activated
        [FIX]: Set the value of the 'AutoMinorVersionUpgrade' parameter to true.
        >>
}

rule elasticache_auto_minor_version_upgrade_check when is_cfn_hook(%INPUT_DOCUMENT, %ELASTICACHE_CLUSTER_TYPE) {
    check(%INPUT_DOCUMENT.%ELASTICACHE_CLUSTER_TYPE.resourceProperties)
        <<
        [CT.ELASTICACHE.PR.2]: Require an Amazon ElastiCache for Redis cluster to have automatic minor version upgrades activated
        [FIX]: Set the value of the 'AutoMinorVersionUpgrade' parameter to true.
        >>
}

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

        # Scenario 3
        EngineVersion not exists or
        EngineVersion not in %UNSUPPORTED_REDIS_ENGINE_VERSIONS_FOR_AUTO_UPGRADE
    ] {
        # Scenario 4, 5 and 6
        AutoMinorVersionUpgrade exists
        AutoMinorVersionUpgrade == 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
}