# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   ecs_fargate_latest_platform_version_check
# 
# Description:
#   This control checks whether Amazon ECS Fargate services are configured to deploy using the 'LATEST' platform version rather than a specified version number.
# 
# Reports on:
#   AWS::ECS::Service
# 
# Evaluates:
#   AWS CloudFormation, AWS CloudFormation hook
# 
# Rule Parameters:
#   None
# 
# Scenarios:
#   Scenario: 1
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document does not contain an ECS service resource
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document contains an ECS service resource
#       And: 'LaunchType' is not present
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document contains an ECS service resource
#       And: 'LaunchType' is present and not set to 'FARGATE'
#      Then: SKIP
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document contains an ECS service resource
#       And: 'LaunchType' is present and set to 'FARGATE'
#       And: 'PlatformVersion' is present and not set to 'LATEST'
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document contains an ECS service resource
#       And: 'LaunchType' is present and set to 'FARGATE'
#       And: 'PlatformVersion' is not present
#      Then: PASS
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document contains an ECS service resource
#       And: 'LaunchType' is present and set to 'FARGATE'
#       And: 'PlatformVersion' is set to 'LATEST'
#      Then: PASS

#
# Constants
#
let ECS_SERVICE_TYPE = "AWS::ECS::Service"
let INPUT_DOCUMENT = this

#
# Assignments
#
let ecs_services = Resources.*[ Type == %ECS_SERVICE_TYPE ]

#
# Primary Rules
#
rule ecs_fargate_latest_platform_version_check when is_cfn_template(%INPUT_DOCUMENT)
                                                    %ecs_services not empty {
    check(%ecs_services.Properties)
        <<
        [CT.ECS.PR.1]: Require AWS ECS Fargate Services to run on the latest Fargate platform version
        [FIX]: When 'LaunchType' is set to 'FARGATE', set the 'PlatformVersion' property to 'LATEST' or omit the 'PlatformVersion' property (default: 'LATEST').
        >>
}

rule ecs_fargate_latest_platform_version_check when is_cfn_hook(%INPUT_DOCUMENT, %ECS_SERVICE_TYPE) {
    check(%INPUT_DOCUMENT.%ECS_SERVICE_TYPE.resourceProperties)
        <<
        [CT.ECS.PR.1]: Require AWS ECS Fargate Services to run on the latest Fargate platform version
        [FIX]: When 'LaunchType' is set to 'FARGATE', set the 'PlatformVersion' property to 'LATEST' or omit the 'PlatformVersion' property (default: 'LATEST').
        >>
}

#
# Parameterized Rules
#
rule check(ecs_service) {
    %ecs_service [ filter_launch_type_is_fargate(this) ]{
        # Scenario 5
        PlatformVersion not exists  or

        # Scenario 4 and 6
        check_fargate_version_latest(PlatformVersion)
    }
}

rule filter_launch_type_is_fargate(ecs_service) {
    %ecs_service {
        # Scenario 2
        LaunchType exists
        LaunchType is_string

        # Scenario 3
        LaunchType == "FARGATE"
    }
}

rule check_fargate_version_latest(property) {
    %property {
        this is_string
        this == "LATEST"
    }
}

#
# 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
}