# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   ecs_awsvpc_networking_enabled_check
# 
# Description:
#   This control checks whether the networking mode for Amazon Elastic Container Service (ECS) task definitions is set to 'awsvpc'.
# 
# Reports on:
#   AWS::ECS::TaskDefinition
# 
# 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 task definition 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 task definition resource
#       And: 'RequiresCompatibilities' is present and only has one entry in the list set to 'EXTERNAL'
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document contains an ECS task definition resource
#       And: 'RequiresCompatibilities' is either not present or set to a list with entries that include 'EC2',
#            'FARGATE' or both.
#       And: 'NetworkMode' is not present
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document contains an ECS task definition resource
#       And: 'RequiresCompatibilities' is either not present or set to a list with entries that include 'EC2',
#            'FARGATE' or both.
#       And: 'NetworkMode' is present
#       And: 'NetworkMode' is not set to 'awsvpc'
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document contains an ECS task definition resource
#       And: 'RequiresCompatibilities' is either not present or set to a list with entries that include 'EC2',
#            'FARGATE' or both.
#       And: 'NetworkMode' is present
#       And: 'NetworkMode' is set to 'awsvpc'
#      Then: PASS

#
# Constants
#
let ECS_TASK_DEFINITION_TYPE = "AWS::ECS::TaskDefinition"
let ALLOWED_NETWORK_MODES = [ "awsvpc" ]
let SUPPORTED_LAUNCH_PLATFORMS = [ "EC2" , "FARGATE" ]
let INPUT_DOCUMENT = this

#
# Assignments
#
let ecs_task_definitions = Resources.*[ Type == %ECS_TASK_DEFINITION_TYPE ]

#
# Primary Rules
#
rule ecs_awsvpc_networking_enabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                              %ecs_task_definitions not empty {
    check(%ecs_task_definitions.Properties)
        <<
        [CT.ECS.PR.4]: Require Amazon ECS tasks to use 'awsvpc' networking mode
        [FIX]: Set 'NetworkMode' to 'awsvpc' for Amazon ECS tasks that deploy to Amazon EC2 or AWS Fargate.
        >>
}

rule ecs_awsvpc_networking_enabled_check when is_cfn_hook(%INPUT_DOCUMENT, %ECS_TASK_DEFINITION_TYPE) {
    check(%INPUT_DOCUMENT.%ECS_TASK_DEFINITION_TYPE.resourceProperties)
        <<
        [CT.ECS.PR.4]: Require Amazon ECS tasks to use 'awsvpc' networking mode
        [FIX]: Set 'NetworkMode' to 'awsvpc' for Amazon ECS tasks that deploy to Amazon EC2 or AWS Fargate.
        >>
}

#
# Parameterized Rules
#
rule check(ecs_task_definition) {
    %ecs_task_definition [ filter_external_task_definitions(this) ] {
        # Scenario 3
        NetworkMode exists

        # Scenario 4 and 5
        NetworkMode is_string
        NetworkMode in %ALLOWED_NETWORK_MODES
    }
}

rule filter_external_task_definitions(ecs_task_definition) {
    %ecs_task_definition {
        # Scenario 2
        RequiresCompatibilities not exists or
        filter_supported_task_definitions(RequiresCompatibilities)
    }
}

rule filter_supported_task_definitions(requires_compatibilities) {
    %requires_compatibilities {
        this is_list
        this not empty
        some this[*] in %SUPPORTED_LAUNCH_PLATFORMS
    }
}

#
# 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
}