# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   ecs_task_definition_pid_mode_check
# 
# Description:
#   This control checks whether Amazon Elastic Container Service (ECS) task definitions are configured to share a host's process namespace with its containers.
# 
# 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 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 or CloudFormation hook document
#       And: The input document contains an ECS task definition resource
#       And: 'PidMode' is provided as an empty string
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ECS task definition resource
#       And: 'PidMode' is set to 'host'
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ECS task definition resource
#       And: 'PidMode' is not present
#      Then: PASS
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an ECS task definition resource
#       And: 'PidMode' is provided as a non-empty string that is not 'host'
#      Then: PASS

#
# Constants
#
let ECS_TASK_DEFINITION_TYPE = "AWS::ECS::TaskDefinition"
let INPUT_DOCUMENT = this

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

#
# Primary Rules
#
rule ecs_task_definition_pid_mode_check when is_cfn_template(%INPUT_DOCUMENT)
                                             %ecs_task_definitions not empty {
    check(%ecs_task_definitions.Properties)
        <<
        [CT.ECS.PR.10]: Require that Amazon ECS task definitions do not share the host's process namespace
        [FIX]: Omit the 'PidMode' property, or set 'PidMode' to 'task'.
        >>
}

rule ecs_task_definition_pid_mode_check when is_cfn_hook(%INPUT_DOCUMENT, %ECS_TASK_DEFINITION_TYPE) {
    check(%INPUT_DOCUMENT.%ECS_TASK_DEFINITION_TYPE.resourceProperties)
        <<
        [CT.ECS.PR.10]: Require that Amazon ECS task definitions do not share the host's process namespace
        [FIX]: Omit the 'PidMode' property, or set 'PidMode' to 'task'.
        >>
}

#
# Parameterized Rules
#
rule check(ecs_task_definition) {
    %ecs_task_definition {
        # Scenario 2
        PidMode not exists or

        # Scenario 3 and 4
        check_pidmode_value(PidMode)
    }
}

rule check_pidmode_value(pid_mode) {
    %pid_mode {
        check_is_string_and_not_empty(this)
        this != "host"
    }
}

#
# 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/
    }
}