# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   step_functions_state_machine_logging_enabled_check
# 
# Description:
#   This control checks whether an AWS Step Functions state machine has logging enabled.
# 
# Reports on:
#   AWS::StepFunctions::StateMachine
# 
# 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 StepFunctions state machine resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a StepFunctions state machine resource
#       And: 'LoggingConfiguration' has not been provided
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a StepFunctions state machine resource
#       And: 'LoggingConfiguration' has been provided
#       And: In 'LoggingConfiguration', 'Level' has not been provided or provided and set to a value other than
#            'ERROR' or 'ALL'
#       And: In 'LoggingConfiguration', 'Destinations' has not been provided or provided as an empty list or list
#            containing empty strings or non-valid local references
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a StepFunctions state machine resource
#       And: 'LoggingConfiguration' has been provided
#       And: In 'LoggingConfiguration', 'Level' has not been provided or provided and set to a value other than
#            'ERROR' or 'ALL'
#       And: In 'LoggingConfiguration', 'Destinations' has not been provided or provided as an empty list or list
#            containing empty strings or non-valid local references
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a StepFunctions state machine resource
#       And: 'LoggingConfiguration' has been provided
#       And: In 'LoggingConfiguration', 'Level' has not been provided or provided and set to a value other than
#            'ERROR' or 'ALL'
#       And: In 'LoggingConfiguration', 'Destinations' has been provided as a list containing non-empty strings or
#            valid local references
#      Then: FAIL
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a StepFunctions state machine resource
#       And: 'LoggingConfiguration' has been provided
#       And: In 'LoggingConfiguration', 'Level' has been provided and set to 'ERROR' or 'ALL'
#       And: In 'LoggingConfiguration', 'Destinations' has been provided as a list containing non-empty strings or
#            valid local references
#      Then: PASS

#
# Constants
#
let STEP_FUNCTIONS_STATE_MACHINE_TYPE = "AWS::StepFunctions::StateMachine"
let ALLOWED_LOGGING_LEVELS = [ "ERROR", "ALL" ]
let INPUT_DOCUMENT = this

#
# Assignments
#
let step_functions_state_machines = Resources.*[ Type == %STEP_FUNCTIONS_STATE_MACHINE_TYPE ]

#
# Primary Rules
#
rule step_functions_state_machine_logging_enabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                                             %step_functions_state_machines not empty {
    check(%step_functions_state_machines.Properties)
        <<
        [CT.STEPFUNCTIONS.PR.1]: Require an AWS Step Functions state machine to have logging activated
        [FIX]: In 'LoggingConfiguration', set 'Level' to 'ERROR' or 'ALL', and set 'Destinations' to a list with one or more valid Amazon CloudWatch Logs log group ARNs.
        >>
}

rule step_functions_state_machine_logging_enabled_check when is_cfn_hook(%INPUT_DOCUMENT, %STEP_FUNCTIONS_STATE_MACHINE_TYPE) {
    check(%INPUT_DOCUMENT.%STEP_FUNCTIONS_STATE_MACHINE_TYPE.resourceProperties)
        <<
        [CT.STEPFUNCTIONS.PR.1]: Require an AWS Step Functions state machine to have logging activated
        [FIX]: In 'LoggingConfiguration', set 'Level' to 'ERROR' or 'ALL', and set 'Destinations' to a list with one or more valid Amazon CloudWatch Logs log group ARNs.
        >>
}

rule check(step_functions_state_machine) {
    %step_functions_state_machine {
        # Scenario 2
        LoggingConfiguration exists
        LoggingConfiguration is_struct

        LoggingConfiguration {
            # Scenarios 3, 4, 5 and 6
            Level exists
            Level in %ALLOWED_LOGGING_LEVELS

            Destinations exists
            Destinations is_list
            Destinations not empty

            Destinations[*] {
                CloudWatchLogsLogGroup exists
                CloudWatchLogsLogGroup is_struct

                CloudWatchLogsLogGroup {
                    LogGroupArn exists

                    check_is_string_and_not_empty(LogGroupArn) or
                    check_local_references(%INPUT_DOCUMENT, LogGroupArn, "AWS::Logs::LogGroup")
                }
            }
        }
    }
}

#
# 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/
    }
}

rule check_local_references(doc, reference_properties, referenced_resource_type) {
    %reference_properties {
        'Fn::GetAtt' {
            query_for_resource(%doc, this[0], %referenced_resource_type)
                <<Local Stack reference was invalid>>
        } or Ref {
            query_for_resource(%doc, this, %referenced_resource_type)
                <<Local Stack reference was invalid>>
        }
    }
}

rule query_for_resource(doc, resource_key, referenced_resource_type) {
    let referenced_resource = %doc.Resources[ keys == %resource_key ]
    %referenced_resource not empty
    %referenced_resource {
        Type == %referenced_resource_type
    }
}