# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   autoscaling_launch_config_hop_limit_check
# 
# Description:
#   This control checks whether an Amazon EC2 Auto Scaling launch configuration has a metadata token hop limit set to '1'.
# 
# Reports on:
#   AWS::AutoScaling::LaunchConfiguration
# 
# 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 Auto Scaling launch configuration resources
#       Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains Auto Scaling launch configuration resources
#       And: 'MetadataOptions' has been provided
#       And: 'MetadataOptions.HttpEndpoint' has been provided is equal to 'disabled'
#       Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains Auto Scaling launch configuration resources
#       And: 'MetadataOptions' has been provided
#       And: 'MetadataOptions.HttpEndpoint' has not been provided or has been provided and is equal to 'enabled'
#       And: 'MetadataOptions.HttpPutResponseHopLimit' has been provided but is not equal to an integer of 1
#       Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains Auto Scaling launch configuration resources
#       And: 'MetadataOptions' has not been provided
#       Then: PASS
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains Auto Scaling launch configuration resources
#       And: 'MetadataOptions' has been provided
#       And: 'MetadataOptions.HttpEndpoint' has not been provided or has been provided and is equal to 'enabled'
#       And: 'MetadataOptions.HttpPutResponseHopLimit' has not been provided
#       Then: PASS
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains Auto Scaling launch configuration resources
#       And: 'MetadataOptions' has been provided
#       And: 'MetadataOptions.HttpEndpoint' has not been provided or has been provided and is equal to 'enabled'
#       And: 'MetadataOptions.HttpPutResponseHopLimit' has been provided and is equal to an integer of 1
#       Then: PASS

#
# Constants
#
let AUTOSCALING_LAUNCH_CONFIG_TYPE = "AWS::AutoScaling::LaunchConfiguration"
let INPUT_DOCUMENT = this

#
# Assignments
#
let autoscaling_launch_configurations = Resources.*[ Type == %AUTOSCALING_LAUNCH_CONFIG_TYPE]

#
# Primary Rules
#
rule autoscaling_launch_config_hop_limit_check when is_cfn_template(this)
                                                    %autoscaling_launch_configurations not empty {
    check(%autoscaling_launch_configurations.Properties)
        <<
        [CT.AUTOSCALING.PR.3]: Require an Amazon EC2 Auto Scaling launch configuration to have a single-hop metadata response limit
        [FIX]: Provide a 'MetadataOptions' configuration with 'HttpPutResponseLimit' set to '1', or omit the 'HttpPutResponseLimit' property to adopt the AWS CloudFormation default value of '1'.
        >>
}

rule autoscaling_launch_config_hop_limit_check when is_cfn_hook(%INPUT_DOCUMENT, %AUTOSCALING_LAUNCH_CONFIG_TYPE) {
    check(%INPUT_DOCUMENT.%AUTOSCALING_LAUNCH_CONFIG_TYPE.resourceProperties)
        <<
        [CT.AUTOSCALING.PR.3]: Require an Amazon EC2 Auto Scaling launch configuration to have a single-hop metadata response limit
        [FIX]: Provide a 'MetadataOptions' configuration with 'HttpPutResponseLimit' set to '1', or omit the 'HttpPutResponseLimit' property to adopt the AWS CloudFormation default value of '1'.
        >>
}

#
# Parameterized Rules
#
rule check(autoscaling_launch_configurations) {
    %autoscaling_launch_configurations [
        # Scenarios 2, 3 and 4
        filter_launch_configuration(this)
    ] {
        # Scenarios 5 and 6
        MetadataOptions not exists or
        MetadataOptions {
            HttpPutResponseHopLimit not exists or
            HttpPutResponseHopLimit == 1
        }
    }
}

rule filter_launch_configuration(autoscaling_launch_configurations) {
    %autoscaling_launch_configurations {
        MetadataOptions not exists or
        filter_metadata_options_provided(this)
    }
}

rule filter_metadata_options_provided(options) {
    %options {
        MetadataOptions is_struct
        MetadataOptions {
            HttpEndpoint not exists or
            HttpEndpoint == "enabled"
        }
    }
}

#
# 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
}