# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   autoscaling_mixed_instances_policy_multiple_instance_types_check
# 
# Description:
#   This control checks whether an Amazon EC2 Auto Scaling group uses multiple instance types, by means of a mixed instance policy and explicit instance type overrides.
# 
# Reports on:
#   AWS::AutoScaling::AutoscalingGroup
# 
# 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 Group resources
#      Then: SKIP
#  Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains Auto Scaling Group resources
#       And: 'MixedInstancesPolicy.LaunchTemplate.Overrides' has been provided as a list
#       And: There exists any 'Overrides' entry where 'InstanceRequirements' is present
#       And: There exists no 'Overrides' entry where 'InstanceType' is present
#      Then: SKIP
#  Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains Auto Scaling Group resources
#       And: 'MixedInstancesPolicy.LaunchTemplate.LaunchTemplateSpecification' has been provided
#       And: 'MixedInstancesPolicy.LaunchTemplate.Overrides' has not been provided
#      Then: FAIL
#  Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains Auto Scaling Group resources
#       And: 'MixedInstancesPolicy.LaunchTemplate.LaunchTemplateSpecification' has been provided
#       And: 'MixedInstancesPolicy.LaunchTemplate.Overrides' has been provided as a list
#       And: 'InstanceType' is not present or is present as an empty string in 'MixedInstancesPolicy.LaunchTemplate.Overrides'
#      Then: FAIL
#  Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains Auto Scaling Group resources
#       And: 'MixedInstancesPolicy.LaunchTemplate.LaunchTemplateSpecification' has been provided
#       And: 'MixedInstancesPolicy.LaunchTemplate.Overrides' has been provided as a list
#       And: There exists any 'Overrides' entry where 'InstanceRequirements' is present
#       And: There exists any 'Overrides' entry where 'InstanceType' is present
#      Then: FAIL
#  Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains Auto Scaling Group resources
#       And: 'MixedInstancesPolicy.LaunchTemplate.LaunchTemplateSpecification' has been provided
#       And: 'MixedInstancesPolicy.LaunchTemplate.Overrides' has been provided as a list
#       And: 'InstanceType' is present in 'MixedInstancesPolicy.LaunchTemplate.Overrides' as a non-empty string
#       And: Length of 'MixedInstancesPolicy.LaunchTemplate.Overrides' is less than or equal to 1
#      Then: FAIL
#  Scenario: 7
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains Auto Scaling Group resources
#       And: 'MixedInstancesPolicy.LaunchTemplate.LaunchTemplateSpecification' has been provided
#       And: 'MixedInstancesPolicy.LaunchTemplate.Overrides' has been provided as a list
#       And: 'InstanceType' is present in 'MixedInstancesPolicy.LaunchTemplate.Overrides' as a non-empty string
#       And: Length of 'MixedInstancesPolicy.LaunchTemplate.Overrides' is greater than 1
#      Then: PASS

#
# Constants
#
let AUTOSCALING_GROUP_TYPE = "AWS::AutoScaling::AutoScalingGroup"
let INPUT_DOCUMENT = this

#
# Assignments
#
let autoscaling_groups = Resources.*[ Type == %AUTOSCALING_GROUP_TYPE ]

#
# Primary Rules
#
rule autoscaling_mixed_instances_policy_multiple_instance_types_check when is_cfn_template(%INPUT_DOCUMENT)
                                                                           %autoscaling_groups not empty {
    check(%autoscaling_groups.Properties)
        <<
        [CT.AUTOSCALING.PR.6]: Require any Amazon EC2 Auto Scaling groups to use multiple instance types
        [FIX]: Within a 'MixedInstancePolicy' configuration, provide a 'LaunchTemplate' configuration with two entries in the 'Overrides' property. Within each override, set the 'InstanceType' property to a different Amazon EC2 instance type.
        >>
}

rule autoscaling_mixed_instances_policy_multiple_instance_types_check when is_cfn_hook(%INPUT_DOCUMENT, %AUTOSCALING_GROUP_TYPE) {
    check(%INPUT_DOCUMENT.%AUTOSCALING_GROUP_TYPE.resourceProperties)
        <<
        [CT.AUTOSCALING.PR.6]: Require any Amazon EC2 Auto Scaling groups to use multiple instance types
        [FIX]: Within a 'MixedInstancePolicy' configuration, provide a 'LaunchTemplate' configuration with two entries in the 'Overrides' property. Within each override, set the 'InstanceType' property to a different Amazon EC2 instance type.
        >>
}

#
# Parameterized Rules
#
rule check(autoscaling_group) {
    %autoscaling_group [
        # Scenario 2
        filter_asg_no_instance_requirement_overrides(this)
    ] {
        # Scenario 4, 5, 6
        MixedInstancesPolicy exists
        MixedInstancesPolicy is_struct

        MixedInstancesPolicy {
            LaunchTemplate exists
            LaunchTemplate is_struct

            LaunchTemplate {
                LaunchTemplateSpecification exists
                LaunchTemplateSpecification is_struct

                Overrides exists
                Overrides is_list
                Overrides not empty

                Overrides[0] exists
                Overrides[1] exists

                Overrides[*] {
                    InstanceType exists
                    check_is_string_and_not_empty(InstanceType)
                }

                Overrides[0].InstanceType not in Overrides[1].InstanceType
            }
        }
    }

    %autoscaling_group [
        # Scenario 2
        filter_asg_conflicting_overrides(this)
    ] {
        MixedInstancesPolicy {
            LaunchTemplate {
                Overrides[*] {
                    check_mutually_exclusive_property_combination(InstanceType, InstanceRequirements) or
                    check_mutually_exclusive_property_combination(InstanceRequirements, InstanceType)
                }
            }
        }
    }
}

rule filter_asg_no_instance_requirement_overrides(autoscaling_group) {
    %autoscaling_group {
        MixedInstancesPolicy not exists or
        filter_mixed_instances_policy_no_instance_requirement_overrides(this)
    }
}

rule filter_mixed_instances_policy_no_instance_requirement_overrides(autoscaling_group) {
    %autoscaling_group {
        MixedInstancesPolicy is_struct
        MixedInstancesPolicy {
            LaunchTemplate not exists or
            filter_launch_templates_no_instance_requirement_overrides(this)
        }
    }
}

rule filter_launch_templates_no_instance_requirement_overrides(launch_template) {
    %launch_template {
        LaunchTemplate is_struct
        LaunchTemplate {
            Overrides not exists or
            filter_overrides_no_instance_requirement_overrides(this)
        }
    }
}

rule filter_overrides_no_instance_requirement_overrides(overrides) {
    %overrides {
        Overrides is_list
        Overrides empty or
        Overrides[*] {
            InstanceRequirements not exists
        }
    }
}

rule filter_asg_conflicting_overrides(autoscaling_group) {
    %autoscaling_group {
        MixedInstancesPolicy not exists or
        filter_mixed_instances_policy_conflicting_overrides(this)
    }
}

rule filter_mixed_instances_policy_conflicting_overrides(autoscaling_group) {
    %autoscaling_group {
        MixedInstancesPolicy is_struct
        MixedInstancesPolicy {
            LaunchTemplate not exists or
            filter_launch_templates_conflicting_overrides(this)
        }
    }
}

rule filter_launch_templates_conflicting_overrides(launch_template) {
    %launch_template {
        LaunchTemplate is_struct
        LaunchTemplate {
            Overrides not exists or
            filter_overrides_conflicting_overrides(this)
        }
    }
}

rule filter_overrides_conflicting_overrides(overrides) {
    %overrides {
        Overrides is_list
        Overrides empty or
        some Overrides[*] {
            InstanceRequirements exists
            InstanceType exists
        }
    }
}

rule check_mutually_exclusive_property_combination(property1, property2) {
    %property1 not exists
    %property2 exists
}

#
# 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/
    }
}