Generate a terraform module for an Elastic CI Stack for AWS CloudFormation Template

convert.rb

#!/usr/bin/env ruby

file = ARGV[0]
if file.nil?
  raise "Provide a path to a CloudFormation template"
end
$stderr.puts "Converting #{file}"

contents = File.read(file)

require 'yaml'
require 'json'
yaml = YAML.load(contents)

variables = []

parameters = yaml["Parameters"]
parameters.each_pair do |name, parameter|
  properties = {}

  if description = parameter["Description"]
    properties["description"] = description
  end

  type = parameter["Type"]
  if !type.nil?
    properties["type"] = case type
    when "String"
      "string"
    when "Number"
      "number"
    when "CommaDelimitedList"
      "list(string)"
    else
      raise "Unsupported type `#{type}`"
    end
  end

  if default = parameter["Default"]
    properties["default"] = case type
    when "CommaDelimitedList"
      default.split(",")
    else
      default
    end
  end

  condition_strings = []
  error_strings = []

  if allowedValues = parameter["AllowedValues"]
    condition_strings << "contains(#{allowedValues.to_json}, var.#{name})"
    error_strings << "#{name} must be one of #{allowedValues.join(', ')}."
  end

  if allowedPattern = parameter["AllowedPattern"]
    condition_strings << "can(regex(#{allowedPattern.to_json}, var.#{name}))"
    error_strings << "#{name} must match the regex \"#{allowedPattern}\"."
  end

  if minLength = parameter["MinLength"]
    condition_strings << "length(var.#{name}) >= #{minLength}"
    error_strings << "#{name} must have a length of at least #{minLength}."
  end

  if minValue = parameter["MinValue"]
    condition_strings << "var.#{name} >= #{minValue}"
    error_strings << "#{name} must have a value of at least #{minValue}."
  end

  if maxValue = parameter["MaxValue"]
    condition_strings << "var.#{name} <= #{maxValue}"
    error_strings << "#{name} must have a value of no more than #{maxValue}."
  end

  if constraintDescription = parameter["ConstraintDescription"]
    error_strings << "#{name} #{constraintDescription}"
  end

  if condition_strings.size > 0
    error_message = error_strings.join(' ')
    if error_message[-1] != "."
      error_message << "."
    end

    properties["validation"] = [
      {
        "condition" => "${#{condition_strings.join(' && ')}}",
        "error_message" => error_message,
      }
    ]
  end

  if noEcho = parameter["NoEcho"]
    properties["sensitive"] = true
  end

  variable = {
    name => [ properties ],
  }
  variables << variable
end

variables << {
  "StackName" => [
    {
      "type" => "string",
      "description" => "CloudFormation Stack Name",
      "default" => "buildkite"
    }
  ]
}

variables_by_parameters = {}
parameters.each_pair do |name, parameter|
  variables_by_parameters[name] = case parameter["Type"]
  when "CommaDelimitedList"
    "${join(\",\", var.#{name})}"
  else
    "${var.#{name}}"
  end
end

hcl = {
  "variable" => variables,
  "resource" => [
    {
      "aws_cloudformation_stack" => [
        {
          "elastic-ci-stack-for-aws": [
            {
              "capabilities": [
                "CAPABILITY_NAMED_IAM",
                "CAPABILITY_AUTO_EXPAND"
              ],
              "name": "${var.StackName}",
              # TODO make dynamic based on which template we are translating
              "template_url": "https://s3.amazonaws.com/buildkite-aws-stack/latest/aws-stack.yml",
              "parameters": variables_by_parameters
            }
          ]
        }
      ]
    }
  ]
}

puts JSON.pretty_generate(hcl)