De-duplicating Terraform code by generating it from JavaScript

terraform-util.js

const fs = require('fs')

module.exports = {
  writeTerraform,
  generateMain,
}

// Templates are just terraform (.tf files) with the following kinds of interpolations:
// 1. Variables embedded in a string: "terraform-states-<id>"
// 2. Variables occupying an entire string: "<apiId>".
//    If the value is a string then double quotes are preserved and for most other data types they are not (for say a number).
//    If value is an object then quotes are preserved if quotes === true, example object value without quotes:
//    { value: `aws_api_gateway_deployment.${api}.stage_name`, quotes: false }
// 2. As a comment on its own line for a block of code: #<lambdas>
function template (name, variables) {
  const code = fs.readFileSync(`_terraform/templates/${name}.tf`).toString()
  return code.replace(/#?"?<([a-z0-9]+)>"?/gi, (m, key) => {
    const value = variables[key]
    if (m.startsWith('"') && m.endsWith('"')) {
      if (typeof value === 'string') {
        return `"${value}"`
      } else if (typeof value === 'object' && value.value) {
        return value.quotes ? `"${value.value}"` : value.value
      } else {
        return value
      }
    } else if (m.startsWith('"') && !m.endsWith('"')) {
      return `"${value}`
    } else if (!m.startsWith('"') && m.endsWith('"')) {
      return `${value}"`
    } else {
      return value
    }
  })
}

function writeTerraform (code, options = {})  {
  if (Array.isArray(code)) code = code.join('\n')
  const tfPath = (options.path || process.argv[1] || 'main.js').replace(/\.js$/, '.tf')
  fs.writeFileSync(tfPath, code)
}

// Example Terraform generation from a main.tf template
function generateMain () {
  const variables = {
    api,
    name,
    body: { value: `data.template_file.openapi_${api}.rendered`, quotes: false },
    restApiId: { value: `aws_api_gateway_rest_api.${api}.id`, quotes: false },
    apiId: { value: `aws_api_gateway_rest_api.${api}.id`, quotes: false },
    stageName: { value: `aws_api_gateway_deployment.${api}.stage_name`, quotes: false }
  }
  return template('main', variables)
}