Invader: A simple preprocessor for terraform

invade

#!/usr/bin/env ruby
# A simple preprocessor for terraform.
#
# USAGE:
#
#   invade <template dir> <modules dir>
#
# This script will copy all tf files in the template dir to the modules dir
# and replace the `//invade <invader name> <args>` with the content of the
# invader file located at `./invader/<invader name>.tf`.
# The invader file is a piece of tf file with ERB template.
# The args are formed as `key=value` pairs.
#
require "fileutils"
require "erb"
from = ARGV.shift
to = ARGV.shift
if from.nil? || to.nil?
  puts "Usage: #{$0} <from> <to>"
  exit 1
end

INVADER_RE = %r{//invade\b(.+?)$}

# load invader files
$invaders = {}
Dir.glob("invader/**/*.tf").each do |path|
  name = File.basename(path, ".tf").sub(/^invader\//, "")
  $invaders[name] = File.read(path)
end

def invade(src)
  src.gsub(INVADER_RE) do |m|
    # get indent
    _, name, *args = m.split /\s+/
    hash = args.reduce({}) do |h, arg|
      k, v = arg.split("=")
      h[k] = v
      h
    end
    ERB.new($invaders[name]).result_with_hash hash
  end
end

Dir.glob("#{from}/**/*.tf").each do |path|
  path_to = path.sub(from, to)
  dirname = File.dirname(path_to)
  FileUtils.mkdir_p(dirname)
  src = File.read(path)
  dst = invade(src)
  File.open(path_to, "w") do |f|
    f.write(dst)
  end
end