Sort YAML files while keeping the comments intact

yaml-keysort.rb

#!/usr/bin/env ruby
#
# yaml-keysort.rb - Sort YAML files by key while keeping comments intact
#
# Note: script does not parse YAML and copies lines entirely, only keeping track of top-level keys.
# Ensure there is a blank line between each block.

# frozen_string_literal: true

file = ARGV.pop

abort("Usage: #{$0} FILE") unless file

file = File.expand_path(File.join(__dir__, file))
output = File.join(File.dirname(file), "#{File.basename(file, ".yml")}.sorted.yml")

abort("File not found: #{file}") unless File.exist?(file)

lines = File.readlines(file)

configuration = { key: "", comments: [], lines: [] }

configurations = lines.each_with_object([]) do |e, a|
  case e
  when /^\n$/
    # Finalize configuration block
    a << configuration
    configuration = { key: "", comments: [], lines: [] }
  when /^#/
    # Save comments preceding key definition
    configuration[:comments] << e
  when /^  /
    # Save lines following key definition
    configuration[:lines] << e
  else
    # Save key definition
    configuration[:lines] << e
    configuration[:key] = e.chomp.delete_suffix(":")
  end
end

lines = configurations
  .reject { |c| c.fetch(:key) == "" }
  .sort_by { |c| c.fetch(:key) }
  .map { |c| c.fetch(:comments).concat(c.fetch(:lines)).join }
  .join("\n")

File.write(output, lines)

puts "Written sorted keys to #{output}"