Generate L10n file to rb and rbs

i18n_typed.rb

#! /usr/bin/env ruby

class Generator
  def initialize(base_locale:, root_name:, rb_path:, rbs_path:)
    @base_locale = base_locale.to_sym
    @root_name = root_name
    @rb_path = rb_path
    @rbs_path = rbs_path
    @stack = nil
    @mode = nil
    @indent = 0
  end

  def write
    I18n.with_locale(@base_locale) do
      write_rb { on_root }
      write_rbs { on_root }
    end
  end

  def write_rb
    @mode = :rb
    @io = File.open(@rb_path, 'w')
    yield
    $stdout.puts "Write rb to #{@rb_path}"
  end

  def write_rbs
    @mode = :rbs
    @io = File.open(@rbs_path, 'w')
    yield
    $stdout.puts "Write rbs to #{@rbs_path}"
  end

  def on_root
    puts "module #{@root_name}"
    nest do
      @stack = []
      on_member(I18n.config.backend.translations[@base_locale])
    end
    puts 'end'
  end

  def on_member(hash)
    hash.each_with_index do |(key, value), index|
      next unless key.match?(/^[a-z]/)

      @stack.push(key)

      case value
      when Hash
        puts "# #{@stack.join('.')}"
        case @mode
        when :rb
          puts "def self.#{under_score(key)} = #{camelcase(key)}"
        when :rbs
          puts "def self.#{under_score(key)}: () -> singleton(#{camelcase(key)})"
        end
        puts "module #{camelcase(key)}"
        nest do
          on_member(value)
        end
        puts 'end'
        puts if index != hash.size - 1
      when String, Array, Integer, true, false, nil
        case @mode
        when :rb
          puts "def self.#{under_score(key)} = ::I18n.t('#{@stack.join('.')}')"
        when :rbs
          case value
          when String
            # preview comment
            puts "# #{I18n.t(@stack.join('.')).split("\n", 2).first}"
            type = 'String'
          when Array
            type = 'Array[untyped]'
          when Integer
            type = 'Integer'
          else
            type = value.inspect
          end
          puts "def self.#{under_score(key)}: () -> #{type}"
        end
        puts if index != hash.size - 1
      when Proc
        # puts "def #{under_score(key)} = #{value.call.inspect}"
      else
        # binding.irb
      end

      @stack.pop
    end
  end

  def nest
    @indent += 1
    yield
    @indent -= 1
  end

  def puts(str = nil)
    if str
      @io.puts("#{'  ' * @indent}#{str}")
    else
      @io.puts
    end
  end

  def camelcase(sym)
    sym.to_s.camelcase.gsub(%r{[/-]}, '_')
  end

  def under_score(sym)
    sym.to_s.gsub(%r{[/-]}, '_')
  end
end

Generator.new(
  base_locale: :ja,
  root_name: 'L10n',
  rb_path: 'app/models/l10n.rb',
  rbs_path: 'sig/app/models/l10n.rbs',
).write