format_scala_case_class.rb

#!/usr/bin/env ruby

class Machine
  INDENT = '  '

  def initialize
    @indent_level = 0
  end

  def incr_indent(n = 1)
    @indent_level += n
  end

  def decr_indent(n = 1)
    @indent_level -= n
  end

  def format(char)
    case char
    when /[\(\{\[]/
      incr_indent
      char + next_line
    when /[\)\}\]]/
      decr_indent
      next_line + char
    when ','
      char + next_line
    else
      char
    end
  end

  private def next_line
    indent = @indent_level > 0 ? INDENT * @indent_level : ''
    "\n" + indent
  end
end

machine = Machine.new
puts ARGF.read.each_char.map {|c|
  machine.format(c)
}.join('')