IRC 風構文解析

like_irc_parser.rb

require 'strscan'

module Converter
  AVAILABLE_TAGS = {
    /<bold>/ => {
      start_tag: '<b>',
      end_tag: '</b>'
    },
    /<underline>/ => {
      start_tag: '<u>',
      end_tag: '</u>'
    }
  }
  STOP_TAG = /<stop>/

  def convert(source)
    scanner = StringScanner.new(source)
    opened_tags = []
    result = ''

    until scanner.eos?
      if scanner.scan(STOP_TAG)
        until opened_tags.empty?
          tag = opened_tags.pop
          result << tag[:end_tag]
        end

        next
      end

      AVAILABLE_TAGS.each do |pattern, tag|
        if scanner.scan(pattern)
          result << tag[:start_tag]
          opened_tags.push(tag)

          next
        end
      end

      result << scanner.getch
    end

    raise 'opened tags remain' until opened_tags.empty?

    result
  end
  module_function :convert
end

s_good = 'foo<bold>bar<underline>baz<stop>qux'
print("#{s_good} -> ")
puts(Converter.convert(s_good))

begin
  s_bad = 'foo<bold>bar<underline>baz'
  print("#{s_bad} -> ")
  puts(Converter.convert(s_bad))
rescue => e
  puts(e)
end