gistfile1.rb

def next_page(format = 'markdown')
  chapter = params[:chapter] || :toc
  page_name = params[:page_name]
  current_file = Dir["#{Merb.root}/book-content/#{language}/*-#{chapter}/*-#{page_name||"*"}.#{format}"].entries.first
  if current_file
    current_file.grep(/book-content\/\w{2}\/(\d{1,})[-]\w+[-]\w+\/(\d{1,})[-]\w+[.]\w+/)
    chapter_number = $1
    page_number    = $2
  end
  next_file = Dir["#{Merb.root}/book-content/#{language}/#{chapter_number}-*/#{page_number.to_i + 1}-*.#{format}"].entries.first
  if next_file
    next_file.grep(/book-content\/\w{2}\/\d{1,}[-]\w+[-]?\w+\/\d{1,}[-](\w+[-]?\w+)[.]\w+/)
    page_name = $1
  end
  link_to('Next', url(:page, :language => language, :chapter => chapter, :page_name => page_name))
end