Jekyll Theme switcher by Oreolek

themes.rb

# you should add something like this to your config:
# theme: theme-name

module Jekyll
  module Theme
    class ThemeChooser < Generator
      safe false
      
      def generate(site)
        themes_path = '_themes/'
        target_path = site.config['source'] + '/_layouts'
        unless site.config['theme'] then
          unless (Dir.entries(target_path).size - 2 > 0) then
            STDERR.puts 'theme parameter is not set. The _layouts directory is not empty. Theme will not be generated.'
            return
          end
          puts "theme parameter is not set. Using _layouts directory. The plugin will now exit."
          return
        end
        
        theme = File.join(themes_path, site.config['theme'])
        unless FileTest.directory?(theme) then
          STDERR.puts "Theme directory #{theme} not found. Theme will not be generated."
          return
        end
        
        print "Copying theme '#{site.config['theme']}'.."
        FileUtils.cp_r(Dir.getwd + '/' + theme + '/.', target_path)
        puts "."
        site.read_layouts
        puts "done."
      end
    end
  end
end