return function(config)
   local fmt = string.format

   --------------------------------
   --
   -- basics
   --
   --------------------------------

   function Set(array, transform)
      if type(array) ~= 'table' then return nil end

      local transform = transform or function(x) return x end

      local set = {}
      for _, element in ipairs(array) do
	 set[transform(element)] = true
      end
      return set
   end

   function set_tostring(set)
      local str = '[empty]'
      for element in pairs(set) do
	 if str == '[empty]' then
	    str = tostring(element)
	 else
	    str = str .. '; '.. tostring(element)
	 end
      end

      return str
   end


   function add_end_slash(str)
      if type(str) ~= 'string' then return nil end
      if string.match(str, '/$') then return str end
      return str .. '/'
   end


   function strip_end_slash(str)
      if string.match(str, '/$') then return string.sub(str, 1, #str-1) end
      return str
   end


   function setup(config)
      argent.log('debug', 'begin setup')
      
      argent.config = {
	 site_directory = add_end_slash(config.site_directory) or 'site/',
	 output_directory = add_end_slash(config.output_directory) or 'public/',
	 layout_directory = add_end_slash(config.layout_directory) or nil,
	 plugin_directory = add_end_slash(config.layout_directory) or nil,
	 exclude = Set(config.exclude, strip_end_slash) or {},
	 include = Set(config.include, strip_end_slash) or {},
	 keep = Set(config.keep, strip_end_slash) or {},
	 noprocess = Set(config.noprocess, strip_end_slash) or {},
	 rss_include = Set(config.rss_include, strip_end_slash) or {},
      }

      argent.log('info', fmt('site directory: %s', argent.config.site_directory))
      argent.log('info', fmt('output directory: %s', argent.config.output_directory))
      argent.log('info', fmt('layout directory: %s', tostring(argent.config.layout_directory)))
      argent.log('info', fmt('plugin directory: %s', tostring(argent.config.plugin_directory)))

      argent.log('info', 'exclusions: '..set_tostring(argent.config.exclude))
      argent.log('info', 'inclusions: '..set_tostring(argent.config.include))
      argent.log('info', 'files to keep: '..set_tostring(argent.config.keep))
      argent.log('info', 'noprocess: '..set_tostring(argent.config.noprocess))
      argent.log('info', 'rss files: '..set_tostring(argent.config.rss_include))

      if argent.config.plugin_directory then
	 package.path = argent.config.plugin_directory..'?.lua;'..package.path
      end
      argent.log('debug', 'end setup')
   end


   function is_dotfile(filename)
      if string.match(filename, '^%.') then return true end
      return false
   end


   function directory_exists(directory, parent)
      local directory = directory or ''
      local parent = parent or ''
      local dirs = argent.scanDirectory(argent.config.output_directory..parent)
      for _, dir in ipairs(dirs) do
	 if strip_end_slash(directory) == dir then return true end
      end
      return false
   end


   function output_directory_exists()
      local dirs = argent.scanDirectory('./')
      for _, dir in ipairs(dirs) do
	 if add_end_slash(dir) == argent.config.output_directory then
	    return true
	 end
      end
      return false
   end


   --------------------------------
   --
   -- obliterating
   --
   --------------------------------

   function obliterate_file(file, parent)
      if argent.config.keep[file] then
	 argent.log('debug', fmt('retaining file %q', file))
	 return true
      end

      argent.log('debug', fmt('removing file %q', file))
      os.remove(argent.config.output_directory..parent..file)
      return false
   end


   function obliterate_dir(dir, parent)
      if argent.config.keep[strip_end_slash(dir)] then
	 argent.log('debug', fmt('retaining directory %q', dir))
	 return true
      end

      argent.log('debug', fmt('obliterating files in %q', parent..dir))
      return obliterate_directory(dir, parent)
   end


   function obliterate_directory(dirname, parent)
      local dirname = add_end_slash(dirname) or ''
      local parent = parent or ''

      if argent.config.keep[dirname] then return true end

      local keep_self = (dirname == '')

      local dirs, files = argent.scanDirectory(argent.config.output_directory..parent..dirname)
      for _, file in ipairs(files) do
	 keep_self = obliterate_file(file, parent..dirname) or keep_self
      end
      for _, dir in ipairs(dirs) do
	 if dir ~= '.' and dir ~= '..' then
	    keep_self = obliterate_dir(dir, parent..dirname) or keep_self
	 end
      end

      if not keep_self then
	 os.remove(argent.config.output_directory..parent..dirname)
	 return false
      else
	 return true
      end
   end


   --------------------------------
   --
   -- processing
   --
   --------------------------------

   function process_file(filename, parent)
      if (is_dotfile(filename) and not argent.config.include[filename])
	 or argent.config.exclude[filename]
      then return end

      if string.match(filename, '%.lua$') and not argent.config.noprocess[filename] then
	 process_lua_file(filename, parent)
      else
	 argent.copyFile(
	    argent.config.site_directory..parent..filename,
	    argent.config.output_directory..parent..filename
	 )
      end
   end


   function process_lua_file(filename, parent)
      local success, result = pcall(loadfile(argent.config.site_directory..parent..filename))
      if not success then
	 print('WARNING: '..result)
	 return
      end

      print(filename, result)
   end


   function process_dir(directory, parent)
      if (is_dotfile(directory) and not argent.config.include[strip_end_slash(directory)])
	 or argent.config.exclude[strip_end_slash(directory)]
      then return end

      if not directory_exists(directory, parent) then
	 argent.createDirectory(argent.config.output_directory..parent..directory)
      end
      process_directory(directory, parent)
   end


   function process_directory(directory, parent)
      local directory = add_end_slash(directory) or ''
      local parent = add_end_slash(parent) or ''
      local dirs, files = argent.scanDirectory(argent.config.site_directory..parent..directory)
      for _, file in ipairs(files) do
	 process_file(file, parent..directory)
      end

      for _, dir in ipairs(dirs) do
	 if dir ~= '.' and dir ~= '..' then
	    process_dir(dir, parent..directory)
	 end
      end
   end


   --------------------------------
   --
   -- putting it all together
   --
   --------------------------------

   setup(config)
   if not output_directory_exists() then
      argent.createDirectory(argent.config.output_directory)
   else
      obliterate_directory()
   end
   process_directory()
end