local RssChannel = {}
RssChannel.new = function(title, link, description, settings)
   local settings = settings or {}

   local channel = {
      title=title,
      link=link,
      description=description,
   }

   channel.language = settings.language
   channel.copyright = settings.copyright
   channel.managingEditor = settings.managingEditor
   channel.webMaster = settings.webMaster
   channel.lastBuildDate = settings.lastBuildDate
   channel.category = settings.category
   channel.generator = 'argent v0.1.0'
   channel.docs = 'https://www.rssboard.org/rss-specification'

   channel.items = {}

   setmetatable(
      channel,
      {
	 __index=RssChannel,
	 __tostring=RssChannel.tostring,
      }
   )
   return channel
end


RssChannel.addItem = function(self, tbl)
   local to_rfc822 = function(datestring, zone)
      if not string.match(datestring, '^%d%d%d%d%-%d%d%-%d%d$') then
	 error(string.format('%q is not a valid date string', datestring))
      end
      
      local year = string.match(datestring, '^%d%d%d%d')
      local month = string.match(datestring, '-(%d%d)-')
      local day = string.match(datestring, '%d%d$')

      local month_names = {'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'}
      month = month_names[tonumber(month)]

      return string.format('%s %s %s 00:00:00 %s', day, month, year, zone)
   end
   
   if not (tbl.title or tbl.description) then
      error('items must specify either a title or description!')
   end

   if not tbl.pubDate then
      error('items must specify a pubDate!')
   else
      tbl.pubDate = to_rfc822(tbl.pubDate, 'Z')
   end

   table.insert(self.items, tbl)
end


local tag_builder = function(source_table, indent_level)
   local str = ''
   local indent = string.rep('  ', indent_level)
   local add_tag = function(tag)
      if source_table[tag] then
	 str = str ..
	    string.format('%s<%s>%s</%s>\n',
			  indent, tag, source_table[tag], tag)
      end
   end
   local content = function()
      return str
   end
   return add_tag, content
end

local render_item = function(item_tbl)
   local add_tag, content = tag_builder(item_tbl, 2)
   add_tag('title')
   add_tag('link')
   add_tag('description')
   add_tag('author')
   add_tag('category')
   add_tag('comments')
   add_tag('guid')
   add_tag('pubDate')

   local indent = string.rep('  ', 1)
   return string.format('%s<item>\n%s%s</item>',
			indent, content(), indent)
end

RssChannel.tostring = function(self)
   local add_tag, content = tag_builder(self, 1)
   add_tag('title')
   add_tag('link')
   add_tag('description')

   add_tag('language')
   add_tag('copyright')
   add_tag('managingEditor')
   add_tag('webMaster')
   add_tag('pubDate')
   add_tag('lastBuildDate')
   add_tag('category')
   add_tag('generator')
   add_tag('docs')

   items_str = ''

   for _, item in ipairs(self.items) do
      items_str = items_str .. render_item(item) .. '\n'
   end

   return string.format(
      '<rss version="2.0">\n<channel>\n%s\n%s</channel>\n</rss>',
      content(), items_str)
end


RssChannel.save = function(self, filename)
   file = io.open(filename, 'w')
   file:write(self:tostring())
   file:close()
end


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]'
      if not set then return str end
      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 load_layouts(directory, parent, layouts)
      local directory = add_end_slash(directory) or ''
      local parent = parent or ''
      local layouts = layouts or {}

      local fullpath = parent..directory
      local dirs, files = argent.scanDirectory(argent.config.layout_directory..fullpath)

      for _, file in ipairs(files) do
	 if string.match(file, '%.lua$') then
	    local basename = string.gsub(file, '%.lua$', '')
	    local id = string.gsub(fullpath..basename, '/', '.')
	    argent.log('debug', fmt('loading layout %q', id))
	    success, result = pcall(loadfile(argent.config.layout_directory..fullpath..file), 0, 1)
	    if not success then
	       argent.log('error', result)
	       argent.log('warn', fmt('layout %q will not be available', id))
	    else
	       layouts[id] = result
	    end
	 end
      end

      for _, dir in ipairs(dirs) do
	 if dir ~= '.' and dir ~= '..' then
	    argent.log('debug', fmt('loading layouts from %q', parent..directory))
	    load_layouts(dir, parent..directory, layouts)
	 end
      end

      return layouts
   end


   function setup(config)
      argent.log('debug', 'begin setup')

      if not config.site_name then
	 error('site_name MUST be set!')
      end

      argent.config = {
	 site_name = config.site_name,
	 site_address = add_end_slash(config.site_address) or nil,
	 site_description = config.site_description or '',
	 site_language = config.site_language,
	 site_copyright = config.site_copyright,
	 
	 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.plugin_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 nil,
	 webmaster_email = config.webmaster_email,
      }

      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 =
	    add_end_slash(argent.currentWorkingDirectory())
	    ..argent.config.plugin_directory..'?.lua;'..package.path
      end

      if argent.config.layout_directory then
	 argent.layouts = load_layouts()
      else
	 argent.layouts = {}
      end
      argent.log('info', fmt('available layouts: %s', set_tostring(argent.layouts)))
      
      if argent.config.rss_include then
	 if not argent.config.site_address then
	    error('rss_include is set, but site_address is not!')
	 end
	 argent.rss_channel = RssChannel.new(
	    argent.config.site_name,
	    argent.config.site_address,
	    argent.config.site_description,
	    { language = argent.config.site_language,
	      copyright = argent.config.site_copyright,
	      webMaster = argent.config.webmaster_email,
	    }
	 )
      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', parent..file))
	 return true
      end

      argent.log('debug', fmt('removing file %q', parent..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', parent..dir))
	 return true
      end

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


   function obliterate(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 should_include(filename, parent)
      for pattern in pairs(argent.config.include) do
	 if string.match(filename, pattern) or string.match(parent..filename, pattern) then
	    return true
	 end
      end
      return false
   end

   function should_ignore(filename, parent)
      if is_dotfile(filename) and not should_include(filename, parent) then
	 return false
      end

      for pattern in pairs(argent.config.exclude) do
	 if string.match(filename, pattern)
	    or string.match(parent..filename, pattern) then
	    return true
	 end
      end

      return false
   end

   function should_process(filename, parent)
      if not string.match(filename, '%.lua$') then
	 return false
      end
      
      if should_ignore(filename, parent) then
	 return false
      end

      for pattern in pairs(argent.config.noprocess) do
	 if string.match(filename, pattern)
	    or string.match(parent..filename, pattern) then
	    return false
	 end
      end

      return true
   end

   function process_file(filename, parent)
      if should_ignore(filename, parent) then
	 argent.log('debug', fmt('will not process file %q', parent..filename))
	 return
      end

      if should_process(filename, parent) then
	 argent.log('debug', fmt('processing %q as lua file', parent..filename))
	 process_lua_file(filename, parent)
      else
	 argent.log('debug', fmt('processing %q as regular file', parent..filename))
	 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
	 argent.log('error', result)
	 argent.log('warn', fmt('%q will not be processed for output!', parent..filename))
	 return
      end

      if not type(result) == 'table' then
	 argent.log('error', fmt('%q returned %q instead of %q', filename, type(result), 'table'))
	 argent.log('warn', fmt('%q will not result in file output!', filename))
	 return
      end

      local html
      if result.html then
	 html = result.html
      elseif result.markdown then
	 html = argent.markdown(result.markdown)
      else
	 argent.log('error', fmt('%q did not specify any content!', filename))
	 argent.log('warn', fmt('%q will not result in file output!', filename))
	 return
      end

      if not result.title then
	 result.title = string.gsub(filename, '%.lua$', '')
	 argent.log('warn', fmt('%q did not specify a title; using default title of %q',
				filename, result.title))
      end

      local layout = function(html, tbl) return html end
      if result.layout then
	 if not argent.layouts[result.layout] then
	    argent.log('error', fmt('%q requested nonexistent layout %q', filename, result.layout))
	    argent.log('warn', fmt('%q will not result in file output!', filename))
	    return
	 else
	    layout = argent.layouts[result.layout]
	 end
      else -- no layout specified
	 argent.log('warn', fmt(
		       '%q did not specify a layout; output will be naked content!',
		       filename))
      end

      local output_data = layout(html, result)
      local output_name = string.gsub(filename, '%.lua$', '.html')
      local output_file = io.open(argent.config.output_directory..parent..output_name, 'w')
      output_file:write(output_data)
      output_file:close()

      if argent.rss_channel then
	 for pattern in pairs(argent.config.rss_include) do
	    if string.match(filename, pattern)
	       or string.match(parent..filename, pattern)
	    then -- add to the RSS feed!
	       if not result.date then
		  argent.log(
		     'warn',
		     fmt(
			'%q did not specify a date; it will not be included in rss.xml!',
			parent..filename
		     )
		  )
		  return
	       end
	       
	       argent.rss_channel:addItem{
		  title=result.title,
		  link=argent.config.site_address..parent..output_name,
		  description = result.description,
		  pubDate = result.date,
	       }
	    end
	 end
      end
   end


   function process_dir(directory, parent)
      if should_ignore(directory, parent) then
	 argent.log('debug', fmt('will not process directory %q', parent..directory))
	 return
      end

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


   function process(directory, parent)
      local directory = add_end_slash(directory) or ''
      local parent = 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()
   end
   process()

   if argent.rss_channel then
      argent.rss_channel:save(argent.config.output_directory..'rss.xml')
   end
end