module Feedjira
  class Feed
    def self.parse_with(parser, xml, &block)
      parser.parse xml, &block
    end

    def self.parse(xml, &block)
      parser = determine_feed_parser_for_xml(xml)
      raise NoParserAvailable, 'No valid parser for XML.' unless parser
      parse_with parser, xml, &block
    end

    def self.determine_feed_parser_for_xml(xml)
      start_of_doc = xml.slice(0, 2000)
      feed_classes.detect { |klass| klass.able_to_parse?(start_of_doc) }
    end

    def self.add_feed_class(klass)
      feed_classes.unshift klass
    end

    def self.feed_classes
      @feed_classes ||= [
        Feedjira::Parser::RSSFeedBurner,
        Feedjira::Parser::GoogleDocsAtom,
        Feedjira::Parser::AtomYoutube,
        Feedjira::Parser::AtomFeedBurner,
        Feedjira::Parser::Atom,
        Feedjira::Parser::ITunesRSS,
        Feedjira::Parser::RSS
      ]
    end

    def self.add_common_feed_element(element_tag, options = {})
      feed_classes.each do |k|
        k.element element_tag, options
      end
    end

    def self.add_common_feed_elements(element_tag, options = {})
      feed_classes.each do |k|
        k.elements element_tag, options
      end
    end

    def self.add_common_feed_entry_element(element_tag, options = {})
      call_on_each_feed_entry :element, element_tag, options
    end

    def self.add_common_feed_entry_elements(element_tag, options = {})
      call_on_each_feed_entry :elements, element_tag, options
    end

    def self.call_on_each_feed_entry(method, *parameters)
      feed_classes.each do |klass|
        klass.sax_config.collection_elements.each_value do |value|
          collection_configs = value.select do |v|
            v.accessor == 'entries' && v.data_class.class == Class
          end

          collection_configs.each do |config|
            config.data_class.send(method, *parameters)
          end
        end
      end
    end

    def self.fetch_and_parse(url)
      response = connection(url).get
      unless response.success?
        raise FetchFailure, "Fetch failed - #{response.status}"
      end
      feed = parse response.body
      feed.feed_url = url
      feed.etag = response.headers['etag'].to_s.delete '"'

      feed.last_modified = parse_last_modified(response)
      feed
    end

    def self.connection(url)
      Faraday.new(url: url) do |conn|
        conn.use FaradayMiddleware::FollowRedirects, limit: 3
        conn.adapter :net_http
      end
    end

    def self.parse_last_modified(response)
      DateTime.parse(response.headers['last-modified']).to_time
    rescue
      nil
    end
    private_class_method :parse_last_modified
  end
end