module Locomotive::Steam
  module Middlewares

    # If an old URL has been found among the site url_redirections hash,
    # perform a 310 redirection to the new URL.
    # It is highly useful when the site existed before but was ran by another system.
    #
    # See the specs (spec/unit/middlewares/url_redirection_spec.rb) for more details.
    #
    class UrlRedirection < ThreadSafe

      include Helpers

      def _call
        if url = redirect_url
          emit_event

          redirect_to url
        end
      end

      protected

      def requested_url
        request.env['locomotive.path'] || request.fullpath
      end

      def emit_event
        ActiveSupport::Notifications.instrument('steam.serve.url_redirection', {
          site_id:  site._id,
          url:      requested_url
        })
      end

      def redirect_url
        return false if site.url_redirections.nil? || site.url_redirections.size == 0

        redirections_hash = site.url_redirections.to_h

        redirections_hash[requested_url] || find_dynamic_url_redirection(redirections_hash)
      end

      def find_dynamic_url_redirection(redirections_hash)
        number_of_segments = requested_url.split('/').size

        # attempt to find the first dynamic route which matches
        redirections_hash.each do |route, redirection|
          # a little bit of optimization
          next unless route.include?(':') && route.split('/').size == number_of_segments

          _regexp = route.gsub(/:([^\/]+)/, "(?<\\1>[^\/]+)").gsub('/', '\/')

          if matches = Regexp.new(_regexp).match(requested_url)
            matches.names.each { |n| redirection.gsub!(":#{n}", matches[n]) }

            return redirection
          end
        end

        false
      end

    end
  end

end