module Ajax
  module ActionController
    def self.included(klass)
      klass.class_eval do
        extend MirrorMethods
        include MirrorMethods
        after_filter :serialize_ajax_info
        include(Ajax.app.rails?(3) ? Rails3 : Rails2)
      end
    end

    module MirrorMethods

      # Set a custom response header if the request is AJAX.
      #
      # Call with <tt>key</tt> and optional <tt>value</tt>.  Pass a
      # block to yield a dynamic value.
      #
      # Accepts :only and :except conditions because we create
      # an after_filter.
      def ajax_header(*args, &block)
        return unless Ajax.is_enabled?

        options = args.extract_options!
        key, value = args.shift, args.shift
        value = block_given? ? Proc.new : value

        (self.is_a?(Class) ? self : self.class).prepend_after_filter(options) do |controller|
          if controller.request.xhr?
            value = value.is_a?(Proc) ? controller.instance_eval(&value) : value
            Ajax.set_header(controller.response, key, value)
          end
        end
      end

      # Set the layout to use for AJAX requests.
      #
      # By default we look in layouts/ajax/ for this controllers default
      # layout and render that.  If it can't be found, the default layout
      # is used.
      def ajax_layout(template_name)
        write_inheritable_attribute(:ajax_layout, template_name)
      end
    end

    module Rails2
      def self.included(klass)
        klass.class_eval do
          alias_method_chain :redirect_to_full_url, :ajax
          alias_method_chain :render, :ajax
        end
      end

      # Redirect to hashed URLs unless the path is excepted.
      #
      # Store the URL that we are redirecting to in the session.
      # If we then have a request for the root URL we know
      # to render this URL instead.
      #
      # If redirecting back to the referer, use the referer
      # in the Ajax-Info header because it includes the
      # hashed part of the URL.  Otherwise the referer is
      # always the root url.
      #
      # For AJAX requests, respond with an AJAX-suitable
      # redirect.
      #
      # This method only applies to Rails < 3
      def redirect_to_full_url_with_ajax(url, status)
        if !_ajax_redirect(url, status)
          redirect_to_full_url_without_ajax(url, status)
        end
      end

      #
      # Intercept rendering to customize the headers and layout handling
      #
      def render_with_ajax(options = nil, extra_options = {}, &block)
        return render_without_ajax(options, extra_options, &block) unless Ajax.is_enabled?

        original_args = [options, extra_options]
        if request.xhr?

          # Options processing taken from ActionController::Base#render
          if options.nil?
            options = { :template => default_template, :layout => true }
          elsif options == :update
            options = extra_options.merge({ :update => true })
          elsif options.is_a?(String) || options.is_a?(Symbol)
            case options.to_s.index('/')
            when 0
              extra_options[:file] = options
            when nil
              extra_options[:action] = options
            else
              extra_options[:template] = options
            end
            options = extra_options
          elsif !options.is_a?(Hash)
            extra_options[:partial] = options
            options = extra_options
          end

          default = pick_layout(options)
          default = default.path_without_format_and_extension unless default.nil?
          ajax_layout = _layout_for_ajax(default)
          ajax_layout = ajax_layout.path_without_format_and_extension unless ajax_layout.nil?
          options[:layout] = ajax_layout unless ajax_layout.nil?
        end
        render_without_ajax(options, extra_options, &block)
      end
    end

    module Rails3
      # Rails 3 hook.  Rails < 3 is handled using redirect_to_full_url.  See
      # those docs for info.
      def redirect_to(url={}, status={})
        if !_ajax_redirect(url, status)
          super
        end
      end

      # Specialize the default layout finder.  Try to use a layout in layouts/ajax
      # as the default layout, if one exists.
      def _default_layout(require_layout = false)
        if require_layout || !request.xhr? || !Ajax.is_enabled?
          super
        else
          layout_name = super
          if ajax_layout = _layout_for_ajax(layout_name)
            ajax_layout.virtual_path
          else
            layout_name
          end
        end
      end
    end

    protected

    # Convert the Ajax-Info hash to JSON before the request is sent.
    # Invoked as an after filter.
    #
    # Adds the current +layout+ and +controller+ to the hash.
    # These values will be sent in future requests using the Ajax-Info header.
    #
    # +controller+ is the result of calling ActionController#controller_name, so
    # if your controller is ApplicationController the value will be <tt>'application'</tt>.
    def serialize_ajax_info
      Ajax.set_header(response, :layout, Ajax.app.rails?(3) ? _layout : active_layout)
      Ajax.set_header(response, :controller, self.class.controller_name)
      response.headers['Ajax-Info'] = Ajax.send(:serialize_hash, response.headers['Ajax-Info'])
    end

    # Perform special processing on the response if we need to.
    # Return true if an Ajax "redirect" was performed, and false
    # otherwise.
    def _ajax_redirect(url, status)
      return false if url.nil? || !Ajax.is_enabled?
      special_redirect = false
      original_url = url

      # If we have the full referrer in Ajax-Info, use that because it
      # includes the fragment.
      if url == request.headers["Referer"] && !request.headers['Ajax-Info'].blank? && !request.headers['Ajax-Info']['referer'].blank?
        url = request.headers['Ajax-Info']['referer']
        Ajax.logger.debug("[ajax] using referer #{url} from Ajax-Info")
      end

      if !Ajax.exclude_path?(url)
        # Never redirect to the Ajax framework path, redirect to /
        if url =~ %r[#{Ajax.framework_path}]
          url = url.sub(%r[#{Ajax.framework_path}], '/')

          # Special case:
          #
          # Changing protocol forces a redirect from root to root.
          # The full request URL (including the hashed part) is
          # in the browser.  So return JS to do the redirect and
          # have it include the hashed part in the redirect URL.
          if !request.xhr? && URI.parse(url).scheme != URI.parse(request.url).scheme
            special_redirect = true
          end
        end

        if !Ajax.is_hashed_url?(url) and !Ajax.is_robot?(request.user_agent)
          url = Ajax.hashed_url_from_traditional(url)
        end
      end
      Ajax.logger.info("[ajax] rewrote redirect from #{original_url} to #{url}") unless original_url == url

      # Don't store session[:redirected_to] if doing a special redirect otherwise
      # when the next request for root comes in it will think we really want
      # to display the home page.
      if special_redirect
        session[:redirected_to] = nil
        Ajax.logger.info("[ajax] returning special redirect JS")
        render :layout => false, :text => <<-END
<script type="text/javascript">
var url = #{url.to_json};
var hash = document.location.hash;

// Remove leading # from the fragment
if (hash.charAt(0) == '#') {
  hash = hash.substr(1);
}

// Remove leading / from the fragment if the URL already ends in a /
// This prevents double-slashes.  Note we can't just replace all
// double-slashes because the protocol includes //.
if (url.charAt(url.length - 1) == '/' && hash.charAt(0) == '/') {
  hash = hash.substr(1);
}

document.location.href = url + hash;
</script>
END
      else
        session[:redirected_to] = url
        if request.xhr? && Ajax.is_hashed_url?(url)
          Ajax.logger.info("[ajax] detecting we are xhr. soft redirect")
          redirect_path = URI.parse(url).select(:fragment).first
          Ajax.logger.info("[ajax] redirect path is #{redirect_path}")
          Ajax.set_header(response, :soft_redirect, redirect_path)
          render :layout => false, :text => <<-END
<script type="text/javascript">
window.location.href = #{url.to_json};
</script>
END
        else
          Ajax.logger.info("[ajax] not detecting we are xhr. Hard redirect!")
          return false
        end
      end
      true
    end

    # Return the layout to use for an AJAX request, or nil if the default should be used.
    #
    # If no ajax_layout is set, look for the default layout in <tt>layouts/ajax</tt>.
    # If the layout cannot be found, use the default.
    def _layout_for_ajax(default) #:nodoc:
      ajax_layout = self.class.read_inheritable_attribute(:ajax_layout)
      ajax_layout = if ajax_layout.nil? && default.nil?
          nil
        elsif ajax_layout.nil? && !default.nil? # look for one with the default name in layouts/ajax
          "layouts/ajax/#{default.sub(/layouts(\/)?/, '')}"
        elsif ajax_layout && !(ajax_layout =~ /^layouts\/ajax/) # look for it in layouts/ajax
          "layouts/ajax/#{ajax_layout}"
        else # look as is
          ajax_layout
        end
      Ajax.app.rails?(3) ? find_template(ajax_layout) : find_layout(ajax_layout, 'html') if !ajax_layout.nil?
    rescue ::ActionView::MissingTemplate
      Ajax.logger.info("[ajax] no layout found in layouts/ajax.  Using #{default}.")
      nil
    end
  end
end