no guarantees that this doesn't require some other setting that I have in my config, but here's a start

gistfile1.txt

statusbar = {
  # formats:
  # when using {templates}, the template is shown only if its argument isnt
  # empty unless no argument is given. for example {sb} is printed always,
  # but {sb $T} is printed only if $T isnt empty.

  items = {
    # start/end text in statusbars
    barstart = "{sbstart}";
    barend = "{sbend}";

    # treated "normally", you could change the time/user name to whatever
    time = "";
    user = "{sb $cumode$N{sbmode $usermode}{sbaway $A}}";

    # treated specially .. window is printed with non-empty windows,
    # window_empty is printed with empty windows
    window = "{sb $winref:$T{sbmode $M}}";
    window_empty = "{sb $winref{sbservertag $tag}}";
    prompt = "{prompt $[.15]T}";
    prompt_empty = "{prompt $winname}";
    topic = " $topic";
    topic_empty = " Irssi v$J - http://irssi.org/help/";

    # all of these treated specially, theyre only displayed when needed
    lag = "{sb Lag: $0-}";
    act = "{sb Act: $0-}";
    more = "-- more --";
  };

  # theres two type of statusbars. root statusbars are either at the top
  # of the screen or at the bottom of the screen. window statusbars are at
  # the top/bottom of each split window in screen.
  default = {
    # the "default statusbar" to be displayed at the bottom of the window.
    # contains all the normal items.
    window = {
      disabled = "no";

      # window, root
      type = "window";
      # top, bottom
      placement = "bottom";
      # number
      position = "1";
      # active, inactive, always
      visible = "active";

      # list of items in statusbar in the display order
      items = {
        barstart = { priority = "100"; };
        time = { };
        user = { };
        window = { };
        window_empty = { };
        lag = { priority = "-1"; };
        act = { priority = "10"; };
        more = { priority = "-1"; alignment = "right"; };
        barend = { priority = "100"; alignment = "right"; };
      };
    };

    # statusbar to use in inactive split windows
    window_inact = {
      type = "window";
      placement = "bottom";
      position = "1";
      visible = "inactive";
      items = {
        barstart = { priority = "100"; };
        window = { };
        window_empty = { };
        more = { priority = "-1"; alignment = "right"; };
        barend = { priority = "100"; alignment = "right"; };
      };
    };

    # we treat input line as yet another statusbar :) Its possible to
    # add other items before or after the input line item.
    prompt = {
      type = "root";
      placement = "bottom";
      # we want to be at the bottom always
      position = "100";
      visible = "always";
      items = {
        prompt = { priority = "-1"; };
        prompt_empty = { priority = "-1"; };
        # treated specially, this is the real input line.
        input = { priority = "10"; };
      };
    };

    # topicbar
    topic = {
      type = "root";
      placement = "top";
      position = "1";
      visible = "always";
      items = {
        barstart = { priority = "100"; };
        topic = { };
        topic_empty = { };
        barend = { priority = "100"; alignment = "right"; };
      };
    };
  };
};