{
  pkgs,
  config,
  lib,
  ...
}:
with lib;
let
  calwatcher =
    (pkgs.writeShellApplication {
      name = "calwatcher";
      runtimeInputs = [
        pkgs.inotify-tools
        pkgs.khal
        pkgs.jq
      ];
      text = ''
         # in parts ripped from https://git.sr.ht/~whynothugo/dotfiles/tree/3768ec57/item/home/.local/lib/waybar-khal
         render() {
          # Find events starting in two minutes.
          # So if my current event ends in two minutes and another one starts, the
          # widget is already updated with what's upcoming.
          SINCE="$(date -d 'now +2 min' '+%FT%H:%M:%S')"
          UNTIL="1d"

          EVENT="$(
            khal list "$SINCE" "$UNTIL" \
              --day-format 'SKIPME' \
              --format "{start-end-time-style} {title:.31}{repeat-symbol}" |
              grep -v SKIPME |  # filter out headers
              grep -v -P '↦|↔ |⇥' |  # filter out continuing all day events
              grep -v '^ ' |  # exclude full-day events
              head -n 1  # show just the first
          )"

          if [ -z "$EVENT" ]; then
            TEXT="  (nothing upcoming)"
            CLASS="no-event"
          else
            TEXT="  $EVENT"
            CLASS="event"
          fi

          jq --compact-output \
            --null-input \
            --arg text "$TEXT" \
            --arg class "$CLASS" \
            --arg tooltip "$(khal list today 7d --day-format '<span color="#ffead3"><b>{name} {date-long}</b></span>')" \
            '{"text": $text, "class": $class, "tooltip": $tooltip}'
        }

        render # Render once for initial state.

        # In order to make sure events are updated as time passes, this re-renderes
        # every two minutes. That aside, whenever a calendar event changes, we alreays
        # re-render immediately.
        #
        # It would be ideal to determine _when_ the current event ends, and set the
        # timeout accordinly. That would require parsing khal's output a bit more.
        while true; do
          # (inotifywait \
          #   --event modify \
          #   --event create \
          #   --event delete \
          #   --event close_write \
          #   --event moved_to \
          #   --event move \
          #   --monitor \
          #   --timeout 120 \
          #   --recursive \
          #   "$HOME/.calendars" 2> /dev/null) || true | \
          #   while read -r _; do
          # TODO: fix inotify stuff
              render
              sleep 30
              # timeout 3 cat || true # debounce for 3s, https://stackoverflow.com/a/69945839
            # done
        done
      '';

    })
    + "/bin/calwatcher";
in
lib.mkIf (config.xyno.user-services.khal.enable) {
  xyno.desktop.waybar.config = {
    "custom/cal" = {
      exec = calwatcher;
      restart-interval = 5;
      return-type = "json";
      "on-click" = "${pkgs.foot}/bin/footclient --app-id floating-alacritty ${pkgs.khal}/bin/ikhal";
    };
    modules-right = mkOrder 1999 [ "custom/cal" ]; # left of clock, right of everything else
  };

}