{
  config,
  lib,
  pkgs,
  ...
}:
# Waybar: a top status bar reading system state at a glance.
let
  waybarModulesFor =
    position:
    map (module: module.name) (
      lib.sort (a: b: a.order < b.order) (
        lib.filter (module: module.position == position) (staticWaybarModules ++ registeredWaybarModules)
      )
    );

  staticWaybarModules = [
    {
      name = "hyprland/workspaces";
      position = "left";
      order = 10;
    }
    {
      name = "clock";
      position = "center";
      order = 10;
    }
    {
      name = "mpris";
      position = "right";
      order = 30;
    }
    {
      name = "wireplumber";
      position = "right";
      order = 40;
    }
    {
      name = "custom/network";
      position = "right";
      order = 60;
    }
    {
      name = "battery";
      position = "right";
      order = 70;
    }
  ];

  registeredWaybarModules = lib.mapAttrsToList (
    name: module:
    module
    // {
      inherit name;
    }
  ) hostWaybarModules;

  hostWaybarModules = lib.attrByPath [ config.networking.hostName ] { } config.registry.waybar;

  # A Nerd Font Private-Use-Area codepoint as a literal character, decoded
  # through JSON so the glyph survives as bytes rather than an editor paste.
  g = code: builtins.fromJSON ''"\u${code}"'';

  registeredWaybarModuleSettings = lib.mapAttrs (_name: module: module.settings) hostWaybarModules;

  networkStatus = pkgs.writeShellScript "waybar-network-status" ''
    active=$(
      ${lib.getExe' pkgs.networkmanager "nmcli"} -t -f DEVICE,TYPE,STATE,CONNECTION device status \
        | ${lib.getExe' pkgs.gawk "awk"} -F: '$3 == "connected" && $2 != "loopback" { print; exit }'
    )

    if [ -z "$active" ]; then
      ${lib.getExe pkgs.jq} -cn \
        --arg text "${g "f127"} off" \
        --arg tooltip "Network disconnected" \
        --arg class "disconnected" \
        '{ text: $text, tooltip: $tooltip, class: $class }'
      exit 0
    fi

    IFS=: read -r device type _state connection <<< "$active"

    case "$type" in
      wifi) icon="${g "f1eb"}" ;;
      ethernet) icon="LAN" ;;
      *) icon="NET" ;;
    esac

    ipaddr=$(${lib.getExe' pkgs.iproute2 "ip"} -4 -o addr show dev "$device" | ${lib.getExe' pkgs.gawk "awk"} '{ print $4; exit }')

    ${lib.getExe pkgs.jq} -cn \
      --arg text "$icon $connection" \
      --arg tooltip "$device: ''${ipaddr:-no IPv4}" \
      --arg class "$type" \
      '{ text: $text, tooltip: $tooltip, class: $class }'
  '';
in
{
  options.modules.desktop.session.waybar.enable = lib.mkEnableOption "the Waybar status bar";

  config = lib.mkIf config.modules.desktop.session.waybar.enable {
    # A symbols font backs the module glyphs, so pango falls back to it for the
    # codepoints Stylix's monospace font does not carry.
    fonts.packages = [ pkgs.nerd-fonts.symbols-only ];

    home-manager.users.${config.user.name}.programs.waybar = {
      enable = true;

      # A user service bound to graphical-session.target, which uwsm activates,
      # so the bar comes up with the session and no compositor exec-once.
      systemd.enable = true;

      style = ''
        .modules-right {
          margin-right: 8px;
        }

        #custom-dnd {
          margin-right: 8px;
        }
      '';

      settings.mainBar = lib.mkMerge [
        {
          layer = "top";
          position = "top";
          height = 30;
          spacing = 8;

          modules-left = waybarModulesFor "left";
          modules-center = waybarModulesFor "center";
          modules-right = waybarModulesFor "right";

          # Per-application icons for the windows on each workspace, mapped from
          # window class with a neutral glyph for anything unlisted.
          "hyprland/workspaces" = {
            on-click = "activate";
            format = "{id} {windows}";
            format-window-separator = " ";
            window-rewrite-default = g "f2d0";
            window-rewrite = lib.mapAttrs' (
              _name: windowIcon: lib.nameValuePair "class<${windowIcon.class}>" (g windowIcon.icon)
            ) (lib.attrByPath [ config.networking.hostName ] { } config.registry.window-icon);
          };

          clock = {
            format = "{:%a %d %b  %H:%M}";
            tooltip-format = "<tt>{calendar}</tt>";
            calendar = {
              mode = "month";
              # Underline the current day so it stands out in the grid.
              format.today = "<b><u>{}</u></b>";
            };
          };

          mpris = {
            format = "${g "f001"} {title}";
            format-paused = "${g "f04c"} {title}";
            max-length = 40;
            on-click = "play-pause";
            on-scroll-up = "next";
            on-scroll-down = "previous";
          };

          wireplumber = {
            format = "{icon} {volume}%";
            format-muted = "${g "f026"} muted";
            format-icons = [
              (g "f026")
              (g "f027")
              (g "f028")
            ];
            on-click = "${lib.getExe' pkgs.wireplumber "wpctl"} set-mute @DEFAULT_AUDIO_SINK@ toggle";
          };

          "custom/network" = {
            return-type = "json";
            exec = "${networkStatus}";
            interval = 5;
          };

          battery = {
            format = "{icon} {capacity}%";
            format-charging = "${g "f0e7"} {capacity}%";
            format-icons = [
              (g "f244")
              (g "f243")
              (g "f242")
              (g "f241")
              (g "f240")
            ];
            states = {
              warning = 20;
              critical = 10;
            };
          };
        }
        registeredWaybarModuleSettings
      ];
    };
  };
}