# When the keyboard-layout indicator earns a place in the bar, and how a
# whole-swap bar is held to the same answer (BACKLOG #109).
#
# Pure so checks.waybar-language can unit-test the contract without building
# a bar. Consumed by modules/home/waybar.nix.
{ lib }:

rec {
  # The session's layouts are the comma-separated kb_layout.
  # nomarchy.keyboard.layouts is deliberately NOT among them — hyprland.nix
  # keeps it as the pool the new-keyboard picker offers first and never
  # merges it into kb_layout — so listing candidates cannot by itself make
  # the current layout ambiguous.
  sessionLayouts = layout: lib.filter (l: l != "") (lib.splitString "," layout);

  # The indicator answers "which layout am I typing in?", so it is worth bar
  # space exactly when that has more than one answer.
  #
  # devices    = declared nomarchy.keyboard.devices (submodules with .layout)
  # remembered = settings.keyboard.devices from the in-flake state: what the
  #              new-keyboard watcher writes the moment a layout is chosen.
  #              These only graduate into `devices` at the next rebuild, so a
  #              bar reading `devices` alone stays wrong for exactly as long
  #              as the memory is fresh — which is when it matters most.
  #
  # Counting devices rather than layouts is the trap: remembering "us" for a
  # device on a "us" session adds no second answer, and the rows a keyboard's
  # extra HID collections leave behind are all of that kind.
  show = { layout, devices ? { }, remembered ? { } }:
    let
      session = sessionLayouts layout;
      perDevice = lib.mapAttrsToList (_: d: d.layout) devices
        ++ lib.attrValues remembered;
    in
    lib.length session > 1 || lib.any (l: ! lib.elem l session) perDevice;

  # A whole-swap authors its bar in full and every one of them lists the
  # language module unconditionally, so without this a single-layout setup
  # showed on a swapped bar what the generated bar hides. Filter the swap
  # through the one answer rather than asking four hand-written files to
  # re-derive it (CONVENTIONS: the parity rule).
  gate = showLanguage: bar:
    if showLanguage then bar
    else
      lib.mapAttrs
        (n: v:
          if lib.hasPrefix "modules-" n && builtins.isList v
          then lib.filter (m: m != "hyprland/language") v
          else v)
        bar;
}