Focus management for multi-panel apps.

Focus is a tiny state machine over an ordered ring of focusable IDs. You declare the IDs up front, feed every key event through handle_key/2, and pattern-match on current/1 to decide which widget receives the keystroke. handle_key/2 consumes Tab / Shift+Tab (or your overrides) and passes everything else through unchanged.

There is no process, no macro, no protocol — just a struct you keep in your reducer state or ExRatatui.App model.

Caller pattern

def handle_event(%Event.Key{} = key, state) do
  {focus, key} = Focus.handle_key(state.focus, key)
  state = %{state | focus: focus}

  case key do
    nil ->
      # consumed by Focus (Tab / Shift+Tab); nothing more to do
      state

    key ->
      case Focus.current(focus) do
        :search  -> update_search(state, key)
        :results -> update_results(state, key)
        :details -> update_details(state, key)
      end
  end
end

Styling the focused widget

Focus never touches widget structs. Use focused?/2 to decide the style yourself:

border_style =
  if Focus.focused?(focus, :search),
    do: %Style{fg: :yellow},
    else: %Style{fg: :gray}

%TextInput{
  state: search_state,
  block: %Block{borders: :all, border_style: border_style}
}

Custom keys

Pass :next_keys / :prev_keys to new/2 as lists of %ExRatatui.Event.Key{} structs. Only :code and :modifiers matter — :kind is ignored, and :modifiers is compared as a set (order-independent).

Focus.new([:a, :b, :c],
  next_keys: [%Event.Key{code: "tab"}, %Event.Key{code: "right", modifiers: ["ctrl"]}],
  prev_keys: [%Event.Key{code: "left", modifiers: ["ctrl"]}]
)