refactor(web): share member-dropdown keyboard navigation between LiveViews

lib/mv_web/live/member_dropdown_nav.ex

@@ -0,0 +1,83 @@
+defmodule MvWeb.Live.MemberDropdownNav do
+  @moduledoc """
+  Shared keyboard-navigation logic for the member-search dropdown used by the
+  user form and the group show LiveViews.
+
+  Both views keep their own `member_dropdown_keydown` event entry point and their
+  own `select_focused_member/1` (the selection effect differs per view), but the
+  arrow/enter/escape navigation over `:focused_member_index` and the
+  dropdown-open guard are identical and live here.
+
+  The caller passes a zero-arity `select_focused` callback that performs the
+  view-specific selection of the currently focused entry.
+  """
+
+  import Phoenix.Component, only: [assign: 2]
+
+  @type socket :: Phoenix.LiveView.Socket.t()
+  @type result :: {:noreply, socket}
+
+  @doc """
+  Handles a `member_dropdown_keydown` event for the shared dropdown.
+
+  Navigation keys move `:focused_member_index` within
+  `[0, length(available_members) - 1]`; Enter invokes the view-specific
+  `select_focused` callback; Escape closes the dropdown; any other key is a
+  no-op. All key handling is guarded so that keystrokes while the dropdown is
+  closed are ignored.
+  """
+  @spec handle_keydown(map(), socket, (-> result)) :: result
+  def handle_keydown(%{"key" => "ArrowDown"}, socket, _select_focused) do
+    return_if_dropdown_closed(socket, fn ->
+      max_index = length(socket.assigns.available_members) - 1
+      current = socket.assigns.focused_member_index
+
+      new_index =
+        case current do
+          nil -> 0
+          index when index < max_index -> index + 1
+          _ -> current
+        end
+
+      {:noreply, assign(socket, focused_member_index: new_index)}
+    end)
+  end
+
+  def handle_keydown(%{"key" => "ArrowUp"}, socket, _select_focused) do
+    return_if_dropdown_closed(socket, fn ->
+      current = socket.assigns.focused_member_index
+
+      new_index =
+        case current do
+          nil -> 0
+          0 -> 0
+          index -> index - 1
+        end
+
+      {:noreply, assign(socket, focused_member_index: new_index)}
+    end)
+  end
+
+  def handle_keydown(%{"key" => "Enter"}, socket, select_focused) do
+    return_if_dropdown_closed(socket, select_focused)
+  end
+
+  def handle_keydown(%{"key" => "Escape"}, socket, _select_focused) do
+    return_if_dropdown_closed(socket, fn ->
+      {:noreply, assign(socket, show_member_dropdown: false, focused_member_index: nil)}
+    end)
+  end
+
+  def handle_keydown(_params, socket, _select_focused) do
+    # Ignore other keys
+    {:noreply, socket}
+  end
+
+  defp return_if_dropdown_closed(socket, func) do
+    if socket.assigns.show_member_dropdown do
+      func.()
+    else
+      {:noreply, socket}
+    end
+  end
+end