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