single-file-elixir/main.ex

counter = :counters.new(1, [])

Application.put_env(:sfe, Sfe.Endpoint,
  http: [ip: {127, 0, 0, 1}, port: 5001],
  adapter: Bandit.PhoenixAdapter,
  server: true,
  live_view: [signing_salt: "aaaaaaaa"],
  secret_key_base: String.duplicate("a", 64)
)

Application.put_env(:sfe, Sfe.HomeLive, counter_ref: counter)

Mix.install([
  {:bandit, "~> 1.2"},
  {:jason, "~> 1.0"},
  {:phoenix, "~> 1.7.0"},
  {:phoenix_live_view, "~> 0.19.0"},
  {:phoenix_pubsub, "~> 2.1"}
])


defmodule Sfe.ErrorView do
  def render(template, _), do: Phoenix.Controller.status_message_from_template(template)
end

defmodule Sfe.HomeLive do
  use Phoenix.LiveView, layout: {__MODULE__, :live}

  defp counter_ref(), do: Application.get_env(:sfe, __MODULE__)[:counter_ref]
  defp counter_value(), do: :counters.get(counter_ref(), 1)

  def mount(_params, _session, socket) do
    {:ok, assign(socket, :count, counter_value())}
  end

  defp phx_vsn, do: Application.spec(:phoenix, :vsn)
  defp lv_vsn, do: Application.spec(:phoenix_live_view, :vsn)

  def render("live.html", assigns) do
    ~H"""
    <script src={"https://cdn.jsdelivr.net/npm/phoenix@#{phx_vsn()}/priv/static/phoenix.min.js"}></script>
    <script src={"https://cdn.jsdelivr.net/npm/phoenix_live_view@#{lv_vsn()}/priv/static/phoenix_live_view.min.js"}></script>
    <script>
      let liveSocket = new window.LiveView.LiveSocket("/live", window.Phoenix.Socket)
      liveSocket.connect()
    </script>
    <style>
      * { font-size: 1.1em; }
    </style>
    <%= @inner_content %>
    """
  end

  def render(assigns) do
    ~H"""
    Multiplayer Counter
    <%= @count %>
    <button phx-click="inc">+</button>
    <button phx-click="dec">-</button>
    """
  end

  def handle_event("inc", _params, socket) do
    dbg(:counters.add(counter_ref(), 1, 1))
    counter_value(socket)
  end

  def handle_event("dec", _params, socket) do
    dbg(:counters.sub(counter_ref(), 1, 1))
    counter_value(socket)
  end

  defp counter_value(socket) do
    {:noreply, assign(socket, :count, counter_value())}
  end
end

defmodule Sfe.Router do
  use Phoenix.Router
  import Phoenix.LiveView.Router

  pipeline :browser do
    plug(:accepts, ["html"])
  end

  scope "/", Sfe do
    pipe_through(:browser)

    live("/", HomeLive, :index)
  end
end

defmodule Sfe.Endpoint do
  use Phoenix.Endpoint, otp_app: :sfe
  socket("/live", Phoenix.LiveView.Socket)
  plug(Sfe.Router)
end

children = [
  Sfe.Endpoint,
  {Phoenix.PubSub, name: :my_pubsub}
]

{:ok, _} = Supervisor.start_link(children, strategy: :one_for_one)

Process.sleep(:infinity)