implement everything needed for debouncing websocket message

This can be used with `WebsocketDemoWeb.Endpoint.broadcast!("demo:32211", "debounce_ping", %{})`

It requires that demo:id (which is dynamic based on id) is grabbed from the frontend manually

lib/websocket_demo_web/channels/demo_channel.ex

@@ -2,7 +2,7 @@ defmodule WebsocketDemoWeb.DemoChannel do
   require Logger
   use Phoenix.Channel
 
-  intercept []
+  intercept ["debounce_ping"]
 
   def join("demo:" <> _id, _params, socket) do
     timer_ref = Process.send(self(), :tick, [])
@@ -11,6 +11,7 @@ defmodule WebsocketDemoWeb.DemoChannel do
       socket
       |> assign(:current_tick, 0)
       |> assign(:tick_timer, timer_ref)
+      |> assign(:debounce_ping_debounce_state, :idle)
 
     {:ok, socket}
   end
@@ -45,4 +46,38 @@ defmodule WebsocketDemoWeb.DemoChannel do
 
     {:noreply, new_socket}
   end
+
+  def handle_info(:debounce_ping, socket = %{assigns: %{debounce_ping_debounce_state: :debouncing}}) do
+    new_socket =
+      socket
+      |> assign(:debounce_ping_debounce_state, :idle)
+      |> assign(:debounce_ping_debounce_timer, nil)
+
+    {:noreply, new_socket}
+  end
+
+  def handle_info(:debounce_ping, socket = %{assigns: %{debounce_ping_debounce_state: :called}}) do
+    {:noreply, handle_debounce_ping_call(socket)}
+  end
+
+  def handle_out("debounce_ping", _, socket = %{assigns: %{debounce_ping_debounce_state: :idle}}) do
+    {:noreply, handle_debounce_ping_call(socket)}
+  end
+
+  def handle_out("debounce_ping", _, socket = %{assigns: %{debounce_ping_debounce_state: :debouncing}}) do
+    {:noreply, assign(socket, :debounce_ping_debounce_state, :called)}
+  end
+
+  def handle_out("debounce_ping", _, socket = %{assigns: %{debounce_ping_debounce_state: :called}}) do
+    {:noreply, socket}
+  end
+
+  defp handle_debounce_ping_call(socket) do
+    push socket, "debounce_ping", %{}
+    timer = Process.send_after(self(), :debounce_ping, 3000)
+
+    socket
+      |> assign(:debounce_ping_debounce_state, :debouncing)
+      |> assign(:debounce_ping_debounce_timer, timer)
+  end
 end

test/websocket_demo_web/channels/demo_channel_test.exs

@@ -31,7 +31,7 @@ defmodule WebsocketDemoWeb.DemoChannelTest do
       assert :sys.get_state(socket.channel_pid).assigns.current_tick == 1
       Process.send(socket.channel_pid, :tick, [])
       assert :sys.get_state(socket.channel_pid).assigns.current_tick == 2
-      assert Process.read_timer(socket.assigns.tick_timer) == 5000
+      assert_in_delta Process.read_timer(socket.assigns.tick_timer), 5000, 10
     end
   end
 
@@ -65,4 +65,94 @@ defmodule WebsocketDemoWeb.DemoChannelTest do
       leave(socket)
     end
   end
+
+  describe "handle_out debounce_ping" do
+    test "state=idle, the socket receives an immediate push" do
+      {:ok, _, socket} =
+        socket(nil, %{})
+        |> subscribe_and_join(DemoChannel, "demo:1")
+
+      broadcast_from! socket, "debounce_ping", %{}
+      assert_push "debounce_ping", %{}
+    end
+
+    test "state=idle, the timer is setup for 3s from now, and sets the next state" do
+      {:ok, _, socket} =
+        socket(nil, %{})
+        |> subscribe_and_join(DemoChannel, "demo:1")
+
+      broadcast_from! socket, "debounce_ping", %{}
+      assert_push "debounce_ping", %{}
+
+      state = :sys.get_state(socket.channel_pid).assigns
+      assert_in_delta Process.read_timer(state.debounce_ping_debounce_timer), 3000, 10
+      assert state.debounce_ping_debounce_state == :debouncing
+    end
+
+    test "state=debouncing, the state is set to called" do
+      {:ok, _, socket} =
+        socket(nil, %{})
+        |> subscribe_and_join(DemoChannel, "demo:1")
+
+      broadcast_from! socket, "debounce_ping", %{}
+      assert_push "debounce_ping", %{}
+      broadcast_from! socket, "debounce_ping", %{}
+
+      state = :sys.get_state(socket.channel_pid).assigns
+      assert_in_delta Process.read_timer(state.debounce_ping_debounce_timer), 3000, 10
+      assert state.debounce_ping_debounce_state == :called
+    end
+
+    test "state=called, the state is not changed" do
+      {:ok, _, socket} =
+        socket(nil, %{})
+        |> subscribe_and_join(DemoChannel, "demo:1")
+
+      broadcast_from! socket, "debounce_ping", %{}
+      assert_push "debounce_ping", %{}
+      broadcast_from! socket, "debounce_ping", %{}
+      broadcast_from! socket, "debounce_ping", %{}
+
+      state = :sys.get_state(socket.channel_pid).assigns
+      assert_in_delta Process.read_timer(state.debounce_ping_debounce_timer), 3000, 10
+      assert state.debounce_ping_debounce_state == :called
+    end
+  end
+
+  describe "handle_info :debounce_ping" do
+    test "from state=debouncing, sets the state to idle without a push" do
+      {:ok, _, socket} =
+        socket(nil, %{})
+        |> subscribe_and_join(DemoChannel, "demo:1")
+
+      broadcast_from! socket, "debounce_ping", %{}
+      assert_push "debounce_ping", %{}
+
+      send socket.channel_pid, :debounce_ping
+
+      state = :sys.get_state(socket.channel_pid).assigns
+      assert state.debounce_ping_debounce_timer == nil
+      assert state.debounce_ping_debounce_state == :idle
+    end
+
+    test "from state=called, sets the state to debouncing with a push" do
+      {:ok, _, socket} =
+        socket(nil, %{})
+        |> subscribe_and_join(DemoChannel, "demo:1")
+
+      broadcast_from! socket, "debounce_ping", %{}
+      assert_push "debounce_ping", %{}
+      broadcast_from! socket, "debounce_ping", %{}
+
+      state = :sys.get_state(socket.channel_pid).assigns
+      assert state.debounce_ping_debounce_state == :called
+
+      send socket.channel_pid, :debounce_ping
+      assert_push "debounce_ping", %{}
+
+      state = :sys.get_state(socket.channel_pid).assigns
+      assert_in_delta Process.read_timer(state.debounce_ping_debounce_timer), 3000, 10
+      assert state.debounce_ping_debounce_state == :debouncing
+    end
+  end
 end