dwyl · SimonLab · Jun 20, 2022 · Jun 17, 2022 · Jun 17, 2022 · Jun 17, 2022
diff --git a/.github/dependabot.yml b/.github/dependabot.yml
@@ -0,0 +1,8 @@
+version: 2
+updates:
+- package-ecosystem: mix
+  directory: "/"
+  schedule:
+    interval: daily
+    time: "07:00"
+    timezone: Europe/London
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -30,6 +30,8 @@ jobs:
         restore-keys: ${{ runner.os }}-mix-
     - name: Install dependencies
       run: mix deps.get
-    - name: Run tests
-      run: mix test
+    - name: Run Tests
+      run: mix coveralls.json
+    - name: Upload coverage to Codecov
+      uses: codecov/codecov-action@v1
 
diff --git a/README.md b/README.md
@@ -1,14 +1,46 @@
-# Stopwatch
-[![Elixir CI](https://github.com/dwyl/phoenix-liveview-stopwatch/actions/workflows/ci.yml/badge.svg)](https://github.com/dwyl/phoenix-liveview-stopwatch/actions/workflows/ci.yml)
+<div align="center">
 
+# `Phoenix` `LiveView` _Stopwatch_ ⏱️
 
-- Create new phoenix "barebone" Phonenix application:
+[![GitHub Workflow Status](https://img.shields.io/github/workflow/status/dwyl/phoenix-liveview-stopwatch/Elixir%20CI?label=build&style=flat-square)](https://github.com/dwyl/phoenix-liveview-stopwatch/actions/workflows/ci.yml)
+[![codecov.io](https://img.shields.io/codecov/c/github/dwyl/phoenix-liveview-stopwatch/main.svg?style=flat-square)](http://codecov.io/github/dwyl/phoenix-liveview-stopwatch?branch=main)
+[![Hex.pm](https://img.shields.io/hexpm/v/phoenix?color=brightgreen&style=flat-square)](https://hex.pm/packages/phoenix)
+[![contributions welcome](https://img.shields.io/badge/contributions-welcome-brightgreen.svg?style=flat-square)](https://github.com/dwyl/phoenix-liveview-stopwatch/issues)
+[![HitCount](http://hits.dwyl.com/dwyl/phoenix-liveview-stopwatch.svg)](http://hits.dwyl.com/dwyl/phoenix-liveview-stopwatch)
+
+</div>
+
+## Why? 💡
+
+We wanted to build the **simplest possible _shared_ stopwatch**
+as a self-contained
+[***experiment***](https://github.com/dwyl/technology-stack/issues/96)
+to test how easy complex/simple it would be
+before using this in our main
+[**`app`**](https://github.com/dwyl/app)
+
+## What? 🤷‍♀️
+
+`Phoenix LiveView` lets us build RealTime collaborative apps
+without writing a line of `JavaScript`.
+This is an _example_ that anyone can understand in **`10 mins`**.
+
+## How? 💻
+
+Try the finished app before you try to build it:
+
+https://liveview-stopwatch.fly.dev/
+
+![stopwatch](https://user-images.githubusercontent.com/194400/174432051-5199369d-df07-4809-a758-24d3738535f7.png)
+
+Once you've tried it, come back and **_build_ it**!
+### Create a new "barebones" Phonenix application:
 
 ```sh
 mix phx.new stopwatch --no-mailer --no-dashboard --no-gettext --no-ecto
 ```
 
-- Create folders and files for liveView stopwatch code:
+### Create folders and files for `LiveView`:
 
 ```sh
 mkdir lib/stopwatch_web/live
@@ -18,14 +50,21 @@ mkdir lib/stopwatch_web/templates/stopwatch
 touch lib/stopwatch_web/templates/stopwatch/stopwatch.html.heex
 ```
 
-- Update router. In `lib/stopwatch_web/router.ex` update the "/" endpoint:
+### Update router 
+
+In `lib/stopwatch_web/router.ex` update the "/" endpoint:
 
 ```elixir
 live("/", StopwatchLive)
 ```
 
-- Create liveView logic (mount, render, handle_event, handle_info) 
-in StopwatchLive module. In `lib/stopwatch_web/live/stopwatch_live.ex` add:
+### Create `LiveView` logic 
+
+Create the 
+`mount`, `render`, `handle_event` and `handle_info` 
+functions 
+in StopwatchLive module: 
+`lib/stopwatch_web/live/stopwatch_live.ex` 
 
 ```elixir
 defmodule StopwatchWeb.StopwatchLive do
@@ -76,22 +115,31 @@ Finally the `handle_info` function manages the `:tick` event. If the status is
 `:running` when send another `:tick` event after 1 second and increment the `:timer`
 value with 1 second.
 
-- Update `lib/stopwatch_web/templates/layout/root.hml.heex` with the following body:
+### Update Root Template
+
+Update the 
+`lib/stopwatch_web/templates/layout/root.hml.heex` 
+with the following body:
 
 ```html
 <body>
     <%= @inner_content %>
 </body>
 ```
 
-- Create the `StopwatchView` module in `lib/stopwatch_web/views/stopwatch_view.ex` 
+### Create View
+
+Create the `StopwatchView` module in `lib/stopwatch_web/views/stopwatch_view.ex` 
 
 ```elixir defmodule StopwatchWeb.StopwatchView do
   use StopwatchWeb, :view
 end
 ```
 
-Finally create the templates in `lib/stopwatch_web/templates/stopwatch/stopwatch.html.heex`:
+### Create Template
+
+Finally create the templates in 
+`lib/stopwatch_web/templates/stopwatch/stopwatch.html.heex`:
 
 ```html
 <h1><%= @time |> Time.truncate(:second) |> Time.to_string()  %></h1>
@@ -104,5 +152,257 @@ Finally create the templates in `lib/stopwatch_web/templates/stopwatch/stopwatch
 <% end %>
 ```
 
-If you run the server with `mix phx.server` you should now be able
+If you run the server with 
+`mix phx.server` 
+you should now be able
 to start/stop the stopwatch.
+
+## Sync Stopwatch
+
+So far the application will create a new timer for each client.
+That is good but doesn't really showcase the power of `LiveView`.
+We might aswell just be using _any_ other framework/library.
+To really see the power of using `LiveView`,
+we're going to use its' super power - 
+lightweight websocket "channels" -
+to create a _collaborative_ stopwatch experience!
+
+<!--
+> **Note**: this example will only have a single timer
+> that is shared across multiple clients.
+> It's intended as a simple showcase not a real-world app.
+> Though you could easily use this 
+> as the basis for a reaction-time game
+> that kids could play for _hours_. 
+-->
+
+To be able to sync a timer 
+between all the connected clients 
+we can move the stopwatch logic 
+to its own module and use 
+[`Agent`](https://elixir-lang.org/getting-started/mix-otp/agent.html).
+
+Create `lib/stopwatch/timer.ex` file and add the folowing content:
+
+```elixir
+defmodule Stopwatch.Timer do
+  use Agent
+  alias Phoenix.PubSub
+
+  def start_link(opts) do
+    Agent.start_link(fn -> {:stopped, ~T[00:00:00]} end, opts)
+  end
+
+  def get_timer_state(timer) do
+    Agent.get(timer, fn state -> state end)
+  end
+
+  def start_timer(timer) do
+    Agent.update(timer, fn {_timer_status, time} -> {:running, time} end)
+    notify()
+  end
+
+  def stop_timer(timer) do
+    Agent.update(timer, fn {_timer_status, time} -> {:stopped, time} end)
+    notify()
+  end
+
+  def tick(timer) do
+    Agent.update(timer, fn {timer_status, timer} ->
+      {timer_status, Time.add(timer, 1, :second)}
+    end)
+
+    notify()
+  end
+
+  def subscribe() do
+    PubSub.subscribe(Stopwatch.PubSub, "liveview_stopwatch")
+  end
+
+  def notify() do
+    PubSub.broadcast(Stopwatch.PubSub, "liveview_stopwatch", :timer_updated)
+  end
+end
+```
+
+The agent defines the state of the stopwatch 
+as a tuple `{timer_status, time}`.
+We defined the 
+`get_timer_state/1`, `start_timer/1`, `stop_timer/1` 
+and `tick/1` functions 
+which are responsible for updating the tuple.
+
+Finally the last two funtions: 
+`subscribe/0` and `notify/0` 
+are responsible for listening and sending 
+the `:timer_updated` event via PubSub to the clients.
+
+
+Now we have the Timer agent defined 
+we can tell the application to create
+a stopwatch when the application starts.
+Update the `lib/stopwatch/application.ex` file 
+to add the `StopwatchTimer`
+in the supervision tree:
+
+```elixir
+    children = [
+      # Start the Telemetry supervisor
+      StopwatchWeb.Telemetry,
+      # Start the PubSub system
+      {Phoenix.PubSub, name: Stopwatch.PubSub},
+      # Start the Endpoint (http/https)
+      StopwatchWeb.Endpoint,
+      # Start a worker by calling: Stopwatch.Worker.start_link(arg)
+      # {Stopwatch.Worker, arg}
+      {Stopwatch.Timer, name: Stopwatch.Timer} # Create timer
+    ]
+```
+
+We define the timer name as `Stopwatch.Timer`. 
+This name could be any `atom` 
+and doesn't have to be an existing module name. 
+It is just a unique way to find the timer.
+
+We can now update our `LiveView` logic 
+to use the function defined in `Stopwatch.Timer`.
+Update 
+`lib/stopwatch_web/live/stopwatch_live.ex`:
+
+```elixir
+defmodule StopwatchWeb.StopwatchLive do
+  use StopwatchWeb, :live_view
+
+  def mount(_params, _session, socket) do
+    if connected?(socket), do: Stopwatch.Timer.subscribe()
+
+    {timer_status, time} = Stopwatch.Timer.get_timer_state(Stopwatch.Timer)
+    {:ok, assign(socket, time: time, timer_status: timer_status)}
+  end
+
+  def render(assigns) do
+    Phoenix.View.render(StopwatchWeb.StopwatchView, "stopwatch.html", assigns)
+  end
+
+  def handle_event("start", _value, socket) do
+    Process.send_after(self(), :tick, 1000)
+    Stopwatch.Timer.start_timer(Stopwatch.Timer)
+    {:noreply, socket}
+  end
+
+  def handle_event("stop", _value, socket) do
+    Stopwatch.Timer.stop_timer(Stopwatch.Timer)
+    {:noreply, socket}
+  end
+
+  def handle_info(:timer_updated, socket) do
+    {timer_status, time} = Stopwatch.Timer.get_timer_state(Stopwatch.Timer)
+    {:noreply, assign(socket, time: time, timer_status: timer_status)}
+  end
+
+  def handle_info(:tick, socket) do
+    {timer_status, _time} = Stopwatch.Timer.get_timer_state(Stopwatch.Timer)
+
+    if timer_status == :running do
+      Process.send_after(self(), :tick, 1000)
+      Stopwatch.Timer.tick(Stopwatch.Timer)
+      {:noreply, socket}
+    else
+      {:noreply, socket}
+    end
+  end
+end
+```
+
+In `mount/3`, when the socket is connected 
+we subscribe the client to the PubSub channel. 
+This will allow our `LiveView` 
+to listen for events from other clients.
+
+The  `start`, `stop` and `tick` events 
+are now calling the
+`start_timer`, `stop_timer` and `tick` functions 
+from `Timer`, 
+and we return `{:ok, socket}` 
+without any changes on the `assigns`.
+All the updates are now done 
+in the new 
+`handle_info(:timer_updated, socket)`
+function. 
+The `:timer_updated` event 
+is sent by `PubSub` 
+each time the timer state is changed.
+
+
+If you run the application:
+```sh
+mix phx.server
+```
+
+And open it in two different clients 
+you should now have a synchronised stopwatch!
+
+![liveview-stopwatch-sync](https://user-images.githubusercontent.com/194400/174431168-d37e5382-f3e1-4c99-bd3b-bd3500a5035e.gif)
+
+To _test_ our new `Stopwatch.Timer` agent, 
+we can add the following code to
+`test/stopwatch/timer_test.exs`:
+
+```elixir
+defmodule Stopwatch.TimerTest do
+  use ExUnit.Case, async: true
+
+  setup context do
+    start_supervised!({Stopwatch.Timer, name: context.test})
+    %{timer: context.test}
+  end
+
+  test "Timer agent is working!", %{timer: timer} do
+    assert {:stopped, ~T[00:00:00]} == Stopwatch.Timer.get_timer_state(timer)
+    assert :ok = Stopwatch.Timer.start_timer(timer)
+    assert :ok = Stopwatch.Timer.tick(timer)
+    assert {:running, time} = Stopwatch.Timer.get_timer_state(timer)
+    assert Time.truncate(time, :second) == ~T[00:00:01]
+    assert :ok = Stopwatch.Timer.stop_timer(timer)
+    assert {:stopped, _time} = Stopwatch.Timer.get_timer_state(timer)
+  end
+
+
+  test "Timer is reset", %{timer: timer} do
+    assert :ok = Stopwatch.Timer.start_timer(timer)
+    :ok = Stopwatch.Timer.tick(timer)
+    :ok = Stopwatch.Timer.tick(timer)
+    {:running, time} = Stopwatch.Timer.get_timer_state(timer)
+    assert Time.truncate(time, :second) == ~T[00:00:02]
+    Stopwatch.Timer.reset(timer)
+    assert {:stopped, ~T[00:00:00]} == Stopwatch.Timer.get_timer_state(timer)
+  end
+end
+```
+
+We use the `setup` function 
+to create a new timer for each test.
+`start_supervised!` takes care of creating 
+and stopping the process timer for the tests. 
+Since `mix run` will automatically run the `Timer` 
+defined in `application.ex`, 
+i.e. the Timer with the name `Stopwatch.Timer` 
+we want to create new timers 
+for the tests using other names to avoid conflicts. 
+This is why we use `context.test` 
+to define the name of the test `Timer` process.
+
+
+## What's next?
+
+If you found this example useful, 
+please ⭐️ the GitHub repository
+so we (_and others_) know you liked it!
+
+Your feedback is always very welcome!
+
+If you think of other features
+you want to add,
+please 
+[**open an issue**](https://github.com/dwyl/phoenix-liveview-stopwatch/issues)
+to discuss!