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React - Shiny Template

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# [React JS 🤝 Shiny] template

[**See the minimalistic DEMO**](https://akkido.shinyapps.io/react_shiny_template/)

## React JS developers - welcome on (dash) board!

This setup allows the user to build frontend in pure **[`React.js`](https://reactjs.org/)** whereas keep the backend/logic in **[`Shiny`](https://shiny.rstudio.com/)**.

But one may ask - why?

1. By breaking the monolithic structure of the `Shiny` app into frontend & backend we are able to apply modern standards and patterns for building beautiful web applications with `React`.
2. `Shiny` wouldn't have to be involved in generating UI.
3. UI part is no longer dependent on R wrappers of JS libraries. 
4. You are able now to take advantage of:
    - [Material UI](https://mui.com/getting-started/usage/), [PrimeReact](https://primefaces.org/primereact/showcase/), [Fluent UI](https://developer.microsoft.com/en-us/fluentui#/controls/web), [React-Bootstrap](), [Blueprint](https://blueprintjs.com/docs/), [Ant Design](https://ant.design/components/overview/) and many other great UI libraries.
    - static typing with [TypeScript](https://www.typescriptlang.org/) ❤️
    - using [JSX](https://reactjs.org/docs/introducing-jsx.html) ❤️
    - [mobx](https://www.mobxjs.com/), [redux](https://redux.js.org/) for state management
    - modern tools for creating your design system/styling `React` components - e.g. [Storybook](https://storybook.js.org/docs/react/get-started/introduction), [styled-components](https://styled-components.com/)
    - solutions addressing performance issues - e.g. [react-virtualized](https://github.com/bvaughn/react-virtualized)/[react-window](https://github.com/bvaughn/react-window) for [rendering huge lists](https://reactjs.org/docs/optimizing-performance.html#virtualize-long-lists)
    - support from large `React` community
    - the best standards of building web applications and patterns
    - (many many others)
5. The `React` app is ultimately built as a static page therefore it can be placed as a static resource in our `Shiny` project (e.g. in `www` folder). It implies that **nothing changes in terms of the deployment e.g. to RStudio Connect**).

### For whom?
  - You are a `Shiny` developer passionate about `React` / willing to apply the latest standards of developing frontend or 
  - You would like to reuse existing components from your other `React` applications or
  - You would like to collaborate with a `React` developer on your `Shiny` dashboard to make it even more awesome

And

- You want to deploy your app the same way as other, regular `Shiny` apps

then **this setup is for you!**

> Otherwise you might be interested in using [`shiny.react`](https://appsilon.github.io/shiny.react/) and packages based on top of that (e.g. [`shiny.fluent`](https://appsilon.github.io/shiny.fluent/)). Here is a nice example of [how to wrap Liquid Oxygen library with `shiny.react`](https://appsilon.github.io/shiny.react/articles/shiny-react.html)

## Setup

The setup allows for:
1. Using [`Node.js` server for the development](https://create-react-app.dev/docs/getting-started/#npm-start-or-yarn-start) (to see changes made live)
2. Building the `React` app as a static page and then using it with `Shiny`

The `React` app itself has been initialized with [`create-react-app`](https://reactjs.org/docs/create-a-new-react-app.html), so in case you need to perform some more sophisticated operations please take a look at the [documentation](https://reactjs.org/docs/getting-started.html)

# Launching the app

1. Make sure you have all the `R` dependencies installed:

``` console
npm run install_shiny
```

> Or from the `Shiny` subfolder
> ``` r
> renv::restore()
> ```

2. Then you launch the `Shiny` app

``` console
npm run prod
```

> Or from the `Shiny` subfolder in an usual way:
>``` r
>shiny::runApp()
>```

# Development
## Starting the development server

> Required `Node.js` 16.x

1. Make sure you have all the `R` dependencies installed:

``` console
npm run install_shiny
```

2. If you are starting the development for the first time you need to install all the `JS` dependencies:

``` console
npm run install_react
```

3. Then you need to start both:
  
      a. the `Node.js` development server:

``` console
      npm run start_react
      ```
      b.  the `Shiny` app:

``` console
     npm run start_shiny
     ```

>If using Linux or MAC OS you can run simply:
  >``` console
  >npm run dev
  >```
    
And you are ready to go!

>Sometimes your development app may behave strange (like restarting the session). Please try to clear the cache (in Chrome by `Shift` + `F5`)

---

Once you decide your `React` app is ready you need to build it and place it inside your `Shiny` project. You can do it by running the command:

``` console
npm run build
```

Now, you can run your `Shiny` app:

``` console
npm run prod
```

> Or from the `Shiny` subfolder in an usual way:
>``` R
>shiny::runApp()
>```

## Communication between `Shiny` and `React`

There are basically three ways how a `React` app can communicate a `Shiny` backend:

1. [`Shiny` → `React` (WebSocket)](#1-shiny--react-websocket)
  2. [`React` → `Shiny` (WebSocket)](#2-react--shiny-websocket)

> You can also learn more about communication between JS and R through websocket [HERE](https://shiny.rstudio.com/articles/communicating-with-js.html)

3. [`React` ⇄ `Shiny` (HTTP API)](#3-react--shiny-http-api)

> **NOTE 1**: no `ui` function is being presented assuming that all the `UI` is being handled by `React` app

> **NOTE 2**: The examples given below aim to present just the rough idea of how the connection could be established (putting aside applicable design patterns or great tools you could use - like [`react-query`](https://react-query.tanstack.com/)).

### 1. `Shiny` → `React` (WebSocket)

#### Example

On the `Shiny` server side:

``` r
library(shiny)

server <- function(input, output, session) {
  #...
  session$sendCustomMessage("message_from_shiny", "HELLO FROM SHINY SERVER!")
}
```

On the `React` side:

``` javascript 
const App = () => {
  const [shinyMessage, setShinyMessage] = useState(null);
  
  window.Shiny.addCustomMessageHandler("message_from_shiny", (msg) => {
    setShinyMessage(msg);
  });
  
  return <p>{shinyMessage}</p>
}
```

### 2. `React` → `Shiny` (WebSocket)

#### Example

On the `Shiny` server side:
``` r
library(shiny)

server <- function(input, output, session) {
  #...
  observeEvent(input$message_from_react, {
    print(input$message_from_react)
  })
}
```

On the `React` side:

``` javascript 
const App = () => {
  const sendMessage = (e) => {
    window.Shiny.setInputValue("message_from_react", e.target.value);
  };
  
  return <input type="text" onChange={sendMessage} />
}
```

### 3. `React` ⇄ `Shiny` (HTTP API)

#### Description

This is probably the least popular way of communicating with `Shiny` server. However, there are many benefits from using it:

1. Thanks to the stateless nature of `HTTP API` you can manage the app state solely in `React` (with a help of e.g. [`mobx`](https://mobx.js.org/), [`redux`](https://redux.js.org/))
2. You don't need to configure two-way WebSocket communication whenever `React` needs anything from `Shiny` (i.e. [approach 1](#1-shiny--react-websocket) combined with [approach 2](#2-react--shiny-websocket))
3. It would be potentially easier to replace `Shiny` with any other `HTTP API` backend

The existence of `HTTP API` in the `Shiny` package given out of the box is a great and promising feature. However, *out of the box* does not actually mean transparent in a sense that the developer must combine certain - not intuitively named or well documented - functions in order to achieve it:

- [`session$registerDataObj(name, data, filterFunc)`](https://shiny.rstudio.com/reference/shiny/latest/session.html)
- [`shiny::httpResponse(status, content_type, content, headers)`](https://shiny.rstudio.com/reference/shiny/latest/httpResponse.html)

##### `session$registerDataObj(name, data, filterFunc)`

> **registerDataObj(name, data, filterFunc)**<br/>
> Publishes any `R` object as a URL endpoint that is unique to this session. `name` must be a single element character vector; it will be used to form part of the URL. `filterFunc` must be a function that takes two arguments: `data` (the value that was passed into `registerDataObj`) and req (an environment that implements the `Rook` specification for HTTP requests). `filterFunc` will be called with these values whenever an HTTP request is made to the URL endpoint. The return value of `filterFunc` should be a `Rook`-style response.

So instead of publishing any R object directly (in our case `data = list()`) we are focusing on the `filterFunc(data, req)` function, which in this case will work as the request handler.

The function returns an URL which looks similarily to this:
> session/13b6edsessiontoken3764158e8a3af1/dataobj/example-api-example-get-api?w=&nonce=14367c50429fc201

##### `shiny::httpResponse(status, content_type, content, headers)`
The response will be handled by function `shiny::httpResponse(...)` - there is no detailed description unfortunately ([yet](https://github.com/rstudio/shiny/issues/3471)), but the idea is pretty straightforward - [see the documentation](https://shiny.rstudio.com/reference/shiny/latest/httpResponse.html). When determining `content_type` you can use [this source](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types)

---

#### Graph

![graph](https://user-images.githubusercontent.com/54677165/142600070-48d240d5-c2ff-43c7-a9bd-166ce11bdd67.png)

---
#### Example
On the `Shiny` server side:

``` r
library(shiny)
library(jsonlite)
library(dplyr)
library(ggplot2)

server <- function(input, output, session) {
  #...
  
  return_data <- ggplot2::midwest
  
  #' Endpoint for getting the data
  example_get_data_url <- session$registerDataObj(
    name = "example-get-api",
    data = list(), # Empty list, we are not sharing any object
    # That's the place where the request is being handled
    filterFunc = function(data, req) {
      if (req$REQUEST_METHOD == "GET") {
        response <- return_data
        response %>%
          toJSON(auto_unbox = TRUE) %>%
          httpResponse(200, "application/json", .)
      }
    }
  )
  
  session$sendCustomMessage(
    "shiny_api_urls",
    list(
      example_get_data_url = example_get_data_url
    )
  )
}
```

On the `React` side:

``` javascript 
const App = () => {
  const [urls, setUrls] = useState(null);
  const [data, setData] = useState([]);
  
  Shiny.addCustomMessageHandler('shiny_api_urls', function(urls) => {
    setUrls(urls);
    fetchData(urls);
  })
  
  const fetchData = async (urls) => {
    const fetchedData = await fetch(urls.example_get_data_url).then(data => data.json());
    setData(fetchedData);
  }
  
  const item_list = data.map((item) => (
    <li key={item.PID}>{`${item.county} (${item.state})`}</li>
  ));

return <ul>{item_list}</ul>
}
```

---

# FAQ

## Why `Shiny` HTTP API approach? What about [`Plumber`](https://www.rplumber.io/)?

1. Plumber doesn’t offer WebSocket connection out of the box yet as `Shiny` does. In other words, with Plumber only the client is initiating a communication - by making a request - whereas Shiny allows for bidirectional initialization. Having that the developer can trigger things to happen from the server-side, e.g. send a notification/message to the browser.

2. As the UI is a static web page **it can be part of the `Shiny` project**. Therefore the developer does not have to bother with separate servers/deployments for backend and frontend. **Deployment process to RStudio Connect will then be the same as for the standard `Shiny` app**. It could be particularly useful for the `Shiny` developers that want to keep their workflow.

3. The session is still managed by `Shiny` (all the HTTP URLs contain a session token, so assuming that session token is secret the HTTP URLs might be considered as session-scoped). `React` app contains all `Shiny` dependencies (through [`{{ headContent() }}`](https://shiny.rstudio.com/articles/templates.html) used in [`htmlTemplate()`](https://shiny.rstudio.com/reference/shiny/latest/htmlTemplate.html) function), so when the session is over you can notice the characteristic grey page and notification about reloading the session.

4. With this approach you can still benefit from `Shiny` reactivity when developing your backend.

At the end of a day - everything depends on the case

# Conclusions

1. There is a possibility to break the monolithic structure of the app into the `Shiny` backend and `React` frontend part.

2. Despite the breakout the `React` app can be still a part of the `Shiny` project implying no need for a separate frontend server.

3. The `React` app can be almost totally independent from `Shiny` (except initial WebSocket-based URL exchange) which:
    - makes the potential backend replacement much easier.
    - allows for concurrent development of the UI (e.g. by `React` developer) and server logic in `Shiny`.

4. Apart from a WebSocket `Shiny` offers session-scoped HTTP API out of the box.

5. Such setup seems to be pretty hard to implement on the existing/grown up projects, so one could consider it when starting a new one.

6. `React` ecosystem offers huge amount of cool features you can use directly in your `Shiny` app!

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