---
title: "Debug a shiny app with {boomer}"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Debug a shiny app with {boomer}}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r, include = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)
```

We propose a very experimental feature to debug shiny apps, it's still brittle
but we decided to release anyway as it might be useful as is.

You'll need the code of a shiny app saved in a proper project, and the module structure
of the shiny app should follow the recommendations of Hadley Wickham's book
"Mastering Shiny". 

Under these assumptions following `boomer::boom_shinyApp()` is a drop in replacement
for `shiny::shinyApp()`, running your app with enhanced debugging features.

For instance taking an example from "Mastering Shiny", we can
create a file (it needs to be saved in the project!) and fill it with :

```r
histogramUI <- function(id) {
  tagList(
    selectInput(NS(id, "var"), "Variable", choices = names(mtcars)),
    numericInput(NS(id, "bins"), "bins", value = 10, min = 1),
    plotOutput(NS(id, "hist"))
  )
}

histogramServer <- function(id) {
    moduleServer(id, function(input, output, session) {
      data <- reactive(mtcars[[input$var]])
      output$hist <- renderPlot({
        hist(data(), breaks = input$bins, main = input$var)
      }, res = 96)
    })
}

ui <- fluidPage(
  histogramUI("hist1")
)
server <- function(input, output, session) {
  histogramServer("hist1")
}
```

Then after making sure everything is loaded (you might call `devtools::load_all()`
in a package project), we can call `boom_shinyApp(ui, server)` and we get the
following app :

![](shiny-1.png){width=600}


We see the same app as we would with `shiny::shinyApp()` except it's nested into
an "app" tab and we have an additional "boomer log options tab", lets take a look:

![](shiny-2.png){width=600}

In this additional tab we can tick which reactives we want to make verbose.

In our example  we defined two reactives in `histogramServer()` : `data` and `output$hist`, if we tick
`histogramServer/output$hist <- renderPlot(...)` and select anything that triggers
an actualization of the reactive (i.e. that changes the plot) we will observe 
verbose output in the console. 

For instance if we set the number of bins to 15 we will see:

![](shiny-3.png){width=600}


We hope that this can save developers from the chore of running and stopping apps repeatedly
with different variations of debugging code cluttered in various places.