gen.R

library(shiny)
library(shinydashboard)
library(shinythemes)
library(highlight)
library(knitr)
library(rmarkdown)

shinyApp(
  ui = fluidPage(
    title = 'Download a PDF report',
    sidebarLayout(
      sidebarPanel(
        helpText(),
        selectInput('x', 'Build a regression model of mpg against:',
                    choices = names(mtcars)[-1]),
        radioButtons('format', 'Document format', c('PDF', 'HTML', 'Word'),
                     inline = TRUE),
        downloadButton('downloadReport')
      ),
      mainPanel(
        plotOutput('regPlot')
      )
    )
  ),
  server = function(input, output) {
    
    regFormula <- reactive({
      as.formula(paste('mpg ~', input$x))
    })
    
    output$regPlot <- renderPlot({
      par(mar = c(4, 4, .1, .1))
      plot(regFormula(), data = mtcars, pch = 19)
    })
    
    output$downloadReport <- downloadHandler(
      filename = function() {
        paste('my-report', sep = '.', switch(
          input$format, PDF = 'pdf', HTML = 'html', Word = 'docx'
        ))
      },
      
      content = function(file) {
        src <- normalizePath('report.Rmd')
        
        # temporarily switch to the temp dir, in case you do not have write
        # permission to the current working directory
        owd <- setwd(tempdir())
        on.exit(setwd(owd))
        file.copy(src, 'report.Rmd', overwrite = TRUE)
        
        library(rmarkdown)
        out <- render('report.Rmd', switch(
          input$format,
          PDF = pdf_document(), HTML = html_document(), Word = word_document()
        ))
        file.rename(out, file)
      }
    )
  }
)