ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(

      sliderInput(inputId = "plot_num", 
                  label = "Number of Plots:", 
                  min = 1, max = 20, value = 5),
            
      sliderInput(inputId = "n_obs", 
                  label = "Number of observations:", 
                  min = 10, max = 500, value = 100),
      
      shiny::radioButtons('slick_type',
                          label = 'Carousel Type',
                          choices = c('single','stack','synch'),
                          selected = 'single',
                          inline = TRUE),
      
      shiny::verbatimTextOutput('current')
    ),
    mainPanel(
      
      slickROutput("slick_output",width='100%',height='200px')
      
      )
  )
)

server <- function(input, output) {

# Create content for the carousel
  
plots <- eventReactive(c(input$n_obs,input$plot_num),{
  
replicate(input$plot_num,{

     xmlSVG({hist(rnorm(input$n_obs),
                  col = 'darkgray',
                  border = 'white')},
            standalone=TRUE)

     },simplify = FALSE)
})

# renderSlickR (We create the slickR objects here)

  output$slick_output <- renderSlickR({
    
    x <- slickR(plots(),
                slideId = 'slick1',
                height = 600,
                width = '50%') + 
      settings(slidesToShow=3,centerMode=TRUE)

    y <- slickR(plots(),
                slideId = 'slick2',
                height = 600,
                width = '50%') + 
      settings(slidesToShow=3,centerMode=TRUE)    
    
    switch(input$slick_type,
           'single' = x,
           'stack'  = x %stack% y,
           'synch'  = x %synch% y
           )

  })
  
# Observe the active slick
  
# The htmlwidget is observed by shiny and information can be retrieved. 

# Using the output name you set for the `renderSlick` object in this example
# it is `output$slick_output`
 
# Using this you can interact server-side "on click" of the active carousel
# by accessing elements in `input$slick_output_current$`

# `.clicked`   : The index of the clicked element|
# `.relative_clicked`: The relative position of the clicked element|
# `.center`    : The index of the center element|
# `.total`     : The total number of elements in the carousel|
# `.active`    : The ID of the active carousel|

# We will store this information in a new reactive environment
active_slick <- shiny::reactiveValues()
  
shiny::observeEvent(input$slick_output_current,{
    active_slick$clicked    <- input$slick_output_current$.clicked
    active_slick$relative_clicked <- input$slick_output_current$.relative_clicked
    active_slick$center     <- input$slick_output_current$.center
    active_slick$total      <- input$slick_output_current$.total
    active_slick$active     <- input$slick_output_current$.slide
})

# Show in the UI the values in active_slick

output$current <- renderText({
  l <- unlist(shiny::reactiveValuesToList(active_slick))
  paste(gsub('_',' ', names(l)), l, sep=' = ', collapse='\n')
})

}

shinyApp(ui = ui, server = server)