distinguish links and nodes in sankeyPlot using event_data

I am building a sankey plot using plotly package with R within a Shiny application.
At some point, I use event_data function which returns an index pointNumber which is an integer ranging from 0 to the number of pairwise nodes relationships.
When performing sankeyPlot in plotly you have to specify the node and link arguments. The problem is that pointNumber provides an index which I cannot distinguish between the node or the link.
I would like the app could identify if the user clicks on a node or on a link.

Here is a toy example. Note that when clicking on node "A", pointNumber returns 0, and the same when clicking on link connecting node "A" and node "B".

library(plotly); library(shiny)
ui <- fluidPage(
  plotlyOutput("plot"),
  verbatimTextOutput("index")
)
server <- function(input, output){
  output$index <- renderPrint({
    event_data("plotly_click", source="sankeyPlot")
  })
  output$plot <- renderPlotly({
    plot_ly(
      source = "sankeyPlot",
      type = "sankey",
      arrangement = "fixed",
      node = list(label = c("A","B","C","D"), hoverinfo="none"),
      link = list(source=c(0,0,1,2), target=c(1,2,3,3), value=c(2,5,2,1), hoverinfo="none")
    )
  })
}
shinyApp(ui, server)

sankey プロットで event_data("plotly_click") を使用する toy Shiny 例から始め、ノードとリンクのクリックに対して返される pointNumber を調べます。sankeyPlot イベントがどのように表現されるかを追跡し、返されるデータによってクリックされた要素をどのように区別できるかを判断します。アプリがクリックの対象がノードかリンクかを確実に識別できれば完了です。