How to prompt user for directory to save download to using ggplot2 in R shiny?

Some ideas come in mind, the first one is to use textInput to specify the folder path to save the plots (~ means the home directory). Alternatively we can use selectInput for pre-specified directories for the user to choose. And finally some kind of pop up or message to notify the user that the plots were saved correctly in case then don't have acces to R's terminal.

Inside the ui.

textInput('path', 'Enter Path for ggsave',value = '~')

Inside the server.

observeEvent(input$download, {
  lapply(1:nplots(), function(i){
    ggsave(
      paste0("vector",i,".png"), 
      plot(mydata()[[i]]),path = input$path
    ) # close ggsave
  }) # close lapply and embedded function
}, ignoreInit = TRUE)

In the end, I had much difficulty with adapting the multi-file download function such that the user can easily specify where to save the files. Thus I instead opted for a modal dialog using the native function downHandler, allowing the user to select which file to download and where to download that file to. downloadHandler does a very nice job of defaulting to the download directory and prompting the user with where to save the file. Below is MWE for this solution (which deviates from my original question but which in the end is a better approach in my view):

library(shiny)
library(shinyMatrix)
library(shinyjs)
library(DT)

matrix1.input <- function(x){
  matrixInput(x, 
              value = matrix(c(0.2), 2, 1, dimnames = list(c("A","B"),NULL)),
              rows = list(extend = FALSE,  names = TRUE),
              cols = list(extend = FALSE, names = FALSE, editableNames = FALSE),
              class = "numeric")}

matrix2.input <- function(x,y,z){
  matrixInput(x,
              value = matrix(c(y,z),1,2,dimnames=list(NULL,c("Y","Z"))),
              rows = list(extend = TRUE,  names = FALSE),
              cols = list(extend = FALSE, names = TRUE, editableNames = FALSE),
              class = "numeric")}  

matrix.validate <- function(x,y){
  a <- y        
  a[,1][a[,1]>x] <- x 
  b <- diff(a[,1,drop=FALSE]) 
  b[b<=0] <- NA               
  b <- c(1,b)                 
  a <- cbind(a,b)
  a <- na.omit(a) 
  a <- a[,-c(3),drop=FALSE]         
  return(a)}

vector.base <- function(x,y){
  a <- rep(y,x) 
  b <- seq(1:x) 
  c <- data.frame(x = b, y = a) 
  return(c)}

vector.multi <- function(x,y,z){                                            
  a <- rep(NA, x)
  a[y] <- z       
  a[seq_len(min(y)-1)] <- a[min(y)] 
  if(max(y) < x){a[seq(max(y)+1, x, 1)] <- 0}   
  a <- approx(seq_along(a)[!is.na(a)],a[!is.na(a)],seq_along(a))$y  
  b <- seq(1:x)                                                     
  c <- data.frame(x = b, z = a)                                     
  return(c)}

vector.multiFinal <- function(x,y){
  vector.multi(x,matrix.validate(x,y)[,1],matrix.validate(x,y)[,2])}

matrix.link <- function(x,y){
  observeEvent(input$periods|input$base_input,{
    updateMatrixInput(session,x,value=matrix(c(input$periods,y),1,2,dimnames=list(NULL, c("y","z"))))})}

ui <- 
  pageWithSidebar(
    headerPanel("Model"),
    sidebarPanel(uiOutput("Panels")),
    mainPanel(
      tabsetPanel(
        tabPanel("Dynamic", value=2,
                 actionButton('showVectorPlotBtn','Vector plots'),
                 actionButton('showVectorValueBtn','Vector values'),
                 
                 actionButton("showDownload", "Download"),
                 
                 uiOutput("vectorTable")),
        id = "tabselected")
    ) # close main panel
  ) # close page with sidebar

server <- function(input,output,session)({
  periods       <- reactive(input$periods)
  base_input    <- reactive(input$base_input)
  vector1_input <- reactive(input$vector1_input)
  vector2_input <- reactive(input$vector2_input)
  yld           <- reactiveValues()
  
  vectorVariable <- function(x,y){
    if(input$showVectorBtn == 0) vector.base(input$periods,x)
    else vector.multiFinal(input$periods,matrix.validate(input$periods,y))}
  
  output$Panels <- renderUI({
    tagList( 
      conditionalPanel(
        condition="input.tabselected==2",
        sliderInput('periods','',min=1,max=120,value=60),
        matrix1.input("base_input"),
        useShinyjs(),
        actionButton('showVectorBtn','Show'), 
        actionButton('hideVectorBtn','Hide'),
        actionButton('resetVectorBtn','Reset'),
        hidden(uiOutput("Vectors"))))})
  
  renderUI({
    matrix.link("vector1_input",input$base_input[1,1])
    matrix.link("vector2_input",input$base_input[2,1])})
  
  output$Vectors <- renderUI({input$resetVectorBtn
    tagList(matrix2.input("vector1_input",input$periods,input$base_input[1,1]),
            matrix2.input("vector2_input",input$periods,input$base_input[2,1]))})
  
  observeEvent(input$showVectorBtn,{shinyjs::show("Vectors")})
  observeEvent(input$hideVectorBtn,{shinyjs::hide("Vectors")})
  
  output$graph1 <- renderPlot(plot(vectorVariable(input$base_input[1,1],vector1_input())))
  output$graph2 <- renderPlot(plot(vectorVariable(input$base_input[2,1],vector2_input())))
  
  output$download <- downloadHandler(
    filename = function() {
          if (input$downloadItem == "Vector2 plot") {paste("Vector2Plot","png",sep=".")}
          else if (input$downloadItem == "Vector values") {paste("vectorValues","csv",sep=".")}
          else {paste("Vector1Plot","png",sep=".")}
      },
    content = function(file){
      
      if(input$downloadItem == "Vector2 plot"){
        png(file)
        plot(vectorVariable(input$base_input[2,1],vector2_input()))
        dev.off()
        } # close if statement
      
      else if(input$downloadItem == "Vector values"){write.csv(vectorsAll(),file,row.names=FALSE)}
      
      else {
        png(file)
        plot(vectorVariable(input$base_input[1,1],vector1_input()))
        dev.off()
        } # close else
      } # close content function
  ) # close download handler
  
  observeEvent(input$showDownload,
               {showModal(modalDialog(
                   selectInput("downloadItem","Select item to download:",
                               c("Vector1 plot","Vector2 plot","Vector values","Card asset amortization values")),
                   downloadButton("download", "Download")
                 
                 ) # close modalDialog
                ) # close showModal
               } # close showModal function
  ) # close observeEvent
  
  output$table1 <- renderDT({vectorsAll()})
  
  observeEvent(input$showVectorPlotBtn,{yld$showme <- tagList(plotOutput("graph1"), plotOutput("graph2"))},ignoreNULL = FALSE)
  observeEvent(input$showVectorValueBtn,{yld$showme <- DTOutput("table1")})
  
  output$vectorTable <- renderUI({yld$showme})
  
  vectorsAll <- reactive({
    cbind(1:periods(),
          vectorVariable(input$base_input[1,1],vector1_input())[,2],
          vectorVariable(input$base_input[2,1],vector2_input())[,2])})})

shinyApp(ui, server)