Single file app which takes various GET parameters and returns the appropriate date boxes (see below for link to blog post)

app.R

library(shiny)
library(lubridate)

server = function(input, output, session){
  
  # type = date rolling n months, quarters
  
  output$dateControls <- renderUI({
    
    query <- parseQueryString(session$clientData$url_search)
    
    ### this is the type check for date
    
    if(!is.null(query$type)){ # check that type exists at all 
      
      if(query$type == "date"){
        
        if(!is.null(query$begin)){
          
          if(!is.na(dmy(query$begin))){
            
            begin = dmy(query$begin)
          } else {
            
            begin = Sys.Date() - 365
          }
        } else {
          
          begin = Sys.Date() - 365
        } 
        
        if(!is.null(query$ending)){
          
          if(!is.na(dmy(query$ending))){
            
            ending = dmy(query$ending)
          } else {
            
            ending = Sys.Date()
            
          }
        } else {
          
          ending = Sys.Date()
        }
        
        return(dateRangeInput("dateRange", label = "Date range",
                              start = begin,
                              end = ending,
                              startview = "year"))
        
      } # end check for type = "date"
      
      ### this is the type check for "rolling"
      
      if(query$type == "rolling"){
        
        if(!is.null(query$window)){
          
          begin = floor_date(now() - months(as.numeric(query$window)), "month")
          
          ending = floor_date(now(), "month") - 1
          
        } else {
          
          begin = Sys.Date() - 365
          
          ending = Sys.Date()
        }
        
        return(dateRangeInput("dateRange", label = "Date range",
                              start = begin,
                              end = ending,
                              startview = "year"))
      } # end check type = "rolling"
      
      if(query$type == "quarter"){
        
        # use Q1/ 2 and Y1/ 2 as variables
        
        if(!is.null(query$Q1) & !is.null(query$Y1)){
          
          # produce vector of every date ever
          
          Q1 = as.numeric(query$Q1)%% 4 + 1
          
          Y1 = as.numeric(query$Y1)
          
          if(Q1 == 1){
            
            Y1 = Y1 + 1
          }
          
          whichDate1 = quarter(seq(as.Date("2009-04-01"), Sys.Date(), by = "day"), 
                               with_year = TRUE) == as.numeric(paste0(Y1, ".", Q1))
          
          theDates1 = seq(as.Date("2009-04-01"), Sys.Date(), by = "day")[whichDate1]
          
          # pick the dates you want
          
          begin = min(theDates1)
          
        } else {
          
          begin = Sys.Date() - 365
        }
        
        if(!is.null(query$Q2) & !is.null(query$Y2)){
          
          # produce vector of every date ever
          
          Q2 = as.numeric(query$Q2)%% 4 + 1
          
          Y2 = as.numeric(query$Y2)
          
          if(Q2 == 1){
            
            Y2 = Y2 + 1
          }
          
          whichDate2 = quarter(seq(as.Date("2009-04-01"), Sys.Date(), by = "day"), 
                               with_year = TRUE) == as.numeric(paste0(Y2, ".", Q2))
          
          theDates2 = seq(as.Date("2009-04-01"), Sys.Date(), by = "day")[whichDate2]
          
          # pick the dates you want
          
          ending = max(theDates2)
          
        } else {
          
          ending = Sys.Date()
        }
        
        return(dateRangeInput("dateRange", label = "Date range",
                              start = begin,
                              end = ending,
                              startview = "year"))
        
      } # end check for quarterly report
      
    } else { # end check does query$type exist
      
      # if query doesn't exist just draw the interface
      
      return(dateRangeInput("dateRange", label = "Date range",
                            start = Sys.Date() - 365,
                            end = Sys.Date(),
                            startview = "year"))
      
    }
    
  })
  
  # fetch the GET STRING
  
  output$queryText <- renderText({
    
    query <- parseQueryString(session$clientData$url_search)
    
    paste(names(query), query, sep = "=", collapse=", ")
    
  })
}

ui = shinyUI(pageWithSidebar(
  
  # Application title
  headerPanel("Survey results- custom search"),
  
  # first set up All/ Division results
  
  sidebarPanel(
    
    # date range
    
    uiOutput("dateControls")
  ),
  
  # tabbed output, stacked plot, trend plot, and responses
  
  mainPanel(
    h3(textOutput("Results")),
    textOutput("queryText")
  )
  
))

shinyApp(ui = ui, server = server)

There's a blog post about this code here