Check Splitting Calculator

This is a simple Shiny app that calculates your portion of a check for when you eat out with friends.

#| standalone: true
#| viewerHeight: 600

ui <- fluidPage(
  titlePanel("Check Splitting Calculator"),
  sidebarLayout(
    sidebarPanel(
      textInput("price0",
                label = "Price",
                value = 10),
      actionButton(inputId = "rmv", label = "-"),
      actionButton(inputId = "add", label = "+"),
      textInput("tax",
                label = "Tax Percentage (%)",
                value = 6),
      textInput("tip",
                label = "Tip Percentage (%)",
                value = "15")
    ),
    mainPanel(
      textOutput("finalprice")
    )
  )
)

server <- function(input, output, session) {
  add_rm_counter <- reactiveVal(0)
  
  # add additional text box to insert more prices
  observeEvent(eventExpr = input$add,
               handlerExpr = {
                 add_rm_counter(add_rm_counter() + 1)
                 insertUI(
                   selector = "#rmv",
                   where = "beforeBegin",
                   ui = div(id = paste0("inserttext", add_rm_counter()),
                            textInput(paste0("price", add_rm_counter()),
                                      label = "Another Item")
                   )
                 )
                 
               }
  )
  
  
  # remove text box
  observeEvent(eventExpr = input$rmv,
               handlerExpr = {
                 
                 removeUI(
                   selector = paste0("#inserttext", add_rm_counter())
                 )
                 add_rm_counter(add_rm_counter() - 1)
                 
               }
  )
  
  # price calculation
  total_sum <- reactive(
    sum(
      sapply(
        X = 0:add_rm_counter(),
        FUN = function(i) {
          as.numeric(input[[paste0("price", i)]])
        }
      ),
      na.rm = TRUE
    )
  )
  
  multiplier <- reactive(1 + (0.01*(as.numeric(input$tax)+as.numeric(input$tip))))

  total_price <- reactive(total_sum()*multiplier())
  
  # final output for the total price
  output$finalprice <- renderText(
    if (is.na(multiplier())) {
      paste("Make sure the tax and tip fields are numeric.")
    } else {
      paste("You owe", total_price(), "dollars.", sep = " ")
    }
  )
  
}

shinyApp(ui = ui, server = server)