A simple R Shiny app to demonstrate use of reactive values via a gacha-style interface

gachr.R

ui <- bslib::page_fillable(
  bslib::card(
    bslib::card_header("Gacha"),
    shiny::textOutput("rolled_details"),
    shiny::textOutput("rolled_emoji"),
    shiny::actionButton("btn_roll", "Roll!")
  ),
  bslib::card(
    bslib::card_header("Collection"),
    shiny::tableOutput("dex")
  )
)

server <- function(input, output, session) {
  
  emoji_set <- tibble::tribble(
    ~Number, ~Name, ~Image, ~Rarity,
    1L, "Shrimp",  "🦐", "⭐️",
    2L, "Crab",    "🦀", "⭐️",
    3L, "Lobster", "🦞", "⭐️⭐️",
    4L, "Squid",   "🦑", "⭐️⭐️⭐️"
  )
  
  empty_dex <- emoji_set |> 
  dplyr::mutate(
    Name = "<Unknown>",
    Image = "❓",
    Count = 0L
  )
  
  empty_rolled <- tibble::tibble(
    Number = "<Number>",
    Name = "<Name>",
    Image = "❓",
    Rarity = "<Rarity>"
  )
  
  rv <- shiny::reactiveValues(rolled = empty_rolled, dex = empty_dex)
  
  shiny::observeEvent(input$btn_roll, {
    
    emoji_sampled <- emoji_set |> 
    dplyr::mutate(
      Weight = dplyr::case_match(
        Rarity,
        "⭐️" ~ 0.6,
        "⭐️⭐️" ~ 0.3,
        "⭐️⭐️⭐️" ~ 0.1
      )
    ) |> 
    dplyr::slice_sample(n = 1, weight_by = Weight) |> 
    dplyr::select(-Weight)
    
    rv[["rolled"]] <- emoji_sampled
    
    dex_num <- rv[["rolled"]][["Number"]]
    rv[["dex"]][dex_num, "Count"] <- rv[["dex"]][dex_num, "Count"] + 1L
    rv[["dex"]][dex_num, "Name"] <- rv[["rolled"]][["Name"]]
    rv[["dex"]][dex_num, "Image"] <- rv[["rolled"]][["Image"]]
    
  })
  
  output$rolled_details <- shiny::renderText({
    paste0(
      "[", rv[["rolled"]][["Number"]], "] ",
      rv[["rolled"]][["Name"]], " ",
      rv[["rolled"]][["Rarity"]]
    )
  })
  
  output$rolled_emoji <- shiny::renderText(rv[["rolled"]][["Image"]])
  
  output$dex <- shiny::renderTable(rv[["dex"]])
  
}

shiny::shinyApp(ui, server)