shiny-module.R

### shiny module that implements the state machine ###

#' Run a quiz in 'shiny'
#'
#' @description A 'shiny' module to implement a quiz. These are the core functions to implement the quiz with a 'shiny' application.
#'
#' @param quiz an object of class `quiz`. See [create_quiz()]
#' @author Joseph Marlo
#' @export
#' 
#' @seealso [create_quiz()] [preview_app()]
#' 
#' @examplesIf interactive()
#' quiz <- create_quiz(
#'   create_question(
#'     'Lorem ipsum dolor sit amet, consectetur adipiscing elit. Select nulla.',
#'     add_choice('auctor'),
#'     add_choice('nulla', correct = TRUE)
#'   ),
#'   create_question(
#'     'Mauris congue aliquet dui, ut dapibus lorem porttitor sed. Select 600.',
#'     add_choice('600', correct = TRUE),
#'     add_choice('800')
#'   )
#' )
#' 
#' ui <- shiny::fluidPage(
#'   htmltools::div(
#'     style = "max-width: 700px",
#'     quiz_ui(quiz)
#'    )
#'  )
#' server <- function(input, output, session) {
#'  quiz_server(quiz)
#' }
#' shinyApp(ui, server)
#' @describeIn quiz_ui UI side function
quiz_ui <- function(quiz){
  
  verify_quiz_structure(quiz)
  ns <- quiz@options$ns

  htmltools::tagList(
    add_external_resources(),
    htmltools::div(
      id = ns('quiz-container'),
      class = 'quiz-container',
      shiny::uiOutput(outputId = ns('UI_quiz'))
    )
  )
}

#' @param quiz an object of class `quiz`. See [create_quiz()]
#' @export
#' @return a reactive object showing the current results of the quiz
#' 
#' @describeIn quiz_ui Server side function
quiz_server <- function(quiz){
  
  verify_quiz_structure(quiz)
  ns <- quiz@options$ns
  id <- ns(NULL)
  if (!isTRUE(stringr::str_count(id, '-') <= 1)) cli::cli_abort('namespace id is invalid. Too many hyphens. Remove any hyphens in your id. Otherwise, are you trying to nest modules more than two deep?')
  id <- stringr::str_remove_all(id, "^.*?-") # remove any prefixes due to parent modules; this is fragile but works
  
  shiny::moduleServer(id, function(input, output, session){

    # add css class to the quiz container
    if (is_truthy(quiz@options$class)) shinyjs::addClass(id = 'quiz-container', class = quiz@options$class)
    
    # add headers to question texts
    quiz <- sm_ui_format_prompts(quiz)
    
    # set the current state and potential values
    store <- sm_create_reactive_store(quiz)
    
    # reset quiz
    shiny::observeEvent(input$restart_button, {
      
      # reset the state to the first question
      store <- sm_set_state(store, variable = 'current-state', value = 'quiz-question-1')
      
      # remove any responses
      store$questions <- quiz@questions
      store <- sm_set_state(store, variable = 'quiz-skipped', value = FALSE)
      store$is_correct <- rep(NA, length(quiz@questions))
    })
    
    # skip quiz / finish quiz
    shiny::observeEvent(input$skip_button, {
      store <- sm_set_state(store, variable = 'current-state', value = 'quiz-complete')
      store <- sm_set_state(store, variable = 'quiz-skipped', value = TRUE)
    })
    
    # control state behavior
    shiny::observeEvent(store$state, {
      
      # scroll to top of quiz container
      scroll_to_div(ns = ns, id = 'quiz-container')
      
      # state behavior
      if (store$state == 'quiz-complete'){
        # determine the UI
        store$ui_html <- sm_ui_quiz_complete(
          store,
          ns = ns,
          messages = quiz@options$messages
        )

      } else {
        # determine the UI
        store$ui_html <- sm_ui_question(store, ns = ns)
      }
    })
    
    # on button submit, record answer and change the state
    shiny::observeEvent(input$submit_button, {
      
      # disable submit button to prevent double clicks
      shinyjs::disable(id = 'submit_button')
      
      # scroll to top of quiz container
      scroll_to_div(ns = ns, id = 'quiz-container')
      
      # record answers
      store <- sm_set_state(store, variable = 'current-response', value = input$answers)
      
      # is the answer correct and record it
      is_correct <- sm_is_current_correct(store)
      store <- sm_set_state(store, 'current-correct', is_correct)
      
      # grade it
      delay_in_ms <- 2000
      if (is_correct){
        # add UI indicator
        add_checkmark(ns = ns, id = 'quiz-container')
        
        # change the state
        shinyjs::delay(delay_in_ms, {
          new_state <- sm_get_state(store, variable = 'next-state')
          store <- sm_set_state(store, variable = 'current-state', value = new_state)
        })
        
      } else {
        # add UI indicator
        add_red_x(ns = ns, id = 'quiz-container')
        
        # change the state
        # depending on options, go to next question otherwise end here
        shinyjs::delay(delay_in_ms, {
          if (sm_logic_end_on_first_wrong(store)){
            store <- sm_set_state(store, variable = 'current-state', value = 'quiz-complete')
          } else {
            new_state <- sm_get_state(store, variable = 'next-state')
            store <- sm_set_state(store, variable = 'current-state', value = new_state)
          }
        })
      }
    })
    
    # render the UI
    output$UI_quiz <- shiny::renderUI(store$ui_html)
    
    # return the quiz summary
    return(shiny::reactive(sm_summary(store, quiz)))
  })
}

#' External resources to include in the app 
#'
#' Examples include `shinyjs::useShinyjs` or `fontawesome::fa_html_dependency`. These objects are raised to the head of html document.
#'
#' @return an invisible object of class shiny.tag
#' @noRd
#' @author Joseph Marlo
add_external_resources <- function(){
  htmltools::tags$head(
    shinyjs::useShinyjs(),
    fontawesome::fa_html_dependency(),
    htmltools::includeCSS(system.file('shinyquiz.css', package = "shinyquiz")),
  )
}