peer_evaluation.R

# peer evaluation app functions =====

#' Set up a peer evaluation app
#' 
#' This functions makes it easy to setup a peer evaluation app folder. It creates the app script \code{app.R} and copies the \code{roster_file} (an Excel spreadsheet) as well as the necessary google access key file for the \code{data_gs_title} google spreadsheet to the same directory. The provided \code{gs_key_file} must grant access to the google spreadsheet (\code{data_gs_title}). See the \href{https://tbltools.kopflab.org/articles/peer_evaluations.html}{peer evaluations vignette} for details on how to set up google credentials and generate a key file. Unless \code{check_gs_access = FALSE}, this function will call the \code{\link{tbl_check_gs_access}} function to confirm that the key file works and provides access to the requested google spreadsheet. Both \code{app.R} and the \code{roster_file} can be edited and tested in the app directory before uploading the whole app to a shiny server. On the shiny server, the \code{roster_file} will be read-only and all actual data will be stored in the google spreadsheet data file.
#' 
#' Use \link{tbl_test_peer_evaluation} with the same \code{folder} as parameter to test run the peer evaluation application locally on your computer. It is recommended to always test the peer evaluation application locally before uploading it to the shiny application server.
#' 
#' Use \link{tbl_duplicate_peer_evaluation} to create a copy of an existing peer evaluation rather than setting one up from scratch. Note that older peer evaluations that don't have a \code{gs_key_file} yet will require this parameter to be set.
#' 
#' @param folder target folder where to setup the peer evaluation (path must be either relative to the current working directory or an absolute file path on the operating system). If the folder does not exist yet, it will be created automatically.
#' @param data_gs_title name of the google spreadsheet that should be used for storing the peer evaluation data. This spreadsheet must already exist and the \code{gs_key_file} must grant access to it.
#' @param template_roster_file path to an excel (.xslx) file that contains the student roster information to use as template for the peer evaluation app (can be edited later)  - will use the package template by default
#' @param gs_key_file path to your .json access key file for peer evaluation google spreadsheets. See the \href{https://tbltools.kopflab.org/articles/peer_evaluations.html}{peer evaluations vignette} for details. This key file is safe to use on a secure shiny app server but be careful to never post this file anywhere publicly as it could be used to gain access to your peer evaluation spreadsheets. Make sure to share the google spreadshhet for this peer evaluation with the \code{client_email} listed in the key file.
#' @param overwrite whether to overwrite the app in the target directory if it already exists
#' @param check_gs_access whether to confirm google spreadsheet access (using the \code{\link{tbl_check_gs_access}} function). Note that if this is set to \code{FALSE}, this function will NOT validate the \code{gs_key_file} and NOT check that the provided \code{data_gs_title} is a valid spreadsheet the key file grants access to.
#' @param gs_token deprecated in favor of using a gs_key_file
#' @return returns the \code{folder} invisibly for ease of use in pipelines
#' @family peer evaluation functions
#' @export
tbl_setup_peer_evaluation <- function(
  folder = "peer_evaluation", data_gs_title = "Peer Evaluation", 
  template_roster_file = system.file(package = "tbltools", "extdata", "roster_template.xlsx"), 
  gs_key_file = NULL, gs_token = deprecated(), overwrite = FALSE, check_gs_access = TRUE) {
  
  # inform user about gs_token deprecation
  if (lifecycle::is_present(gs_token)) 
    lifecycle::deprecate_stop("0.6.0", "tbltools::tbl_setup_peer_evaluation(gs_token = )", "tbltools::tbl_setup_peer_evaluation(gs_key_file = )")
  
  # check for folder
  if(!dir.exists(folder)) {
    glue("Info: creating app directory '{folder}'") %>% message()
    dir.create(folder, recursive = TRUE)
  } else if (file.exists(file.path(folder, "app.R"))) {
    glue("Info: an app already exists in folder '{folder}' ",
         "{if(overwrite) 'but will be overwritten' else '(use \"overwrite = TRUE\" to overwrite)'}") %>% 
      message()
    if (!overwrite) return(invisible(folder))
  }
  
  # process key file
  gs_key_file_save_path <- file.path(folder, "gs_key_file.json")
  no_key_file_msg <- "If you don't want to check access now and copy a key file to your peer evaluation app manually later, set 'gs_key_file = NULL' and 'check_gs_access = FALSE'."
  if (!is.null(gs_key_file)) {
    # check that the file exists
    if (!file.exists(gs_key_file))
      glue("key file does not exist at location '{gs_key_file}', do you have the correct path? ", no_key_file_msg) %>% 
        stop(call. = FALSE)
    
    # check that the file is a valid json file
    tryCatch(
      jsonlite::read_json(gs_key_file),
      error = function(e) {
        glue("key file is not valid JSON, error: ", e$message) %>% 
          stop(call. = FALSE)
      }
    )
    
    # check gs access with key file
    if (check_gs_access) {
      tbl_check_gs_access(data_gs_title = data_gs_title, gs_key_file = gs_key_file)
    }
    
    # copy key file
    glue("Info: copying service account key file to {gs_key_file_save_path}") %>% message()
    file.copy(gs_key_file, to = gs_key_file_save_path) 
  } else if (is.null(gs_key_file) && check_gs_access) {
    glue("cannot check google spreadsheet access without a 'gs_key_file'. ", no_key_file_msg) %>% 
      stop(call. = FALSE)
  }

  # check for roster file
  if(!file.exists(template_roster_file))
    glue("roster file '{template_roster_file}' does not exist") %>% stop(call. = FALSE)
  
  # try to read roster file
  tryCatch(roster <- read_excel(template_roster_file), error = function(e) {
    glue("could not read roster Excel file '{template_roster_file}': {e$message}") %>% 
    stop(call. = FALSE)
  })
  
  # copy roster file
  if (!file.exists(file.path(folder, "roster.xlsx")) || overwrite) {
    glue("Info: copying '{basename(template_roster_file)}' to {folder}/roster.xlsx") %>% message()
    file.copy(template_roster_file, to = file.path(folder, "roster.xlsx"), overwrite = TRUE)
  }
  
  # check roster file
  check_student_roster(roster)

  # generate function call
  glue("Info: creating {folder}/app.R application file and application content") %>% message()
  
  # md template files
  system.file(package = "tbltools", "extdata", "app_template_files") %>% 
    list.files(pattern = "*\\.md$", full.names = TRUE, include.dirs = FALSE, recursive = TRUE) %>% 
    file.copy(to = folder, overwrite = TRUE)
  
  if (!dir.exists(file.path(folder, "www"))) dir.create(file.path(folder, "www"))
  system.file(package = "tbltools", "extdata", "app_template_files", "www", "app.css") %>% 
    file.copy(to = file.path(folder, "www"), overwrite = TRUE)
  
  # generate function call parameters ======
  parameters <- 
    list(
      data_gs_title = data_gs_title,
      app_title = "Peer Evaluation",
      points_per_teammate = 10,
      min_points = 0,
      max_points = 15,
      min_point_difference = 2
    ) %>% {
      map2_chr(names(.), ., function(var, val) {
        val <- 
          if(is_quosure(val)) quo_text(val)
          else if (is.null(val)) "NULL"
          else if(is.numeric(val) || is.logical(val)) val
          else if (is.character(val)) str_c("\"", val, "\"")
          else stop("don't know how to process ", class(val))
        str_c(var, " = ", val)
      })
    } %>% 
    glue::glue_collapse(sep = ",\n\t")
    
  glue(
    "library(tbltools)",
    "tbl_run_peer_evaluation(",
    "  {parameters}",
    ")", .sep = "\n") %>% 
    cat(file = file.path(folder, "app.R"))
  
  # copy evaluation template
  glue("Info: creating {folder}/evaluation.Rmd evaluation file") %>% message()
  
  system.file(package = "tbltools", "extdata", "evaluation_template.Rmd") %>% 
    read_lines() %>% 
    glue::glue_collapse(sep = "\n") %>% 
    str_interp(list(data_gs_title = data_gs_title)) %>% 
    cat(file = file.path(folder, "evaluation.Rmd"))
  
  glue("Info: set up of tbltools' Peer Evaluation app in directory '{folder}' is complete.",
       "Please modify the files in '{folder}' as appropriate and ",
       "run tbl_test_peer_evaluation('{folder}') before before uploading to shiny server.") %>% 
    message()
  
  return(invisible(folder))
}

#' Duplicate a peer evaluation app
#' 
#' This functions makes it easy to duplicate an existing peer evaluation by copying all relevant files into a new folder. You can optionally change the google spreadsheet the new peer evaluation is linked to by specifying the \code{data_gs_title} parameter. To create a new peer evaluation from scratch, use \link{tbl_setup_peer_evaluation} instead. 
#' 
#' @param template folder where the existing peer evaluation that is to be duplicated is located (path must be either relative to the current working directory or an absolute file path on the operating system).
#' @param folder target folder where to setup the duplicated peer evaluation (path must be either relative to the current working directory or an absolute file path on the operating system). If the folder does not exist yet, it will be created automatically.
#' @inheritParams peer_evaluation_server
#' @inheritParams tbl_setup_peer_evaluation
#' @return returns the \code{folder} invisibly for ease of use in pipelines
#' @family peer evaluation functions
#' @export
tbl_duplicate_peer_evaluation <- function(template = "peer_evaluation", folder = "peer_evaluation2", data_gs_title = NULL, overwrite = FALSE, check_gs_access = TRUE) {
  
  # check old folder
  check_peer_evaluation_folder(template)
  
  # check new folder
  if(!dir.exists(folder)) {
    glue("Info: creating app directory '{folder}'") %>% message()
    dir.create(folder, recursive = TRUE)
  } else if (file.exists(file.path(folder, "app.R"))) {
    glue("Info: an app already exists in folder '{folder}' ",
         "{if(overwrite) 'but will be overwritten' else '(use \"overwrite = TRUE\" to overwrite)'}") %>% 
      message()
    if (!overwrite) return(invisible(folder))
  }
  
  # copy files
  files <- list.files(template, all.files = TRUE, recursive = TRUE, full.names = TRUE)
  glue("Info: copying {length(files)} files from template '{template}' into '{folder}'...") %>% 
    message()
  purrr::map(files, file.copy, to = folder, overwrite = TRUE)
  
  # find data gs title
  app_lines <- readr::read_lines(file = file.path(folder, "app.R"))
  old_data_gs_title_line <- stringr::str_detect(app_lines, "data_gs_title")
  if (sum(old_data_gs_title_line) != 1) {
    stop("could not identify where in the app.R file the 'data_gs_title' parameter is located", call. = FALSE)
  }
  
  if (!is.null(data_gs_title)) {
    # switching to new title
    glue("Info: changing spreadsheet title to '{data_gs_title}'.") %>% message()
    app_lines[old_data_gs_title_line] <- sprintf("\tdata_gs_title = \"%s\",", data_gs_title)
    cat(app_lines, file = file.path(folder, "app.R"), sep = "\n")
    
    # update evaluation.Rmd
    if (file.exists(file.path(folder, "evaluation.Rmd"))) {
      readr::read_lines(file = file.path(folder, "evaluation.Rmd")) %>% 
        stringr::str_replace_all(
          "(data_gs_title ?= ?)\\\"([^\"]*)\\\"",
          sprintf("data_gs_title = \"%s\"", data_gs_title)) %>% 
      cat(file = file.path(folder, "evaluation.Rmd"), sep = "\n")
    }
    
  } else {
    # keeping old title
    data_gs_title <-
      app_lines[old_data_gs_title_line] %>% 
      stringr::str_match("data_gs_title ?= ?\\\"([^\"]*)\\\"") %>% 
      { .[,2] }
  }
  
  # check gs_access
  if (check_gs_access) {
    tbl_check_gs_access(folder = folder, data_gs_title = data_gs_title)
  }
  
  # finalize
  glue("Info: peer evaluation app from '{template}' is now fully duplicated in directory '{folder}'.",
       "Please modify the files in '{folder}' as appropriate and ",
       "run tbl_test_peer_evaluation('{folder}') before before uploading to shiny server.") %>% 
    message()
  
  return(invisible(folder))
}

#' Run a peer evaluation app
#'
#' This function starts the peer evaluation user interface. Note that this function is typically NOT called directly but indirectly by setting up the peer evalution app using \link{tbl_setup_peer_evaluation}, adjusting the files in the peer evaluation app folder, and test running the app using \link{tbl_test_peer_evaluation}.
#'
#' @inheritParams tbl_setup_peer_evaluation
#' @inheritParams peer_evaluation_server
#' @inheritParams peer_evaluation_ui
#' @param ... passed on to the \code{\link[shiny]{runApp}} call (only if \code{launch = TRUE}), can include server-specific parameters such as host or port
#' @param launch whether to launch the app (TRUE) or return a shiny app object (FALSE) that then can be launched via \code{\link[shiny]{runApp}}
#' @family peer evaluation functions
#' @export
tbl_run_peer_evaluation <- function(
  data_gs_title, 
  roster = read_excel("roster.xlsx"), 
  app_title = "Peer Evaluation", 
  welcome_md_file = "app_welcome.md", 
  self_eval_plus_md_file = "app_self_evaluation_plus.md", 
  self_eval_minus_md_file = "app_self_evaluation_minus.md", 
  teammate_eval_plus_md_file = "app_teammate_evaluation_plus.md", 
  teammate_eval_minus_md_file = "app_teammate_evaluation_minus.md", 
  quant_scores_md_file = "app_quantitative_scores.md",
  points_per_teammate = 10, max_points = 15, min_points = 0, min_point_difference = 2,
  require_self_eval = TRUE,
  require_peer_evals = TRUE,
  auto_login_access_code = NULL, ..., 
  launch = FALSE) {
  
  # require specific key file location for simplicity
  gs_key_file <- "gs_key_file.json"
  
  # safety checks
  if (!is.data.frame(roster)) stop("roster data frame required", call. = FALSE)
  content_files <- c(welcome_md_file, self_eval_plus_md_file, self_eval_minus_md_file, teammate_eval_plus_md_file, teammate_eval_minus_md_file, quant_scores_md_file)
  if (any(missing <- !file.exists(content_files)))
    glue("content files do not exist: '{glue::glue_collapse(content_files[missing], sep = \"', '\")}'") %>% 
    stop(call. = FALSE)
  if (!file.exists(gs_key_file)) glue("no key file found ('{gs_key_file}' is missing)") %>% stop(call. = FALSE)
  
  # start-up message
  glue(
    "\n***************************************************************",
    "\nInfo: launching Peer Evaluation GUI (version {packageVersion('tbltools')})...",
    "\nInfo: app title: '{app_title}'",
    "\nInfo: roster: {nrow(roster)} students in {length(unique(roster$team))} teams",
    "\nInfo: points per teammate: {points_per_teammate} ", 
    "(min: {min_points}, max: {max_points}, min diff: {min_point_difference})"
  ) %>% message()

  # generate app
  app <- shinyApp(
    ui = peer_evaluation_ui(app_title = app_title),
    server = peer_evaluation_server(
      roster = roster,
      data_gs_title = data_gs_title,
      gs_key_file = gs_key_file,
      welcome_md_file = welcome_md_file, 
      self_eval_plus_md_file = self_eval_plus_md_file, 
      self_eval_minus_md_file = self_eval_minus_md_file, 
      teammate_eval_plus_md_file = teammate_eval_plus_md_file, 
      teammate_eval_minus_md_file = teammate_eval_minus_md_file, 
      quant_scores_md_file = quant_scores_md_file,
      points_per_teammate = points_per_teammate,
      max_points = max_points,
      min_points = min_points,
      min_point_difference = min_point_difference,
      require_self_eval = require_self_eval,
      require_peer_evals = require_peer_evals,
      auto_login_access_code = auto_login_access_code
    )
  )
  
  # launch or return
  if (launch)
    runApp(app, display.mode = "normal", ...)
  else
    return(app)
}


#' Test run peer evaluation locally
#' 
#' This function starts a peer evaluation app previously set up using \link{tbl_setup_peer_evaluation}. This provides a local version of the app before deploying it to a shiny apps server (using \link{tbl_deploy_peer_evaluation}). Keep in mind that the test application writes data to the google spreadsheet and make sure to delete any test records from the google spreadsheet that may interfere with any students' peer evaluations prior to providing the students with the link to the deployed peer evaluation app. 
#' 
#' @param folder folder where the peer evaluation app is located (see \link{tbl_setup_peer_evaluation} for details)
#' @param ... optional parameters passed to \link[shiny]{runApp}
#' @family peer evaluation functions
#' @export
tbl_test_peer_evaluation <- function(folder = "peer_evaluation", ...) {
  check_peer_evaluation_folder(folder)
  runApp(folder, ...)
}

# convenience function for app existence check
check_peer_evaluation_folder <- function(folder) {
  if(!dir.exists(folder)) {
    glue("peer evaluation app folder '{folder}' does not exist") %>% 
      stop(call. = FALSE)
  }
  
  if (!file.exists(file.path(folder, "app.R"))) {
    glue("the folder '{folder}' does not seem to contain a peer evaluation app ('app.R' is missing)") %>% 
      stop(call. = FALSE)
  }
}

#' Deploy peer evaluation app
#' 
#' Upload the peer evaluation app to a shiny server via \link[rsconnect]{rsconnect}. This uses the rsconnect function \link[rsconnect]{deployApp} to upload or update a peer evaluation and thus requires rsconnect credentials to be already set. See \link[rsconnect]{setAccountInfo} or the \href{https://shiny.rstudio.com/articles/shinyapps.html#configure-rsconnect}{configuration help} for details on how to set your credentials for the \href{https://www.shinyapps.io}{shiny app platform}.
#' @param folder folder where the peer evaluation app is located (see \link{tbl_setup_peer_evaluation} for details)
#' @param appName name of the application for the web address on shiny.io. Can be provided manually but must be unique within an account. By default is guessed from the folder simply by removing special characters, making everything lower case, and replacing spaces with \code{_}.
#' @param ... additional optional parameters passed on to \link[rsconnect]{deployApp}
#' @family peer evaluation functionsde 
#' @export
tbl_deploy_peer_evaluation <- function(folder = "peer_evaluation", appName = guess_from(folder), ...) {
  
  if(!dir.exists(folder)) {
    glue("peer evaluation app folder '{folder}' does not exist") %>% 
      stop(call. = FALSE)
  }
  
  if (!file.exists(file.path(folder, "app.R"))) {
    glue("the folder '{folder}' does not seem to contain a peer evaluation app ('app.R' is missing)") %>% 
      stop(call. = FALSE)
  }
  
  # simplify app name
  guess_from <- function(x) {
    x %>% 
      stringr::str_to_lower() %>% 
      stringr::str_replace_all(fixed(" "), "_") %>% 
      stringr::str_remove_all("[$@#%!'\"&*(){}\\[\\]]")
  }
  
  tryCatch(
    deployApp(folder, appName = appName, ...),
    error = function(e) {
      glue("something went wrong trying to upload your peer evaluation app. ",
           "Please see the function help (?tbl_deploy_peer_evaluation) ", 
           "and make sure that your shiny server credentials are set properly. ",
           "The shiny apps server returned the following error: ", e$message) %>% 
        stop(call. = FALSE)
    }
  )
}

# peer evals data functions -----

#' Example files
#' @rdname tbl_example
#' @export
#' @details \code{tbl_example_peer_evaluation} returns the google spreadsheet key for an example peer evaluation dataset.
tbl_example_peer_evaluation <- function() {
  try_to_fetch_google_spreadsheet(gs_id = "1u9p0erH13N-KFGsAEEY5Eo2cyXJhR62SA485GaRP3O8")
}

#' @rdname tbl_example
#' @export
#' @details \code{tbl_example_empty_peer_evaluation} returns the google spreadsheet key for an example empty/newly set-up peer evaluation.
tbl_example_empty_peer_evaluation <- function() {
  try_to_fetch_google_spreadsheet(gs_id = "1WcxbU3NOIrOzhf-PAyNGlgpxiEPLMFthe-3lldoCc2M")
}

#' @rdname tbl_example
#' @export
#' @details \code{tbl_example_roster} returns the example roster data frame
tbl_example_roster <- function() {
  read_excel(system.file(package = "tbltools", "extdata", "roster_template.xlsx"))
}

#' Fetch the peer evaluation data
#' 
#' Fetches the peer evaluation data from the google spreadsheet and reads it (using \link{tbl_read_peer_evaluation_data}). For standard installations of the peer evaluation app, all defaults should be sufficient with only parameter \code{data_gs_title} requiring a specification.
#' @inheritParams tbl_setup_peer_evaluation
#' @inheritParams tbl_run_peer_evaluation
#' @param data_gs_id optional alternative to the \code{data_gs_title}, a google spread sheet ID text or object (see \link[googlesheets4]{sheets_id}). If provided, it takes precedence over the \code{data_gs_title} parameter as the google spreadsheet doesn't need to be searched by name anymore (i.e. can be loaded faster).
#' @param data_gs_key this parameter is no longer used (replaced by data_gs_id)
#' @param folder folder where the peer evaluation app is located (relative to the location of the RMarkdown file if used in the latter context)
#' @param download_to location where the whole peer evaluation data sheet will be downloaded to for more efficient read access
#' @export
tbl_fetch_peer_evaluation_data <- function(
  folder = ".", data_gs_title = NULL, data_gs_id = NULL, data_gs_key = deprecated(),
  roster = read_excel(file.path(folder, "roster.xlsx")), 
  gs_key_file = file.path(folder, "gs_key_file.json"),
  download_to = file.path(folder, "pe_data_downloaded.xlsx")) {
  
  # inform user about data_gs_key deprecation
  if (lifecycle::is_present(data_gs_key)) {
    lifecycle::deprecate_warn("0.6.0", "tbltools::tbl_fetch_peer_evaluation_data(data_gs_key = )", "tbltools::tbl_setup_peer_evaluation(data_gs_id = )")
    data_gs_id <- data_gs_key
  }
  
  # safety checks
  if (!is.data.frame(roster)) stop("roster data frame required", call. = FALSE)
  
  # google sheet
  if (is.null(data_gs_title) && is.null(data_gs_id))
    stop("a google spreadsheet must be identified either via data_gs_title or data_gs_id parameter, neither is provided", call. = FALSE)
  
  if (!is.null(data_gs_id) && is(data_gs_id, "sheets_id")) {
    message("Info: proceeding with provided google spreadsheet")
    gs <- data_gs_id
  } else {
    # authenticate and get gs via title
    gs <- tbl_check_gs_access(data_gs_title = data_gs_title, data_gs_id = data_gs_id, gs_key_file = gs_key_file)
  }
  
  # downloading data
  glue("Info: downloading data to '{download_to}'... ") %>% message(appendLF = FALSE)
  op <- options(googledrive_quiet = TRUE)
  on.exit(options(op))
  if(file.exists(download_to)) file.remove(download_to)
  result <- googledrive::drive_download(googledrive::as_id(gs), path = download_to)
  if(file.exists(download_to)) message("complete.") else message("failed.")
  
  # read data
  tbl_read_peer_evaluation_data(folder = folder, roster = roster, download_file = download_to)
}

#' Read downloaded peer evaluation data
#' 
#' Read peer evaluation data that's already downloaded. Usually called indirectly via \link{tbl_fetch_peer_evaluation_data} unless there is no reason to fetch the latest data from the google spreadsheet.
#' @inheritParams tbl_fetch_peer_evaluation_data
#' @param download_file downloaded peer evaluation data file, created by \link{tbl_fetch_peer_evaluation_data}
#' @export
tbl_read_peer_evaluation_data <- function(
  folder = ".", 
  roster = read_excel(file.path(folder, "roster.xlsx")),
  download_file = file.path(folder, "pe_data_downloaded.xlsx")) {
    
  # global vars
  team <- access_code <- timestamp <- submitted <- evaluatee_access_code <- submitted2 <- self_evaluation <- plus <- minus <- score <- NULL
  
  # safety checks
  if (!is.data.frame(roster)) stop("roster data frame required", call. = FALSE)
  students <- check_student_roster(roster) %>% 
    # get team member
    group_by(team) %>% 
    mutate(n_team_mates = dplyr::n() - 1L) %>% 
    ungroup() 
  
  # path
  if (!file.exists(download_file))
    glue("peer evaluation data file '{download_file}' does not exist, ",
         "make sure to run tbl_fetch_peer_evaluation_data() first ",
         "or adjust the 'download_file' parameter to point to a valid ",
         "peer evaluation data file") %>% 
    stop(call. = FALSE)
  
  # fetch student info
  access_code_prefix <- "id_"
  students <- students %>% mutate(access_code = str_c(access_code_prefix, access_code)) 
  pe_data <- students %>% 
    mutate(
      peer_eval = purrr::map(access_code, ~read_peer_eval(download_file, .x) %>% 
                               rename(evaluatee_access_code = access_code)),
      # safety check on timestamp column
      time_stamp_col = purrr::map_chr(peer_eval, ~class(.x$timestamp)[1])
    )
  
  if (any(problem <- pe_data$time_stamp_col != "POSIXct")) {
    glue::glue(
      "encountered problems with the timestamp column. Please check the ",
      "spreadsheet and make sure the 'timestamp' column on the following tabs ",
      "always has the same date & time format in each row. Problematic tabs:\n",
      "{paste(pe_data$access_code[problem], collapse = ', ')}"
    ) %>% stop(call. = FALSE)
  }
  
  # unnest the data (make sure those without records remain listed, hence the left join)
  pe_data <- 
    students %>% 
    dplyr::left_join(
      pe_data %>% select(access_code, peer_eval) %>% tidyr::unnest(peer_eval),
      by = "access_code"
    )
    
  # structure information and nest evaluations
  pe_data <- 
    pe_data %>% 
    mutate(
      started = !is.na(timestamp),
      submitted2 = ifelse(is.na(submitted), FALSE, submitted),
      submitted_timestamp = timestamp,
      self_evaluation = access_code == evaluatee_access_code
    ) %>% 
    # simplify column sorting
    select(-submitted, -timestamp) %>% rename(submitted = submitted2) %>% 
    # next data
    nest(evaluations = c(evaluatee_access_code, self_evaluation, plus, minus, score))
  
  # update timestamp (can't do inside mutate, problems with the NA)
  pe_data <- within(pe_data, submitted_timestamp[!submitted] <- NA)
  
  return(pe_data)
}

#' Summarize peer evaluation data
#' 
#' Summarizes the peer evaluation data. Preserves all roster information (last name, first name, team, + any custom fields).
#' 
#' @param data the peer evaluation data frame retrieved by \link{tbl_fetch_peer_evaluation_data}
#' @param submitted_only only include evaluations that were actually submitted (rather than just saved)
#' @export
tbl_summarize_peer_evaluation_data <- function(data, submitted_only = FALSE) {
  
  # global vars
  started <- submitted <- submitted_timestamp <- evaluations <- access_code <- evaluatee_access_code <- self_evaluation <- n_evaluations <- score <- plus <- minus <- NULL
  
  # safety
  if (missing(data) || !is.data.frame(data))
    stop("no data frame supplied")
  
  # check for required columns
  req_columns <- c("access_code", "evaluations")
  if (length(missing <- setdiff(req_columns, names(data))) > 0)
    glue("missing column(s) in data frame: {glue::glue_collapse(missing, sep=', ')}") %>% 
    stop(call. = FALSE)
  
  summarize_evals <- . %>% sample() %>% stats::na.omit() %>% glue::glue_collapse(sep = "\n\n") %>% { ifelse(is.null(.), NA_character_, .) }
  
  # make sure to preserve custom roster info
  roster <- data %>% select(-started, -submitted, -submitted_timestamp, -evaluations) %>% 
    select(evaluatee_access_code = access_code, everything())
  
  # summarize information
  data_sum <- data %>% 
    select(access_code, submitted, evaluations) %>%
    unnest(evaluations) %>% 
    filter(submitted | !submitted_only) %>% 
    select(-access_code, -submitted) %>% 
    group_by(evaluatee_access_code) %>%
    summarize(
      n_evaluations = sum(!self_evaluation, na.rm = TRUE),
      score_avg = ifelse(n_evaluations > 0, mean(score[!self_evaluation]), NA_real_),
      self_plus = plus[self_evaluation] %>% summarize_evals,
      self_minus = minus[self_evaluation] %>% summarize_evals,
      team_plus = plus[!self_evaluation] %>% summarize_evals,
      team_minus = minus[!self_evaluation] %>% summarize_evals
    ) 
  
  # return
  left_join(roster, data_sum, by = "evaluatee_access_code") %>% 
    mutate(n_evaluations = ifelse(is.na(n_evaluations), 0, n_evaluations))
}

#' Export peer evaluation data
#' 
#' Exports peer evaluation data - both raw data and data summary (see \link{tbl_summarize_peer_evaluation_data} for details).
#' 
#' @inheritParams tbl_summarize_peer_evaluation_data
#' @param filepath the excel file where to save the peer evaluation data summary
#' @param ... parameters passed on to \code{\link{tbl_summarize_peer_evaluation_data}}
#' @return returns the passed in data invisibly to permit use of this function inside pipelines
#' @export
tbl_export_peer_evaluation_data <- function(data, filepath = "pe_data_summary.xlsx", ...) {
  
  # global vars
  evaluations <- NULL
  
  # safety
  if (missing(data) || !is.data.frame(data))
    stop("no data frame supplied")
  
  glue("Info: exporting peer evaluation data and data summary to '{filepath}'... ") %>% 
    message(appendLF = FALSE)
  
  # cell and header styles
  style <- createStyle(valign = "top", wrapText = TRUE)
  header_style <- createStyle(textDecoration = "bold", border="bottom", borderColour = "#000000", borderStyle = "medium")
  
  # data
  data_all <- data %>% unnest(evaluations)
  data_sum <- data %>% tbl_summarize_peer_evaluation_data(...)
  
  # work book
  wb <- createWorkbook()
  
  # summary work sheet
  ws <- addWorksheet(wb, "summary")
  writeData(wb, ws, data_sum, headerStyle = header_style)
  freezePane(wb, ws, firstRow = TRUE)
  setColWidths(wb, ws, cols = 1:ncol(data_sum), widths = "auto")
  addStyle(wb, ws, style, rows = 1:(nrow(data_sum) + 1), cols = 1:ncol(data_sum), gridExpand = TRUE, stack = TRUE)
  
  # data work sheet
  ws <- addWorksheet(wb, "data")  
  writeData(wb, ws, data_all, headerStyle = header_style)
  freezePane(wb, ws, firstRow = TRUE)
  setColWidths(wb, ws, cols = 1:ncol(data_all), widths = "auto")
  addStyle(wb, ws, style, rows = 1:(nrow(data_all) + 1), cols = 1:ncol(data_all), gridExpand = TRUE, stack = TRUE)
  
  # save data sheet
  saveWorkbook(wb, filepath, overwrite = TRUE)
  
  message("completed.")
  
  return(invisible(data))
}

# utility functions ====

#' Generate random access codes
#' 
#' Utility function to generate a list of random access codes that can be copied into an Excel column.
#' @param n how many access codes to generate
#' @param length how many characters for each acccess code
#' @return returns the access codes invisible
#' @export
tbl_generate_access_codes <- function(n, length = 4) {
  codes <- sapply(1:n, function(i) {
    sample(1:36, length, replace = TRUE) %>% 
      sapply(function(x) if (x>26) x-27 else LETTERS[x]) %>% 
      paste(collapse = "")
  }) 
  codes %>% cat(sep = "\n")
  return(invisible(codes))
}

# check functions =====

# safety checks for student roster data frame
check_student_roster <- function(roster) {
  
  # global vars:
  access_code <- n <- NULL
  
  # check for data frame
  if(!is.data.frame(roster))
    stop("student roster must be a data frame", call. = FALSE)
  
  # check for required columns
  req_columns <- c("last", "first", "access_code", "team")
  if (length(missing <- setdiff(req_columns, names(roster))) > 0)
    glue("missing column(s) in student roster: {glue::glue_collapse(missing, sep=', ')}") %>% 
    stop(call. = FALSE)
  
  # check for unique access codes
  not_unique <- roster %>% group_by(access_code) %>% tally() %>% filter(n > 1)
  if (nrow(not_unique) > 0) {
    glue("all access codes must be unique, found not unique access code(s): ",
         "{glue::glue_collapse(not_unique$access_code, sep = ', ')}") %>% 
      stop(call. = FALSE)
  }
  
  return(mutate(roster, access_code = as.character(access_code)))
}

# authentication =======

#' Check google spreadsheet access
#' 
#' This function checks whether google spreadsheet credentials are established and there is access to the \code{data_gs_title} google sheet. The  \code{gs_key_file} must grant access to the google spreadsheet (\code{data_gs_title}). See the \href{https://tbltools.kopflab.org/articles/peer_evaluations.html}{peer evaluations vignette} for details on how to set up google credentials and generate a key file.
#' 
#' @inheritParams tbl_setup_peer_evaluation
#' @inheritParams tbl_fetch_peer_evaluation_data
#' @return returns the retrieved authentication token from the key file invisibly
#' @family peer evaluation functions
#' @export
tbl_check_gs_access <- function(folder = "peer_evaluation", data_gs_title = "Peer Evaluation", data_gs_id = NULL, gs_key_file = file.path(folder, "gs_key_file.json")) {
  
  # authentication check
  glue("Info: testing authentication with key file '{gs_key_file}'... ") %>% message()
  try_to_authenticate(gs_key_file)
  message("Info: authentication successful.")
  
  # fetch google spreadsheet
  op <- options(googledrive_quiet = TRUE)
  on.exit(options(op))
  if (!is.null(data_gs_id)) {
    glue("Info: looking for spreadsheet '{data_gs_id}'... ") %>% message()
    gs <- try_to_fetch_google_spreadsheet(gs_id = data_gs_id)
  } else if (!is.null(data_gs_title)) {
    glue("Info: looking for spreadsheet '{data_gs_title}'... ") %>% message()
    gs <- try_to_fetch_google_spreadsheet(gs_title = data_gs_title)
  }
  message("Info: spreadsheet retrieved successfully.")
  
  return(invisible(gs))
}

# authenticate with google server using the key file
# @return the authentication token if successful
try_to_authenticate <- function(gs_key_file) {
  
  # google sheets authentication
  googlesheets4::gs4_deauth()
  googledrive::drive_deauth()
  
  # check that the file exists
  if (!file.exists(gs_key_file))
    glue("key file does not exist, make sure there is a valid key file at '{gs_key_file}'.") %>% 
    stop(call. = FALSE)
  
  # authenticate with key file
  tryCatch(
    token_obj <- gargle::credentials_service_account(
      path = gs_key_file,
      scopes = c(
        "https://www.googleapis.com/auth/spreadsheets", # full access to sheets
        "https://www.googleapis.com/auth/drive.readonly" # read only access to drive files
      )
    ),
    error = function(e) {
      glue("google authentication failed: {e$message}. Please try again.") %>% 
        stop(call. = FALSE)
    }
  )
  
  # check token
  if (is.null(token_obj))
    stop("google authentication failed with the provided key file", call. = FALSE)
  
  # run authentication (this should always work at this point but if not, might run into trouble with this asking users to authenticate differently)
  googlesheets4::gs4_auth(token = token_obj)
  googledrive::drive_auth(token = token_obj)

  # check result
  if (
    !(googlesheets4::gs4_has_token() && identical(googlesheets4::gs4_token()$auth_token$hash(), token_obj$hash())) ||
    !(googledrive::drive_has_token() && identical(googledrive::drive_token()$auth_token$hash(), token_obj$hash()))
  )  {
    stop("google authentication failed with the provided key file", call. = FALSE)
  }
  
  # return token
  return(token_obj)
}

# find google spreadsheet by title or id
# @return the google spreadsheet if successful
try_to_fetch_google_spreadsheet <- function(gs_title, gs_id) {
  
  if (!missing(gs_id)) {
    tryCatch(
      gs <- googlesheets4::as_sheets_id(gs_id),
      error = function(e) {
        glue("could not retrieve google spreadsheet with id {gs_id} - ",
             "encountered the following error: {e$message}") %>% 
          stop(call. = FALSE)
      }
    )
    return(gs)
  } else if (!missing(gs_title)) {
    tryCatch(
      gs <- googledrive::drive_get(gs_title),
      error = function(e) {
        glue("could not retrieve google spreadsheet with title '{gs_title}' - ",
             "encountered the following error: {e$message}") %>% 
          stop(call. = FALSE)
      }
    )
    # checks
    if (nrow(gs) == 1L) {
      return(googlesheets4::as_sheets_id(gs))
    } else if (nrow(gs) == 0L) {
      stop("don't have access to a unique sheet with this exact name", call. = FALSE) 
    } else {
      stop("multiple sheets with this name exist, not sure what to do", call. = FALSE)
    }
  }
  stop("neither gs_id nor gs_title provided", call. = FALSE)
}

# data loading/saving functions ==========

# load peer evaluation
# @param ss - spreadsheet
read_peer_eval <- function(ss, access_code) {
  
  # global vars
  timestamp <- score <- NULL
  
  is_gs <- is(ss, "sheets_id")
  
  if (is_gs) {
    # refresh sheet
    gs <- googlesheets4::as_sheets_id(ss)
    worksheets <- googlesheets4::sheet_names(gs)
  } else {
    # make sure file exists
    if (!file.exists(ss)) 
      glue("provided spreadsheet is neither a google spreadsheet nor a valid path to a local excel file") %>% 
      stop(call. = FALSE)
    worksheets <- excel_sheets(ss)
  }
  
  # check if tab exists
  if (!access_code %in% worksheets) {
    # does not exist
    return(
      tibble(
        timestamp = now(),
        submitted = logical(0),
        access_code = character(0),
        plus = character(0),
        minus = character(0),
        score = integer(0)
      )
    )
  } else if (is_gs) {
    # does exist and is a google spreadsheet
    data <- gs %>% 
      # retrieve data
      googlesheets4::read_sheet(
        sheet = access_code, 
        col_types = "c"
      ) %>% 
      # process columns
      dplyr::transmute(
        timestamp = ymd_hms(timestamp),
        submitted = readr::parse_logical(submitted),
        access_code = access_code,
        plus = plus,
        minus = minus,
        score = readr::parse_integer(score)
      ) 
  } else {
    # does exist and is a local file
    data <- read_excel(ss, sheet = access_code) %>% 
      mutate(
        plus = as.character(plus),
        minus = as.character(minus)
      )
  }
  
  # return
  data %>% 
    # make sure score is numeric
    mutate(score = quietly(as.numeric)(score)$result) %>% 
    # filter only most recent entry
    filter(timestamp == max(timestamp)) %>% 
    return()
}

# save peer evaluation
save_peer_eval <- function(gs, access_code, data, submitted = FALSE) {
  
  # global vars
  timestamp <- NULL
  
  # refresh sheet
  gs <- googlesheets4::as_sheets_id(gs)
  
  # add timestamp and submitted info
  data <- data %>% 
    mutate(
      timestamp = now("UTC"),
      submitted = submitted
    ) %>% 
    select(timestamp, submitted, everything()) %>% 
    as.data.frame()
  
  # check for spreadsheet
  if (!access_code %in% googlesheets4::sheet_names(gs)) {
    glue("Info: creating {nrow(data)} rows in new gs tab '{access_code}'") %>% message()
    googlesheets4::sheet_write(data = data, ss = gs, sheet = access_code)
  } else {
    # add new rows
    glue("Info: adding {nrow(data)} rows to tab '{access_code}'") %>% message()
    googlesheets4::sheet_append(ss = gs, data = data, sheet = access_code)
  }
  
}