R/add_server.R

In teachingApps: Apps for Teaching Statistics, R Programming, and Shiny App Development

#' Add the server of one app to the server of another app
#'
#' @description Sources a \code{server.R} file before parsing and evaluating its contents in a specified environment
#'
#' @param app  Name of the teachingApp from which the content of the \code{server.R} will be pulled
#' @param path Path to a directory containing the app from which the content of the \code{server.R} will be pulled
#' @param env  Environment in which the call is made, typically \code{environment()}
#'
#' @importFrom shiny addResourcePath
#'
#' @details Currently, this function can be used to insert an \code{server} into
#'          a \code{navbarPage} app.  The types of apps that can be inserted are:
#'          
#'      \itemize{
#'          \item{\code{fluidPage}}{}
#'          \item{\code{bootstrapPage}}{}
#'          \item{\code{pageWithSidebar}}{}
#'          \item{\code{basicPage}}{}
#'          \item{\code{fixedPage}}{}
#'       }          
#'          A \code{server} can be added as an entire \code{tabPanel} or as a row within 
#'          within a \code{tabPanel} portion of a shiny app. 
#'          
#'          May be used with apps stored in packages other than teachingApps.  
#'          However, apps are assumed be stored in the \code{apps/} directory located 
#'          at top level of the package.
#'  
#' @return An \code{Observer}-class object resulting from evaluating a \code{server.R} file
#' @seealso \code{\link{add_ui}},  \code{\link{add_rmd}}
#' @examples \dontrun{
#' 
#' ## server.R from app: 'maximum_likelihood'
#' 
#' server_ml <- system.file('apps', 
#'                          'maximum_likelihood',
#'                          'server.R',
#'                          package = 'teachingApps') 
#' browseURL(server_ml)
#' 
#' ## server.R from app: 'distribution_weibull'
#' 
#' server_dw <- system.file('apps', 
#'                          'distribution_weibull',
#'                          'server.R',
#'                          package = 'teachingApps') 
#' browseURL(server_dw)
#' 
#' }
#' @export
add_server <- function(app, path, env = NULL) {
  
  no_app  <- missing(app)  || is.null(app)  || is.na(app)
  no_path <- missing(path) || is.null(path) || is.na(path)
  
  if( no_app &&  no_path) stop('Either an app or a path must be specified')
  if(!no_app && !no_path) stop('Only one app or path should be specified')

  if(no_path) {
    
     file <- system.file('apps', app, 'server.R', package = 'teachingApps')
      
    } else {
    
     shiny::addResourcePath(basename(path), path)
     file <- file.path(path, 'server.R')
    
    }
       
  serve <- source(file = file)
  texts <- parse(text = body(serve[[1]])[-1])
  
  eval(texts, envir = env)
  
}