#' saveRDS for lgb.Booster models
#'
#' Attemps to save a model using RDS. Has an additional parameter (\code{raw}) which decides whether to save the raw model or not.
#' 
#' @param object R object to serialize.
#' @param file a connection or the name of the file where the R object is saved to or read from.
#' @param ascii a logical. If TRUE or NA, an ASCII representation is written; otherwise (default), a binary one is used. See the comments in the help for save.
#' @param version the workspace format version to use. \code{NULL} specifies the current default version (2). Versions prior to 2 are not supported, so this will only be relevant when there are later versions.
#' @param compress a logical specifying whether saving to a named file is to use "gzip" compression, or one of \code{"gzip"}, \code{"bzip2"} or \code{"xz"} to indicate the type of compression to be used. Ignored if file is a connection.
#' @param refhook a hook function for handling reference objects.
#' @param raw whether to save the model in a raw variable or not, recommended to leave it to \code{TRUE}.
#' 
#' @return NULL invisibly.
#' 
#' @examples
#' \dontrun{
#'   library(lightgbm)
#'   data(agaricus.train, package = "lightgbm")
#'   train <- agaricus.train
#'   dtrain <- lgb.Dataset(train$data, label = train$label)
#'   data(agaricus.test, package = "lightgbm")
#'   test <- agaricus.test
#'   dtest <- lgb.Dataset.create.valid(dtrain, test$data, label = test$label)
#'   params <- list(objective = "regression", metric = "l2")
#'   valids <- list(test = dtest)
#'   model <- lgb.train(params,
#'                      dtrain,
#'                      100,
#'                      valids,
#'                      min_data = 1,
#'                      learning_rate = 1,
#'                      early_stopping_rounds = 10)
#'   saveRDS.lgb.Booster(model, "model.rds")
#' }
#' 
#' @export
saveRDS.lgb.Booster <- function(object,
                                file = "",
                                ascii = FALSE,
                                version = NULL,
                                compress = TRUE,
                                refhook = NULL,
                                raw = TRUE) {
  
  # Check if object has a raw value (and if the user wants to store the raw)
  if (is.na(object$raw) & (raw)) {
    
    # Save model
    object$save()
    
    # Save RDS
    saveRDS(object,
            file = file,
            ascii = ascii,
            version = version,
            compress = compress,
            refhook = refhook)
    
    # Free model from memory
    object$raw <- NA
    
  } else {
    
    # Save as usual
    saveRDS(object,
            file = file,
            ascii = ascii,
            version = version,
            compress = compress,
            refhook = refhook)
    
  }
  
}
