extract parameters from roxygen metadata tag

get_params.R

#' extract parameters from roxygen tags
#'
#' extract parameters from roxygen tags
#'
#' @param n Namespace
#' @param f Function
#'
#' @importFrom tools Rd_db
#' @importFrom jsonlite fromJSON
#'
#' @export
#'
get_params <- function(n, f) {
  db <- tools::Rd_db(n)
  fn_rd <- db[[paste0(f, ".Rd")]]
  
  ## get list of attributes
  fn_attributes <- lapply(fn_rd, attributes)
  
  ## get sections
  fn_sections <- which(
    sapply(fn_attributes, function(x) {
      x$Rd_tag == "\\section"
    })
  )
  
  ## get param section
  fn_params <- which(
    sapply(fn_rd[fn_sections], function(x) {
      x[[1]] == "Metadata"
    })
  )
  
  if (length(fn_params) > 0) {
    
    input_tags <- fn_rd[[fn_sections[fn_params]]]
    param_tag <- input_tags[[2]][[2]]
    return(jsonlite::fromJSON(as.character(param_tag), simplifyVector = FALSE))
    
  } else {
    
    return(NULL)
    
  }
  
}