R/capin_metadata.R

In sckott/capins: Content Addressable Pins

#' file metadata
#' 
#' associate metadata with a file
#' @export
#' @param x (character) a file path
#' @param metadata metadata something or other
#' @return file path for the metadata file, containing
#' RDF
#' @examples
#' library(contentid)
#' f <- system.file("extdata", "vostok.icecore.co2", package = "contentid")
#' x <- capin(f)
#' 
#' # create some metadata file
#' library(rdflib)
#' r <- rdf()
#' rdf_add(r,
#'   subject = "http://www.dajobe.org/",
#'   predicate = "http://purl.org/dc/elements/1.1/language",
#'   object = "en")
#' rdf_add(r,
#'   subject = "b0",
#'   predicate = "http://purl.org/dc/elements/1.1/title",
#'   object = "Dave Beckett's Home Page")
#' rdf_add(r,
#'   subject = "b0",
#'   predicate = "http://purl.org/dc/elements/1.1/title",
#'   object = "Dave Beckett's Home Page")
#' rdf_add(r,
#'   subject = "b0",
#'   predicate = "http://purl.org/dc/elements/1.1/creator",
#'   object = "Dave Beckett")
#' # write metadata to a file
#' mfile <- capin_metadata(x, metadata=r)
#' # read back the metadata file
#' rdflib::rdf_parse(mfile)
capin_metadata <- function(metadata, x) {
  UseMethod("capin_metadata")
}

#' @export
capin_metadata.rdf <- function(metadata, x) {
  if (!contentid:::is_hash(x, "hashuri"))
    stop("'x' should be a contentid hash")
  hex <- last(stract(x, contentid:::hex_regex)[[1]])
  file <- paste0(hex, ".rdf")
  rdflib::rdf_serialize(metadata, file)
  return(file)
}

#' @export
capin_metadata.default <- function(metadata, x) {
  stop("no 'capin_metadata' method for ", class(metadata)[[1L]])
}