(* TODO Taler documentation
   markdown mimetype should be the prefered one, and be supported, according to DD
   we take text/plain as default instead for now *)
let default_extension = "txt"

let is_valid_filename, media_to_extension =
  let mimetype_ext_assoc =
    [
      (("text", "plain"), "txt"); (("text", "markdown"), "md")
    ; (("text", "html"), "html"); (("text", "html"), "htm")
    ; (("application", "pdf"), "pdf"); (("image", "jpeg"), "jpg")
    ; (("image", "jpeg"), "jpeg"); (("image", "png"), "png")
    ; (("image", "gif"), "gif")
    ]
  in
  (* <> than the actual set of "supported" extension (which depends on config files) *)
  let all_known_extensions = mimetype_ext_assoc |> List.split |> snd in
  let is_valid_filename path = Fpath.mem_ext all_known_extensions path in
  let media_to_extension = function
    | Cohttp.Accept.MediaType (m, m_sub) ->
        List.assoc_opt (m, m_sub) mimetype_ext_assoc
    | AnyMediaSubtype m ->
        List.find_map
          (fun ((m', _), ext) ->
            match String.equal m m' with false -> None | true -> Some ext)
          mimetype_ext_assoc
    | AnyMedia -> Some default_extension
  in
  (is_valid_filename, media_to_extension)