let predicate fn opt = Option.(to_list @@ map fn opt)

let authored query_string =
  let q = Person.Set.of_query @@ String_set.query query_string in
  fun n -> Person.Set.predicate q n.Text.authors

let ided query_string =
	let len = String.length query_string in
	fun n ->
		try String.sub n.Text.id 0 len = query_string
		with Invalid_argument _ -> false

let keyworded query_string =
  let q = String_set.query query_string in
  fun n -> String_set.(predicate q (Text.set "Keywords" n))

let topics query_string =
  let q = String_set.query query_string in
  fun n -> String_set.(predicate q (Text.set "Topics" n))

let apply_sys_util env def_env r order_opt reverse_opt number_opt authors_opt topics_opt id_opt =
	let predicates = if id_opt <> "" then [ ided id_opt ] else []
		@ predicate authored authors_opt
		@ predicate topics topics_opt in
	let predicate text = List.fold_left (fun a e -> a && e text) true predicates in
	let util = try Sys.getenv env with Not_found -> def_env in
	let print_text acc (_t, fnames) = Printf.sprintf "%s %s" acc (List.hd fnames) in
	let paths = match order_opt with
	| false -> File_store.fold ~r ~predicate print_text ""
	| true ->
		let order = match reverse_opt with true -> File_store.newest | false -> File_store.oldest in
		match number_opt with
		| Some number -> File_store.fold ~r ~predicate ~order ~number print_text ""
		| None -> File_store.fold ~r ~predicate ~order print_text ""
	in if paths = "" then ()
	else (ignore @@ Sys.command @@ Printf.sprintf "%s %s" util paths)