(** Expose metrics over HTTP in the prometheus format *)

type tags = (string * string) list

(** Registry for metrics. *)
module Registry : sig
  type t
  (** The registry contains a group of metrics *)

  val create : unit -> t

  val emit : Buffer.t -> t -> unit
  (** Write metrics into the given buffer. The buffer will be
      cleared first thing. *)

  val emit_str : t -> string
end

val global : Registry.t

(** Counters *)
module Counter : sig
  type t
  (** A counter, monotonically increasing *)

  val create : Registry.t -> ?tags:tags -> ?descr:string -> string -> t
  val inc : t -> unit
  val inc_by : t -> int -> unit
  val dec : t -> unit
  val dec_by : t -> int -> unit
end

(** Gauges *)
module Gauge : sig
  type t
  (** A gauge, taking arbitrary values *)

  val create : Registry.t -> ?tags:tags -> ?descr:string -> string -> t
  val set : t -> int -> unit
  val inc : t -> unit
  val inc_by : t -> int -> unit
  val dec : t -> unit
  val dec_by : t -> int -> unit
end

(* TODO:
   module Histogram : sig
   end
*)