(*****************************************************************************

  Liquidsoap, a programmable audio stream generator.
  Copyright 2003-2023 Savonet team

  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details, fully stated in the COPYING
  file at the root of the liquidsoap distribution.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA

 *****************************************************************************)

open Source
open Extralib

module List = struct
  include List

  let mean l = List.fold_left ( +. ) 0. l /. float_of_int (List.length l)
end

(** Second order IIR filter. *)
module IIR = struct
  type sample = float array

  type t = {
    channels : int;
    mutable x : sample * sample;
    (* (x', x'') *)
    mutable y : sample * sample;
    (* (y', y'') *)
    a1 : float;
    a2 : float;
    b0 : float;
    b1 : float;
    b2 : float;
  }

  (** Create and IIR filter. The coefficients are given for a samplerate of 48
      kHz and are adjusted for required target samplerate. *)
  let create ~channels ~samplerate ~a1 ~a2 ~b0 ~b1 ~b2 =
    let blank = Array.make channels 0. in
    let x = (blank, blank) in
    let y = (blank, blank) in
    if samplerate = 48000. then { channels; x; y; a1; a2; b0; b1; b2 }
    else (
      (* The coefficients of the specification are given for a 48 kHz samplerate,
         this computes the values for other samplerates. This is "strongly
         inspired" of https://github.com/klangfreund/LUFSMeter/ *)
      let k_q = (2. -. (2. *. a2)) /. (a2 -. a1 +. 1.) in
      let k = sqrt ((a1 +. a2 +. 1.) /. (a2 -. a1 +. 1.)) in
      let q = k /. k_q in
      let atan_k = atan k in
      let vb = (b0 -. b2) /. (1. -. a2) in
      let vh = (b0 -. b1 +. b2) /. (a2 -. a1 +. 1.) in
      let vl = (b0 +. b1 +. b2) /. (a1 +. a2 +. 1.) in
      let k = tan (atan_k *. 48000. /. samplerate) in
      let a = 1. /. (1. +. (k /. q) +. (k *. k)) in
      let b0 = (vh +. (vb *. k /. q) +. (vl *. k *. k)) *. a in
      let b1 = 2. *. ((vl *. k *. k) -. vh) *. a in
      let b2 = (vh -. (vb *. k /. q) +. (vl *. k *. k)) *. a in
      let a1 = 2. *. ((k *. k) -. 1.) *. a in
      let a2 = (1. -. (k /. q) +. (k *. k)) *. a in
      { channels; x; y; a1; a2; b0; b1; b2 })

  let stage1 =
    create ~a1:(-1.69065929318241) ~a2:0.73248077421585 ~b0:1.53512485958697
      ~b1:(-2.69169618940638) ~b2:1.19839281085285

  let stage2 =
    create ~a1:(-1.99004745483398) ~a2:0.99007225036621 ~b0:1. ~b1:(-2.) ~b2:1.

  (** Process a sample. *)
  let process iir x =
    let channels = iir.channels in
    assert (Array.length x = channels);
    let x', x'' = iir.x in
    let y', y'' = iir.y in
    let y = Array.make channels 0. in
    for i = 0 to channels - 1 do
      y.(i) <-
        (iir.b0 *. x.(i))
        +. (iir.b1 *. x'.(i))
        +. (iir.b2 *. x''.(i))
        -. (iir.a1 *. y'.(i))
        -. (iir.a2 *. y''.(i))
    done;
    iir.x <- (x, x');
    iir.y <- (y, y');
    y
end

(** Compute the loudness from the mean of squares. *)
let loudness z = -0.691 +. (10. *. log10 z)

class lufs window source =
  object (self)
    inherit operator [source] ~name:"lufs" as super
    method stype = source#stype
    method private _is_ready = source#is_ready
    method remaining = source#remaining
    method seek_source = source#seek_source
    method abort_track = source#abort_track
    method self_sync = source#self_sync
    method channels = self#audio_channels
    method samplerate = float_of_int (Lazy.force Frame.audio_rate)
    val mutable stage1 = id
    val mutable stage2 = id

    (** Current mean square (weighted sum over channels). *)
    val mutable ms = 0.

    (** Length of current mean square in samples *)
    val mutable ms_len = 0

    (** Last 100ms blocks. *)
    val mutable ms_blocks = []

    method! wake_up a =
      super#wake_up a;
      let channels = self#channels in
      let samplerate = self#samplerate in
      stage1 <- IIR.process (IIR.stage1 ~channels ~samplerate);
      stage2 <- IIR.process (IIR.stage2 ~channels ~samplerate)

    (** Compute LUFS. *)
    method compute =
      (* Compute ms of overlapping 400ms blocks. *)
      let blocks =
        let rec aux b' b'' b''' = function
          | b :: l -> ((b +. b' +. b'' +. b''') /. 4.) :: aux b b' b'' l
          | [] -> []
        in
        let aux = function b :: b' :: b'' :: l -> aux b b' b'' l | _ -> [] in
        aux ms_blocks
      in
      (* Blocks over absolute threshold. *)
      let absolute = List.filter (fun z -> loudness z > -70.) blocks in
      (* Relative threshold. *)
      let threshold = loudness (List.mean absolute) -. 10. in
      (* Blocks over relative threshold. *)
      let relative = List.filter (fun z -> loudness z > threshold) blocks in
      (* Compute LUFS. *)
      loudness (List.mean relative)

    (** Momentary LUFS. *)
    method momentary = loudness (List.mean (List.prefix 4 ms_blocks))

    method private get_frame buf =
      let channels = self#channels in
      let len_100ms = Frame.audio_of_seconds 0.1 in
      let offset = AFrame.position buf in
      source#get buf;
      let position = AFrame.position buf in
      let buf = AFrame.pcm buf in
      for i = offset to position - 1 do
        let x = Array.init channels (fun c -> buf.(c).(i)) in
        (* Prefilter. *)
        let x = stage1 x in
        let x = stage2 x in
        (* Add squares. *)
        for c = 0 to channels - 1 do
          let xc = x.(c) in
          ms <- ms +. (xc *. xc)
        done;
        ms_len <- ms_len + 1;
        (* When we have 100ms of squares we push the block. *)
        if ms_len >= len_100ms then (
          ms_blocks <- (ms /. float_of_int len_100ms) :: ms_blocks;
          ms <- 0.;
          ms_len <- 0)
      done;
      (* Keep only a limited (by the window) number of blocks. *)
      ms_blocks <- List.prefix (int_of_float (window () /. 0.1)) ms_blocks
  end

let _ =
  let return_t =
    Lang.frame_t (Lang.univ_t ())
      (Frame.Fields.make ~audio:(Format_type.audio ()) ())
  in
  Lang.add_operator "lufs" ~category:`Visualization
    ~meth:
      [
        ( "lufs",
          ([], Lang.fun_t [] Lang.float_t),
          "Current value for the LUFS (short-term value computed over the \
           duration specified by the `window` parameter).",
          fun s -> Lang.val_fun [] (fun _ -> Lang.float s#compute) );
        ( "lufs_momentary",
          ([], Lang.fun_t [] Lang.float_t),
          "Momentary LUFS (over a 400ms window).",
          fun s -> Lang.val_fun [] (fun _ -> Lang.float s#momentary) );
      ]
    ~return_t
    ~descr:
      "Compute current LUFS of the source according to the EBU R128 standard. \
       It returns the source with a method to compute the current value."
    [
      ( "window",
        Lang.getter_t Lang.float_t,
        Some (Lang.float 3.),
        Some "Duration of the window (in seconds) used to compute the LUFS." );
      ("", Lang.source_t return_t, None, None);
    ]
    (fun p ->
      let f v = List.assoc v p in
      let src = Lang.to_source (f "") in
      let window = Lang.to_float_getter (f "window") in
      new lufs window src)
