Remove switch operator, implement simple fallback core operator, use …

…cross to define top-level fallback operator, define switch using it.

src/core/dune

@@ -95,6 +95,7 @@
   external_input_audio
   external_input_video
   extralib
+  fallback
   fdkaac_format
   ffmpeg_format
   file_watcher
@@ -220,7 +221,6 @@
   stringView
   strings
   swap
-  switch
   synth_op
   synthesized
   term

src/core/operators/fallback.ml

@@ -0,0 +1,88 @@
+(*****************************************************************************
+
+  Liquidsoap, a programmable audio stream generator.
+  Copyright 2003-2022 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
+
+ *****************************************************************************)
+
+class fallback ~track_sensitive sources =
+  let self_sync_type = Utils.self_sync_type sources in
+  object (self)
+    inherit Source.operator ~name:"fallback" sources
+    val mutable selected = None
+    method selected = selected
+
+    method stype =
+      if List.exists (fun s -> s#stype = `Infallible) sources then `Infallible
+      else `Fallible
+
+    method self_sync =
+      ( Lazy.force self_sync_type,
+        match selected with Some s -> snd s#self_sync | None -> false )
+
+    method remaining =
+      match selected with Some s when track_sensitive -> s#remaining | _ -> -1
+
+    method seek n = match selected with Some s -> s#seek n | None -> 0
+    method is_ready = List.exists (fun s -> s#is_ready) sources
+
+    method private get_frame buf =
+      (* This is guanranteed to succeed because if #is_ready above *)
+      let s =
+        match selected with
+          | Some s when track_sensitive && s#is_ready -> s
+          | _ ->
+              let s = List.find (fun s -> s#is_ready) sources in
+              self#log#info "selected %s" s#id;
+              selected <- Some s;
+              s
+      in
+      s#get buf
+
+    method abort_track =
+      match selected with Some s -> s#abort_track | None -> ()
+  end
+
+let () =
+  let kind = Lang.any in
+  let return_t = Lang.frame_kind_t kind in
+  Lang.add_operator "fallback" ~return_t
+    ~meth:
+      [
+        ( "selected",
+          ([], Lang.fun_t [] (Lang.nullable_t (Lang.source_t return_t))),
+          "Currently selected source.",
+          fun s ->
+            Lang.val_fun [] (fun _ ->
+                match s#selected with
+                  | Some s -> Lang.source s
+                  | None -> Lang.null) );
+      ]
+    ~category:`Track
+    ~descr:"Select source to play based on first source available."
+    [
+      ( "track_sensitive",
+        Lang.bool_t,
+        Some (Lang.bool false),
+        Some "Re-select only on end of tracks." );
+      ("", Lang.list_t (Lang.source_t return_t), None, None);
+    ]
+    (fun p ->
+      let track_sensitive = Lang.to_bool (List.assoc "track_sensitive" p) in
+      let sources = List.map Lang.to_source (Lang.to_list (List.assoc "" p)) in
+      new fallback ~track_sensitive sources)