youtube.lua: update "n" descrambling function name parsing

The descrambling function is now called through an intermediate array
variable. This change has also added two extra ways to recover the
function name. Add support to parse and resolve any of them.

Fixes #26574

share/lua/playlist/youtube.lua

@@ -1,7 +1,7 @@
 --[[
  $Id$
 
- Copyright © 2007-2021 the VideoLAN team
+ Copyright © 2007-2022 the VideoLAN 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
@@ -119,8 +119,37 @@ function n_descramble( nparam, js )
     end
 
     -- Look for the descrambler function's name
-    -- a.D&&(b=a.get("n"))&&(b=lha(b),a.set("n",b))}};
-    local descrambler = js_extract( js, '[=%(,&|](...?)%(.%),.%.set%("n",' )
+    -- a.C&&(b=a.get("n"))&&(b=Bpa[0](b),a.set("n",b),Bpa.length||iha(""))}};
+    -- var Bpa=[iha];
+    local callsite = js_extract( js, '[^;]*%.set%("n",[^};]*' )
+    if not callsite then
+        vlc.msg.dbg( "Couldn't extract YouTube video throttling parameter descrambling function name" )
+        return nil
+    end
+
+    -- Try direct function name from following clause
+    local descrambler = string.match( callsite, '%.set%("n",.%),...?%.length||(...?)%(' )
+    local itm = nil
+    if not descrambler then
+        -- Try from main call site
+        descrambler = string.match( callsite, '[=%(,&|]([a-zA-Z0-9_$%[%]]+)%(.%),.%.set%("n",' )
+        if descrambler then
+            -- Check if this is only an intermediate variable
+            itm = string.match( descrambler, '^([^%[%]]+)%[' )
+            if itm then
+                descrambler = nil
+            end
+        else
+            -- Last chance: intermediate variable in following clause
+            itm = string.match( callsite, '%.set%("n",.%),(...?)%.length' )
+        end
+    end
+
+    if not descrambler and itm then
+        -- Resolve intermediate variable
+        descrambler = js_extract( js, 'var '..itm..'=%[(...?)[%],]' )
+    end
+
     if not descrambler then
         vlc.msg.dbg( "Couldn't extract YouTube video throttling parameter descrambling function name" )
         return nil