[gnome-chess] Fix check for engine timeout in untimed games

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 5ca2ab0440fce3a891b04019705a94996b2723cf
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Sun Dec 6 09:56:33 2020 -0600

    Fix check for engine timeout in untimed games
    
    We currently give the engine 10 seconds to move, and end the game with
    an engine error if it takes longer than that, to avoid the game stalling
    forever if the engine breaks. But we use the chess clock to run this
    check, meaning it doesn't work in untimed games. And games are untimed
    by default. Oops.
    
    Fix it by not relying on the chess clock.
    
    Fixes #54

 src/gnome-chess.vala | 55 +++++++++++++++++++++++++---------------------------
 1 file changed, 26 insertions(+), 29 deletions(-)
---
diff --git a/src/gnome-chess.vala b/src/gnome-chess.vala
index 2edb413..03c8d5d 100644
--- a/src/gnome-chess.vala
+++ b/src/gnome-chess.vala
@@ -74,7 +74,7 @@ public class ChessApplication : Gtk.Application
     private ChessPlayer? opponent = null;
     private ChessPlayer? human_player = null;
     private ChessEngine? opponent_engine = null;
-    private int engine_timeout_counter = 10;
+    private uint engine_timeout_source = 0;
     private string copyrights = """Copyright © 2010–2013 Robert Ancell
 Copyright © 2013–2020 Michael Catanzaro
 Copyright © 2015–2016 Sahil Sareen""";
@@ -739,6 +739,7 @@ Copyright © 2015–2016 Sahil Sareen""";
             black_engine != null && game.current_player.color == Color.BLACK)
         {
             assert (opponent_engine != null);
+            update_engine_timeout ();
             opponent_engine.move ();
         }
 
@@ -927,35 +928,8 @@ Copyright © 2015–2016 Sahil Sareen""";
          */
     }
 
-    private void check_engine_timeout ()
-        requires (engine_timeout_counter >= 0)
-        ensures (engine_timeout_counter >= 0)
-    {
-        if (opponent_engine == null)
-            return;
-
-        if (pgn_game.white_ai != null && game.current_player.color == Color.WHITE ||
-            pgn_game.black_ai != null && game.current_player.color == Color.BLACK)
-        {
-            engine_timeout_counter -= 1;
-
-            if (engine_timeout_counter == 0)
-            {
-                // Chess engine did not move for a long time
-                // End the game assuming a buggy engine
-                engine_error_cb (opponent_engine);
-            }
-        }
-        else
-        {
-            // Reset the engine timeout
-            engine_timeout_counter = 10;
-        }
-    }
-
     private void game_clock_tick_cb (ChessClock clock)
     {
-        check_engine_timeout ();
         white_time_label.queue_draw ();
         black_time_label.queue_draw ();
     }
@@ -1190,6 +1164,26 @@ Copyright © 2015–2016 Sahil Sareen""";
         model.set (iter, 0, label, -1);
     }
 
+    private void update_engine_timeout ()
+    {
+        if (engine_timeout_source != 0)
+        {
+            Source.remove(engine_timeout_source);
+            engine_timeout_source = 0;
+        }
+
+        if (pgn_game.white_ai != null && game.current_player.color == Color.WHITE ||
+            pgn_game.black_ai != null && game.current_player.color == Color.BLACK)
+        {
+            engine_timeout_source = Timeout.add_seconds (10, () => {
+                engine_timeout_source = 0;
+                warning ("Engine did not move for 10 seconds! Game over.");
+                engine_error_cb (opponent_engine);
+                return Source.REMOVE;
+            });
+        }
+    }
+
     private void game_move_cb (ChessGame game, ChessMove move)
     {
         /* Warning: this callback is invoked several times when loading a game. */
@@ -1227,7 +1221,7 @@ Copyright © 2015–2016 Sahil Sareen""";
 
         view.queue_draw ();
 
-        /* Remaining work goes in a timeout to give the game widget a chance to
+        /* This work goes in a timeout to give the game widget a chance to
          * redraw first, so the pieces are shown to move before displaying the
          * claim draw dialog. */
         var started = !starting && game.is_started;
@@ -1245,6 +1239,9 @@ Copyright © 2015–2016 Sahil Sareen""";
 
             return Source.REMOVE;
         });
+
+        if (started)
+            update_engine_timeout ();
     }
 
     private void game_undo_cb (ChessGame game)