[gnome-chess] Support new fivefold repetition and 75 move draw conditions

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 19a65b04e621ae8111f7bc41fe5e3c2d8a2e0fe1
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Wed May 4 15:18:13 2016 -0500

    Support new fivefold repetition and 75 move draw conditions
    
    On July 1, 2014 the FIDE Laws of Chess were updated to add two new
    automatic draw conditions. These are the same as the threefold
    repetition and 50 move rules, except they take effect automatically
    rather than optionally.
    
    http://www.fide.com/component/handbook/?id=171&view=article
    
    https://bugzilla.gnome.org/show_bug.cgi?id=766005

 lib/chess-game.vala  |   44 +++++++++++++++++++++++++++++++++++++-------
 src/gnome-chess.vala |    8 ++++++++
 2 files changed, 45 insertions(+), 7 deletions(-)
---
diff --git a/lib/chess-game.vala b/lib/chess-game.vala
index 683f32d..e342e72 100644
--- a/lib/chess-game.vala
+++ b/lib/chess-game.vala
@@ -25,8 +25,10 @@ public enum ChessRule
     CHECKMATE,
     STALEMATE,
     FIFTY_MOVES,
+    SEVENTY_FIVE_MOVES,
     TIMEOUT,
     THREE_FOLD_REPETITION,
+    FIVE_FOLD_REPETITION,
     INSUFFICIENT_MATERIAL,
     RESIGN,
     ABANDONMENT,
@@ -183,13 +185,25 @@ public class ChessGame : Object
         if (result != ChessResult.IN_PROGRESS)
         {
             stop (result, rule);
+            return;
         }
-        else
+
+        if (is_five_fold_repeat ())
+        {
+            stop (ChessResult.DRAW, ChessRule.FIVE_FOLD_REPETITION);
+            return;
+        }
+
+        /* Note this test must occur after the test for checkmate in current_state.get_result (). */
+        if (is_seventy_five_move_rule_fulfilled ())
         {
-            if (_clock != null)
-                _clock.active_color = current_player.color;
-            turn_started (current_player);
+            stop (ChessResult.DRAW, ChessRule.SEVENTY_FIVE_MOVES);
+            return;
         }
+
+        if (_clock != null)
+            _clock.active_color = current_player.color;
+        turn_started (current_player);
     }
 
     private void undo_cb (ChessPlayer player)
@@ -233,23 +247,39 @@ public class ChessGame : Object
         return count;
     }
 
-    public bool is_three_fold_repeat ()
+    private bool is_n_fold_repeat (int n)
     {
         foreach (var state in move_stack)
         {
-            if (state_repeated_times (state) >= 3)
+            if (state_repeated_times (state) >= n)
                 return true;
         }
 
         return false;
     }
 
+    public bool is_three_fold_repeat ()
+    {
+        return is_n_fold_repeat (3);
+    }
+
+    public bool is_five_fold_repeat ()
+    {
+        return is_n_fold_repeat (5);
+    }
+
     public bool is_fifty_move_rule_fulfilled ()
     {
-        /* Fifty moves per player without capture or pawn advancement */
+        /* Fifty moves *per player* without capture or pawn advancement */
         return current_state.halfmove_clock >= 100;
     }
 
+    public bool is_seventy_five_move_rule_fulfilled ()
+    {
+        /* 75 moves *per player* without capture or pawn advancement */
+        return current_state.halfmove_clock >= 150;
+    }
+
     public bool can_claim_draw ()
     {
         return is_fifty_move_rule_fulfilled () || is_three_fold_repeat ();
diff --git a/src/gnome-chess.vala b/src/gnome-chess.vala
index 66e2cf7..70b7458 100644
--- a/src/gnome-chess.vala
+++ b/src/gnome-chess.vala
@@ -1314,6 +1314,10 @@ Copyright © 2015–2016 Sahil Sareen""";
             /* Window subtitle when the game is drawn due to the fifty move rule */
             reason = _("No piece was taken or pawn moved in fifty moves.");
             break;
+        case ChessRule.SEVENTY_FIVE_MOVES:
+            /* Window subtitle when the game is drawn due to the 75 move rule */
+            reason = _("No piece was taken or pawn moved in 75 moves.");
+            break;
         case ChessRule.TIMEOUT:
             if (game.result == ChessResult.WHITE_WON)
                 /* Window subtitle when the game ends due to Black's clock stopping */
@@ -1328,6 +1332,10 @@ Copyright © 2015–2016 Sahil Sareen""";
             /* Window subtitle when the game is drawn due to the three-fold-repetition rule */
             reason = _("The same board state has occurred three times.");
             break;
+        case ChessRule.FIVE_FOLD_REPETITION:
+            /* Window subtitle when the game is drawn due to the five-fold-repetition rule */
+            reason = _("The same board state has occurred five times.");
+            break;
         case ChessRule.INSUFFICIENT_MATERIAL:
             /* Window subtitle when the game is drawn due to the insufficient material rule */
             reason = _("Neither player can checkmate.");