[gnome-chess/gnome-3-8] Insufficient material fixes

[Jason Clinton <jclinton src gnome org>]

commit ae752829e774cfd3112f0b72aa96119b457581bf
Author: Michael Catanzaro <mike catanzaro gmail com>
Date:   Wed Jan 2 19:09:32 2013 -0600

    Insufficient material fixes
    
    Although two knights cannot FORCE a checkmate, the opponent can
    blunder. This position is not a draw.
    
    Also, if each side has one minor piece (unless they are two
    Bishops on the same color) the game is - surprisingly - not drawn.
    With the extra piece you could wind up in a checkmate that's not
    possible if the King is on his own.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=691053
    (cherry picked from commit 3a0a4d6a896474a8f6681442f958be0069c8f83f)

 src/chess-game.vala      | 10 ++++++++--
 src/test-chess-game.vala | 19 ++++++++++++++++++-
 2 files changed, 26 insertions(+), 3 deletions(-)
---
diff --git a/src/chess-game.vala b/src/chess-game.vala
index 96c01e7..39e386f 100644
--- a/src/chess-game.vala
+++ b/src/chess-game.vala
@@ -970,8 +970,8 @@ public class ChessState
                 }
             }
 
-            /* Three knights versus king can checkmate */
-            if (white_knight_count > 2 || black_knight_count > 2)
+            /* Two knights versus king can checkmate (though not against an optimal opponent) */
+            if (white_knight_count > 1 || black_knight_count > 1)
                 return true;
 
             /* Bishop and knight versus king can checkmate */
@@ -985,6 +985,12 @@ public class ChessState
                 return true;
             if (black_bishop_on_white_square && black_bishop_on_black_square)
                 return true;
+
+            /* King and minor piece vs. King and knight is surprisingly not a draw */
+            if ((white_bishop_count > 0 || white_knight_count > 0) && black_knight_count > 0)
+                return true;
+            if ((black_bishop_count > 0 || black_knight_count > 0) && white_knight_count > 0)
+                return true;
         }
 
         return false;
diff --git a/src/test-chess-game.vala b/src/test-chess-game.vala
index eb339d7..89f5e53 100644
--- a/src/test-chess-game.vala
+++ b/src/test-chess-game.vala
@@ -127,10 +127,27 @@ class GlChess
         test_good_move ("k7/8/7R/8/8/8/8/1R6 w - - 0 1", "Rh7",
                         "k7/7R/8/8/8/8/8/1R6 b - - 1 1", ChessResult.DRAW, ChessRule.STALEMATE);
 
-        /* Insufficient material */
+        /* Insufficient material - King vs. King */
         test_good_move ("k7/7p/7K/8/8/8/8/8 w - - 0 1", "Kxh7",
                         "k7/7K/8/8/8/8/8/8 b - - 0 1", ChessResult.DRAW, ChessRule.INSUFFICIENT_MATERIAL);
 
+        /* Insufficient material - King and knight vs. King */
+        test_good_move ("k7/7p/7K/8/8/8/8/7N w - - 0 1", "Kxh7",
+                        "k7/7K/8/8/8/8/8/7N b - - 0 1", ChessResult.DRAW, ChessRule.INSUFFICIENT_MATERIAL);
+        /* Sufficient if a knight on each side */
+        test_good_move("k7/7p/7K/8/8/8/8/6Nn w - - 0 1", "Kxh7",
+                       "k7/7K/8/8/8/8/8/6Nn b - - 0 1");
+        /* A bishop would suffice as well */
+        test_good_move("k7/7p/7K/8/8/8/8/6Nb w - - 0 1", "Kxh7",
+                       "k7/7K/8/8/8/8/8/6Nb b - - 0 1");
+
+        /* Insufficient material - King and n same-color bishops vs. King and n other-color bishops */
+        test_good_move("k2b1b1b/6bp/7K/5B1B/8/8/8/8 w - - 0 1", "Kxh7",
+                       "k2b1b1b/6bK/8/5B1B/8/8/8/8 b - - 0 1", ChessResult.DRAW, 
ChessRule.INSUFFICIENT_MATERIAL);
+        /* Sufficient if a bishop is on each color */
+        test_good_move("k2b1b1b/6bp/7K/6BB/8/8/8/8 w - - 0 1", "Kxh7",
+                       "k2b1b1b/6bK/8/6BB/8/8/8/8 b - - 0 1");
+
         // FIXME: Need to be able to test claim draw
 
         /* Claim draw due to 50 move rule */