Fix Makruk/Makpong

[vchess.git] / client / src / variants / Makpong.js

diff --git a/client/src/variants/Makpong.js b/client/src/variants/Makpong.js
index 0576665..885de3e 100644 (file)
--- a/client/src/variants/Makpong.js
+++ b/client/src/variants/Makpong.js
@@ -4,11 +4,47 @@ export class MakpongRules extends MakrukRules {
 
   filterValid(moves) {
     const color = this.turn;
-    if (this.underCheck(color)) {
-      // Filter out all moves involving king
-      return super.filterValid(moves.filter(m => m.vanish[0].p != V.KING));
-    }
-    return super.filterValid(moves);
+    if (!this.underCheck(color)) return super.filterValid(moves);
+    // Filter out all moves involving king, except for capturing a
+    // potential attacker.
+    const pawnAttack = (color == 'w' ? -1 : 1);
+    return super.filterValid(moves.filter(m => {
+      const p = (m.vanish.length == 2 ? m.vanish[1].p : null);
+      return (
+        m.vanish[0].p != V.KING ||
+        (
+          m.vanish.length == 2 &&
+          (
+            (
+              p == V.PAWN &&
+              m.end.x - m.start.x == pawnAttack &&
+              Math.abs(m.end.y - m.start.y) == 1
+            )
+            ||
+            (
+              p == V.ROOK &&
+              (m.end.x == m.start.x || m.end.y == m.start.y)
+            )
+            ||
+            (
+              [V.PROMOTED, V.QUEEN].includes(p) &&
+              m.end.x != m.start.x && m.end.y != m.start.y
+            )
+            ||
+            (
+              p == V.BISHOP &&
+              (
+                m.end.x - m.start.x == pawnAttack ||
+                (
+                  m.end.x - m.start.x == -pawnAttack &&
+                  Math.abs(m.end.y - m.start.y) == 1
+                )
+              )
+            )
+          )
+        )
+      );
+    }));
   }
 
 };