From e28ea59095088cadc6bee17f613cad121928b1a5 Mon Sep 17 00:00:00 2001
From: Jesse McDonald <nybble41@gmail.com>
Date: Sun, 5 Apr 2020 05:24:26 -0500
Subject: [PATCH] block castling out of check

---
 js/pacosako.js | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/js/pacosako.js b/js/pacosako.js
index 1cf091f..cb70079 100644
--- a/js/pacosako.js
+++ b/js/pacosako.js
@@ -504,17 +504,29 @@ class Game {
          if (from === (side === DARK ? 'e8' : 'e1')) {
             const row = from[1];
 
+            /* memoize isInCheck(); may not need it and don't want to look twice */
+            /* with any other piece this would be recursive, but kings can't capture */
+            let inCheck = () => {
+               const check = this.isInCheck(side);
+               inCheck = () => check;
+               return check;
+            };
+
             if (this._castling[side].king &&
                   board.isEmpty('f' + row) &&
                   board.isEmpty('g' + row)) {
-               yield 'g' + row;
+               if (!inCheck()) {
+                  yield 'g' + row;
+               }
             }
 
             if (this._castling[side].queen &&
                   board.isEmpty('d' + row) &&
                   board.isEmpty('c' + row) &&
                   board.isEmpty('b' + row)) {
-               yield 'c' + row;
+               if (!inCheck()) {
+                  yield 'c' + row;
+               }
             }
          }
       } else if (type === QUEEN) {
@@ -609,12 +621,16 @@ class Game {
       /* start with the opponent's unpaired pieces, the ones that can capture */
       let queue = [];
       for (const from of sim._board.findPieces(other, true, false)) {
-         if (sim.isLegalMove(other, from, king, true)) {
-            /* this piece can directly capture the king */
-            return true;
-         }
+         /* this next condition is needed to avoid recursion through legalMoves() */
+         /* kings can't capture anything anyway, so they can be skipped */
+         if (sim._board.getPiece(other, from) !== KING) {
+            if (sim.isLegalMove(other, from, king, true)) {
+               /* this piece can directly capture the king */
+               return true;
+            }
 
-         queue.push({ game: sim, from });
+            queue.push({ game: sim, from });
+         }
       }
 
       /* arbitrary limit, but a human player would probably miss a 7-move chain too */