From 204d7acddc210d3177574be2fd66d8ba0804613e Mon Sep 17 00:00:00 2001
From: Jesse McDonald <nybble41@gmail.com>
Date: Fri, 24 Apr 2020 23:16:21 -0500
Subject: [PATCH] add the ability to detect checkmate without taking the king

---
 js/pacosako.js    | 42 +++++++++++++++++++++++++++++++++---------
 js/pacosako_ui.js | 10 ++++++++--
 2 files changed, 41 insertions(+), 11 deletions(-)

diff --git a/js/pacosako.js b/js/pacosako.js
index f57a881..113fb39 100644
--- a/js/pacosako.js
+++ b/js/pacosako.js
@@ -4,7 +4,8 @@ import {Iterator} from './iterator.js';
 
 /* Game states */
 const PLAYING = 'playing';
-const ENDED = 'ended';
+const RESIGNED = 'resigned';
+const CHECKMATE = 'checkmate';
 
 /* Sides */
 const LIGHT = 'light';
@@ -393,7 +394,7 @@ function addHistory(game) {
       result += '(' + move.promotion.toUpperCase() + ')';
    }
 
-   if (move.took === KING) {
+   if (game.status === CHECKMATE) {
       result += '#';
    } else if (game.isInCheck()) {
       result += '+';
@@ -936,7 +937,31 @@ class Game {
       this._redo = [];
 
       if (took === KING) {
-         this._status = ENDED;
+         this._status = CHECKMATE;
+      } else if (this._history && this.isInCheck(this._player)) {
+         /*
+          * NOTE: Preemptive checkmate detection is not performed on
+          * simulated games (without history) to prevent recursion.
+          */
+
+         let canEscape = false;
+
+         for (const tryFrom of this._board.findPieces(this._player, true)) {
+            for (const tryTo of this.legalMoves(this._player, tryFrom)) {
+               if (!this.isDeadEnd(tryFrom, tryTo)) {
+                  canEscape = true;
+                  break;
+               }
+            }
+
+            if (canEscape) {
+               break;
+            }
+         }
+
+         if (!canEscape) {
+            this._status = CHECKMATE;
+         }
       }
 
       addHistory(this);
@@ -960,7 +985,7 @@ class Game {
       this._checkCache = {};
       this._moves.push(move);
       this._redo = [];
-      this._status = ENDED;
+      this._status = RESIGNED;
 
       addHistory(this);
    }
@@ -974,11 +999,10 @@ class Game {
    }
 
    get winner() {
-      const move = this.lastMove;
-      if (move && move.resign) {
+      if (this._status === RESIGNED) {
          return otherSide(this.lastMove.side);
-      } else if (move && move.took === KING) {
-         return move.side;
+      } else if (this._status === CHECKMATE) {
+         return this.lastMove.side;
       } else {
          return null;
       }
@@ -1063,7 +1087,7 @@ export default {
    Board, Game,
 
    /* Game States */
-   PLAYING, ENDED,
+   PLAYING, RESIGNED, CHECKMATE,
 
    /* Sides */
    LIGHT, DARK,
diff --git a/js/pacosako_ui.js b/js/pacosako_ui.js
index 7ed07c1..58558c6 100644
--- a/js/pacosako_ui.js
+++ b/js/pacosako_ui.js
@@ -369,7 +369,9 @@ $(function (){
       }
 
       if (winner) {
-         if (lastMove && lastMove.resign) {
+         if (game.status === PS.CHECKMATE) {
+            msg += 'Checkmate! ';
+         } else if (lastMove && lastMove.resign) {
             msg += (lastMove.side === PS.LIGHT ? 'Light' : 'Dark') + ' player resigned. ';
          }
          msg += (winner === PS.LIGHT ? 'Light' : 'Dark') + ' player won!';
@@ -486,7 +488,11 @@ $(function (){
       const winner = currentGame.winner;
       const lastMove = currentGame.lastMove || {};
       const lastMeta = lastMove.meta || {};
-      const status = !winner ? null : (lastMove.took === PS.KING) ? 'mate' : 'ended';
+      const status =
+         (currentGame.status === PS.PLAYING) ? null :
+         (currentGame.status === PS.CHECKMATE) ? 'checkmate' :
+         (currentGame.status === PS.RESIGNED) ? 'resigned' :
+         'ended';
 
       const meta = {
          lightName,