show endgame glyph on another piece when there is no king - closes #21971

Antichess and horde can end with a side that has no king, so the
result glyph had nothing to sit on. Fall back to the queen, rook,
bishop, knight and pawn, in that order.

ui/lib/src/game/endgame.ts

@@ -44,12 +44,14 @@ export function endgameShapesForNode(
   return endgameShapes(node.fen, result.winner, result.status);
 }
 
-export function findKingSquare(fen: FEN, color: Color): Key | undefined {
+const glyphRoles: Role[] = ['king', 'queen', 'rook', 'bishop', 'knight', 'pawn'];
-  const king = parseFen(fen).unwrap(
+
-    setup => setup.board.kingOf(color),
+export function findGlyphSquare(fen: FEN, color: Color): Key | undefined {
+  const square = parseFen(fen).unwrap(
+    setup => glyphRoles.map(role => setup.board.pieces(color, role).first()).find(sq => sq !== undefined),
     _ => undefined,
   );
-  return king === undefined ? undefined : makeSquare(king);
+  return square === undefined ? undefined : makeSquare(square);
 }
 
 const loserGlyph = (status: StatusName | undefined): EndgameGlyph =>
@@ -82,10 +84,10 @@ export function endgameShapes(
 
   const shapes: DrawShape[] = [];
   const add = (color: Color, glyph: EndgameGlyph) => {
-    const king = findKingSquare(fen, color);
+    const square = findGlyphSquare(fen, color);
-    if (king)
+    if (square)
       shapes.push({
-        orig: king,
+        orig: square,
         brush: '',
         customSvg: { html: endgameGlyphs[glyph](0), center: 'orig' },
       });

ui/lib/tests/endgame.test.ts

@@ -0,0 +1,26 @@
+import assert from 'node:assert/strict';
+import { test } from 'node:test';
+
+import { endgameShapes } from '../src/game/endgame';
+import type { StatusName } from '../src/game/status';
+
+const origs = (fen: FEN, winner: Color | undefined, status: StatusName) =>
+  endgameShapes(fen, winner, status).map(shape => shape.orig);
+
+test('glyph goes on the king when there is one', () => {
+  assert.deepStrictEqual(origs('4k3/8/8/8/8/8/8/Q3K3 w - - 0 1', 'black', 'resign'), ['e1']);
+});
+
+test('glyph falls back to the strongest piece without a king', () => {
+  assert.deepStrictEqual(origs('8/8/8/8/8/8/8/6N1 b - - 0 28', 'black', 'variantEnd'), ['g1']);
+  assert.deepStrictEqual(origs('8/8/8/8/8/8/2P5/1NR5 b - - 0 40', 'black', 'variantEnd'), ['c1']);
+  assert.deepStrictEqual(origs('8/8/8/8/8/8/2P5/1N6 b - - 0 40', 'black', 'variantEnd'), ['b1']);
+});
+
+test('draw glyphs show for a side without a king', () => {
+  assert.deepStrictEqual(origs('4k3/8/8/8/8/8/PPPPPPPP/8 w - - 0 1', undefined, 'stalemate'), ['a2', 'e8']);
+});
+
+test('no glyph for a side without pieces', () => {
+  assert.deepStrictEqual(origs('8/8/8/8/8/8/8/6N1 b - - 0 28', 'white', 'variantEnd'), []);
+});