fix: tactician arata betrayal move gen

.changeset/fix-arata-tactician-betrayal.md

@@ -0,0 +1,9 @@
+---
+'gungi.js': patch
+---
+
+Fix tactician arata betrayal generation when stacking onto a friendly-topped tower.
+
+- Allow `新謀(... )返X` move generation for this niche arata case.
+- Apply betrayal conversion and hand consumption correctly for arata betrayal moves.
+- Add regression coverage for both white and black variants.

src/gungi/move_gen.ts

@@ -156,20 +156,7 @@ export function generateMovesForSquare(square: string, fen: string) {
 
 				// betrayal
 				if (piece.type === pieceType.tactician && p.color !== piece.color) {
-					const enemies = t.filter((p) => p.color !== piece.color);
-					const playerHand = hand.filter((p) => p.color === piece.color);
-					const enemyCountMap = enemies.reduce((acc, e) => {
-						acc.set(e.type, (acc.get(e.type) ?? 0) + 1);
-						return acc;
-					}, new Map<PieceType, number>());
-
-					const betrayalOptions = Array.from(enemyCountMap.entries())
-						.filter(([type, count]) =>
-							playerHand.some((p) => p.type === type && p.count >= count)
-						)
-						.flatMap(([type]) => enemies.filter((e) => e.type === type));
-
-					const combos = generateCombinations(betrayalOptions);
+					const combos = getBetrayalCombos(t, hand, piece.color);
 					acc.push(
 						...combos.map((combo) =>
 							createMove(piece, `${s}-${p.tier + 1}`, fen, 'betray', combo)
@@ -250,6 +237,11 @@ export function generateArata(piece: HandPiece, fen: string) {
 				p.type !== pieceType.marshal)
 		) {
 			const t = (p?.tier ?? 0) + 1;
+			const tower = get(s, board);
+			const betrayalCombos =
+				piece.type === pieceType.tactician && tower
+					? getBetrayalCombos(tower, hand, piece.color)
+					: [];
 			const playerHandCount = hand
 				.filter((h) => h.color === piece.color)
 				.reduce((sum, h) => sum + h.count, 0);
@@ -259,10 +251,25 @@ export function generateArata(piece: HandPiece, fen: string) {
 				// If only 1 piece left, must end draft - no option to continue
 				if (!isLastPiece) {
 					acc.push(createMove(arata, `${s}-${t}`, fen, 'arata'));
+					acc.push(
+						...betrayalCombos.map((combo) =>
+							createMove(arata, `${s}-${t}`, fen, 'arata', combo)
+						)
+					);
 				}
 				acc.push(createMove(arata, `${s}-${t}`, fen, 'arata', [], true));
+				acc.push(
+					...betrayalCombos.map((combo) =>
+						createMove(arata, `${s}-${t}`, fen, 'arata', combo, true)
+					)
+				);
 			} else {
 				acc.push(createMove(arata, `${s}-${t}`, fen, 'arata'));
+				acc.push(
+					...betrayalCombos.map((combo) =>
+						createMove(arata, `${s}-${t}`, fen, 'arata', combo)
+					)
+				);
 			}
 		}
 
@@ -285,7 +292,9 @@ function createMove(
 	const tsuke =
 		type === 'tsuke' || (toTier !== 1 && toTier - piece.tier > 0) ? '付' : '';
 	const betray =
-		type === 'betray' ? `返${captured?.map((p) => p.type).join('')}` : '';
+		type === 'betray' || (type === 'arata' && captured && captured.length > 0)
+			? `返${captured?.map((p) => p.type).join('')}`
+			: '';
 	const draftDone = draftFinished ? '終' : '';
 
 	const move: Move = {
@@ -329,6 +338,10 @@ function makeMove(move: Move, fen: string) {
 		updateHand(move.captured!, hand, true);
 	} else if (move.type === 'arata') {
 		updateHand([to], hand);
+		if (move.captured?.length) {
+			convert(`${rank}-${file}`, move.captured, board);
+			updateHand(move.captured, hand, true);
+		}
 		if (move.draftFinished) {
 			drafting[move.color] = false;
 			if (move.color === 'b') drafting.w = false;
@@ -383,6 +396,29 @@ function generateCombinations<T>(items: T[]): T[][] {
 	return result;
 }
 
+function getBetrayalCombos(
+	tower: Piece[],
+	hand: HandPiece[],
+	color: Color
+): Piece[][] {
+	const enemies = tower.filter((p) => p.color !== color);
+	if (enemies.length === 0) return [];
+
+	const playerHand = hand.filter((p) => p.color === color);
+	const enemyCountMap = enemies.reduce((acc, e) => {
+		acc.set(e.type, (acc.get(e.type) ?? 0) + 1);
+		return acc;
+	}, new Map<PieceType, number>());
+
+	const betrayalOptions = Array.from(enemyCountMap.entries())
+		.filter(([type, count]) =>
+			playerHand.some((p) => p.type === type && p.count >= count)
+		)
+		.flatMap(([type]) => enemies.filter((e) => e.type === type));
+
+	return generateCombinations(betrayalOptions);
+}
+
 function getAttackedSquares(square: string, board: Board): string[] {
 	const piece = getTop(square, board);
 	if (!piece) return [];

test/rules-update.test.ts

@@ -205,4 +205,84 @@ describe('Rules Updates', () => {
 			expect(targets).not.toContain('7-7');
 		});
 	});
+
+	describe('Tactician arata betrayal', () => {
+		it('allows 新謀 to betray when arata onto a friendly-topped stack', () => {
+			const board = createEmptyBoard();
+			placeTower(board, '5-5', [
+				{ type: piece.soldier, color: 'b' },
+				{ type: piece.warrior, color: 'w' },
+			]);
+			placeTower(board, '1-1', [{ type: piece.marshal, color: 'b' }]);
+			placeTower(board, '9-9', [{ type: piece.marshal, color: 'w' }]);
+
+			const fen = encodeFEN({
+				board,
+				hand: [
+					{ type: piece.tactician, color: 'w', count: 1 },
+					{ type: piece.soldier, color: 'w', count: 1 },
+				],
+				turn: 'w',
+				mode: 'advanced',
+				drafting: { b: false, w: false },
+				moveNumber: 1,
+			});
+			const gungi = new Gungi(fen);
+
+			const sanMoves = getSanMoves(gungi);
+			expect(sanMoves).toContain('新謀(5-5-3)返兵');
+
+			gungi.move('新謀(5-5-3)返兵');
+
+			const movedTower = gungi.get('5-5');
+			expect(movedTower?.map((p) => p.type)).toStrictEqual(['兵', '侍', '謀']);
+			expect(movedTower?.every((p) => p.color === 'w')).toBe(true);
+
+			expect(
+				gungi.hand('w').find((h) => h.type === piece.tactician)
+			).toBeUndefined();
+			expect(
+				gungi.hand('w').find((h) => h.type === piece.soldier)
+			).toBeUndefined();
+		});
+
+		it('allows black 新謀 to betray when arata onto a friendly-topped stack', () => {
+			const board = createEmptyBoard();
+			placeTower(board, '5-5', [
+				{ type: piece.soldier, color: 'w' },
+				{ type: piece.warrior, color: 'b' },
+			]);
+			placeTower(board, '1-1', [{ type: piece.marshal, color: 'b' }]);
+			placeTower(board, '9-9', [{ type: piece.marshal, color: 'w' }]);
+
+			const fen = encodeFEN({
+				board,
+				hand: [
+					{ type: piece.tactician, color: 'b', count: 1 },
+					{ type: piece.soldier, color: 'b', count: 1 },
+				],
+				turn: 'b',
+				mode: 'advanced',
+				drafting: { b: false, w: false },
+				moveNumber: 1,
+			});
+			const gungi = new Gungi(fen);
+
+			const sanMoves = getSanMoves(gungi);
+			expect(sanMoves).toContain('新謀(5-5-3)返兵');
+
+			gungi.move('新謀(5-5-3)返兵');
+
+			const movedTower = gungi.get('5-5');
+			expect(movedTower?.map((p) => p.type)).toStrictEqual(['兵', '侍', '謀']);
+			expect(movedTower?.every((p) => p.color === 'b')).toBe(true);
+
+			expect(
+				gungi.hand('b').find((h) => h.type === piece.tactician)
+			).toBeUndefined();
+			expect(
+				gungi.hand('b').find((h) => h.type === piece.soldier)
+			).toBeUndefined();
+		});
+	});
 });