Implements four core enhancements: FEN notation support, move undo/redo with state snapshots, minimax AI opponent with alpha-beta pruning, and comprehensive documentation for extracting the chess engine as a reusable library.

FEN Import/Export

• FENParser utility class supporting all 6 FEN components (piece placement, active color, castling rights, en passant, halfmove clock, fullmove number)
• importFromFEN(String) and exportToFEN() methods on ChessGame
• REST endpoints: POST /importFEN, GET /exportFEN
• Round-trip tested with validation for all edge cases
• Test Coverage: FENParserTest (10 tests)

ChessGame game = new ChessGame();
game.importFromFEN("rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1");
String fen = game.exportToFEN(); // Exports current position

Undo/Redo

• GameStateSnapshot immutable snapshots capturing complete game state (board, turn, castling rights, en passant, captured pieces, halfmove clock)
• State history maintained in ChessGame for unlimited undo depth
• Redo history cleared on new moves
• Works with all move types: castling, en passant, promotion, captures
• REST endpoints: GET /undo, GET /redo, GET /undoRedoStatus
• Test Coverage: UndoRedoTest (11 tests)

game.MoveController(new Position(2, 5), new Position(4, 5)); // e4
game.undo(); // Back to initial position
game.redo(); // Forward to e4 position

AI Opponent

• BoardEvaluator with material evaluation (standard piece values) and positional bonuses (pawn advancement, knight centralization)
• ChessAI minimax implementation with alpha-beta pruning (default depth: 3 ply)
• ~0.5-2 second move generation on typical positions
• REST endpoint: GET /aiMove returns fromRow,fromCol,toRow,toCol,score
• Test Coverage: BoardEvaluatorTest (10 tests) + ChessAITest (13 tests)
• Bug Fix: Fixed Position mutation issue in AI search that caused ArrayIndexOutOfBoundsException

ChessAI.AIMove move = ChessAI.findBestMove(game, 3);
game.MoveController(move.from, move.to);

Chess Engine Extraction

• CHESS_ENGINE_EXTRACTION_GUIDE.md: Three extraction options (multi-module Gradle, Maven artifact, JAR)
• CHESS_ENGINE_API.md: Complete API reference with examples
• Core components identified: domain classes (Chessboard, ChessGame), models, utilities (FENParser, PGNExporter), AI
• Zero framework dependencies in core chess logic

Implementation Notes

• Zero new external dependencies
• All existing tests pass, no breaking changes
• Complete test coverage: 44+ tests across all new functionality
  • FEN Parser: 10 tests
  • Undo/Redo: 11 tests
  • Board Evaluator: 10 tests
  • Chess AI: 13 tests
• All tests passing
• Frontend integration (UI controls) deferred but APIs ready

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.