Add stalemate detection, castling validation, move history tracking, PGN export, and draw detection

[Copilot]

Chess Engine Enhancement - Complete ✅

All required features have been successfully implemented and tested:

✅ Completed Features

1. Stalemate Detection

   • Implemented isStalemate() in Chessboard class
   • Added DrawByStalemate state to GameState enum
   • Integrated into game flow in ChessGame.MoveController()
   • Full test coverage in DrawDetectionTest

2. Castling with Full Validation

   • Implemented kingside and queenside castling for both colors
   • Validates all castling rules:
     • King and rook haven't moved
     • No pieces between king and rook
     • King not in check
     • King doesn't move through check
     • King doesn't land in check
   • Track piece movements to prevent illegal castling
   • Comprehensive test coverage in CastlingTest (7 tests)
   • Enabled previously disabled testCastlingThroughCheckIsRejected() test

3. Pinned Piece Validation

   • Already implemented via filterMovesLeavingKingInCheck()
   • All edge cases handled correctly
   • Test testPinnedPieceCannotExposeKing() passes

4. Move History Tracking

   • Created Move class to represent chess moves
   • Tracks all moves in ChessGame.moveHistory
   • Records piece, positions, captures, promotions, special moves
   • API endpoint /moveHistory to retrieve history
   • Used for PGN export and draw detection

5. PGN Export

   • Created PGNExporter utility class
   • Implements standard PGN format with headers
   • Converts moves to algebraic notation
   • Handles castling notation (O-O, O-O-O)
   • Handles pawn captures, promotions
   • Determines game result (1-0, 0-1, 1/2-1/2, *)
   • API endpoint /exportPGN to get PGN string
   • Test coverage in PGNExporterTest (4 tests)

6. Draw Detection

   • Stalemate: Player not in check with no legal moves
   • 50-move rule: Tracks half-moves since pawn move or capture
   • Threefold repetition: Simplified board hash comparison
   • Added draw states: DrawByStalemate, DrawByRepetition, DrawByFiftyMove
   • All integrated into move validation

📊 Test Results

• Total Tests: 40 (all passing ✅)
• No regressions in existing functionality
• CodeQL Security Scan: 0 alerts ✅

🔧 API Additions

• GET /moveHistory - Returns list of all moves
• GET /exportPGN - Returns game in PGN format

📝 Technical Details

• Avoided infinite recursion in castling validation by separating getCandidateMoves() from getValidMoves()
• Castling moves validated separately from normal king moves
• Proper tracking of piece movements for castling eligibility
• Move history enables future features like game replay and analysis

📖 Documentation Updates

• Updated README to reflect all implemented features
• Moved completed features from "Future Improvements" to "Recently Implemented"
• Added new API endpoints to REST API documentation with example curl commands
• Updated main feature description to highlight new capabilities (stalemate, draw conditions, move history)
• Removed completed items from "Known Limitations" section

Original prompt

This is a must, please develop:

•  Stalemate Detection - Currently not implemented
•  Castling Through Check - May not be fully validated (see ChessRulesTest)
•  Pinned Piece Validation - Edge cases may exist (see ChessRulesTest)
•  Move History - Track all moves in a game
•  PGN Export - Save games in standard chess notation
   Move History Export - No PGN/FEN notation support
  Draw Detection - Stalemate, threefold repetition, 50-move rule not implemented
  Castling Through Check - May not be fully validated (see ChessRulesTest)
  Pinned Piece Validation - Edge cases may exist (see ChessRulesTest)
  Move History - Track all moves in a game
  PGN Export - Save games in standard chess notation
  Castling Through Check - May not be fully validated (see ChessRulesTest)
  Pinned Piece Validation - Edge cases may exist (see ChessRulesTest)
  Move History - Track all moves in a game
  PGN Export - Save games in standard chess notation

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[mgierschdev]

@copilot Continue where you left

[Copilot]

@copilot Continue where you left

I've completed the implementation by updating the README documentation to reflect all the features that were implemented:

✅ Updated main feature list to include stalemate, draw conditions, and move history
✅ Moved completed features from "Future Improvements" to "Recently Implemented" section
✅ Added new API endpoints (/moveHistory and /exportPGN) to REST API documentation
✅ Added example curl commands for the new endpoints
✅ Removed completed items from "Known Limitations"

All features are now fully implemented, tested (40 tests passing), and documented. The PR is ready for review. Commit: f3f3302