Chess

Design a two-player chess game: board, pieces, legal move generation, check and checkmate detection, special moves, and undo. It's hard mainly because of rule validation, and it's a great showcase for polymorphism and the Command pattern.

Requirements

Functional

• 8 x 8 board with the standard initial setup; White moves first.
• Each piece type moves by its own rules; captures by moving onto an opponent's piece.
• Reject illegal moves, including moves that leave your own king in check.
• Detect check, checkmate, and stalemate.
• Special moves: castling, en passant, pawn promotion.
• Undo/redo moves; move history in algebraic notation.
• Optional: clocks, draw by threefold repetition and the 50-move rule, resignation.

Non-functional

• Clear separation between rules, board state, and UI/IO.
• Adding a variant piece or rule should not require rewriting the game loop.
• Move validation fast enough for interactive play (a bot is a follow-up).