Design Chess Game

Functional Requirements:

• Allow two players to play a standard chess game online.
• Enforce all standard chess rules (legal moves, turn order, check/checkmate, stalemate, castling, en passant, pawn promotion, draw conditions).
• Track and display the current board state and move history to both players in real time.
• Support basic time control (e.g., each player has a fixed amount of time for the whole game).
• Allow players to resign or offer/accept a draw.
• Persist completed games for later review.

Non-Functional Requirements:

• Ensure low-latency move updates between players (moves should appear within a second).
• Support multiple concurrent games (hundreds to thousands, depending on deployment scale).
• Provide basic user authentication (players must log in to play).
• Prevent illegal moves and enforce turn order on the server side.
• System should be reliable: a single server failure should not impact all games.
• Secure user data and communication (e.g., use encrypted connections).

Out of Scope (for this design):

• Advanced features like tournaments, matchmaking by rating, spectator mode, or chat.
• Mobile app or desktop client specifics.
• Anti-cheating mechanisms beyond server-side move validation.