Requirements

Let's delve into designing the core engine for an online card game. Imagine building the foundation for a poker game, or perhaps something more novel. We're not concerned with the UI/UX or the networking aspects (that's HLD). Instead, we focus on the game's internal mechanics: managing players, handling card decks, enforcing rules, and determining the winner. This is more than just shuffling cards; it's about creating a robust, extensible, and maintainable system that can handle variations in game rules and accommodate future features without major refactoring. Think about how to represent cards, decks, hands, players, and game states in an object-oriented manner. Consider how actions like dealing, betting, and folding are triggered and processed. How do you represent and evaluate different hand rankings? We're not aiming for a perfect, production-ready system in a single interview, but rather a demonstration of sound design principles and the ability to reason about trade-offs. # Requirements ## Functional Requirements * **Game Setup:** * The system must support the creation of a game instance with a defined number of players. * Each player should have a unique identifier and a name. * A standard 52-card deck must be created and shuffled. (Or other deck types for extensions). * The system should support specifying different game variants (e.g., Texas Hold'em, Five Card Draw) through configuration, impacting rules for dealing, betting rounds, and hand evaluation. * Initial player balances should be configurable. * **Game Play:** * The system must be able to deal cards to players according to the game variant's rules. * Players must be able to perform actions: Bet, Raise, Call, Fold, Check (if applicable). * The system must track the current state of the game (e.g., pre-flop, flop, turn, river in Texas Hold'em). * The system must manage the pot and track individual player bets. * The system must enforce game rules, such as minimum bet sizes, maximum raises, and valid action sequences. * **Hand Evaluation:** * The system must be able to evaluate player hands based on the game variant's ranking rules. * The system must be able to determine the winner(s) of a round, considering ties and splitting the pot accordingly. * **Game End:** * The system should handle the end of a round, distributing the pot to the winner(s). * The system should handle the end of the game (e.g., when a player runs out of money). * **Support multiple tables/games concurrently** ## Non-Functional Requirements * **Extensibility:** The design should be easily extensible to support new card games with different rules, hand rankings, and betting structures. The addition of new game types should not require significant changes to existing code. * **Modularity:** The system should be composed of well-defined, loosely coupled modules, making it easier to understand, test, and maintain. * **Testability:** The code should be designed to be easily testable, with clear separation of concerns and dependencies. Unit tests should be possible for individual components, such as hand evaluation logic or betting rules. * **Thread Safety:** The system must be thread-safe, allowing multiple games to be played concurrently without data corruption or race conditions. Consider how to handle concurrent access to shared resources, such as the deck or player balances. Avoid deadlocks. * **SOLID Principles:** The design should adhere to SOLID principles (Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion) to promote maintainability and reduce code complexity. * **Performance:** Hand evaluation, especially for many players, needs to be reasonably efficient. Consider caching strategies for evaluated hands. * **Error Handling:** Implement robust error handling for invalid game states, illegal actions, and unexpected situations. ## Core Entities * **Card:** Represents a single playing card with a suit and rank. * **Deck:** Represents a collection of cards, typically a standard 52-card deck. Should support shuffling, dealing, and potentially creating new decks. * **Hand:** Represents a player's hand of cards. * **Player:** Represents a player in the game, with attributes like name, ID, balance, and hand. * **Game:** Represents a single instance of a card game, managing players, the deck, the pot, and the game state. * **GameState:** Represents the current stage of the game (e.g., PreFlop, Flop, Turn, River). * **Action:** Represents a player's action (Bet, Raise, Call, Fold, Check). * **BettingRound:** Represents a round of betting within a game state. * **HandEvaluator:** An interface/abstract class responsible for evaluating the hand ranking of a given hand based on the game rules. Implementations would vary by game type (e.g., Texas Hold'em, Five Card Draw). * **RuleEngine:** An interface responsible for defining game-specific rules, such as dealing cards, betting constraints, valid actions, and winning conditions. Implementations would vary by game type.

Design for online card game say like poker or any other game.

Requirements

Interview Simulation

Functional Requirements

💡 Interview Tip

Non-Functional Requirements

Core Entity Identification

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