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// Define a trait for game state management
trait GameStateHandler {
    fn handle_step(&self, json_payload: &str) -> Result<GameState, Box<dyn Error>>;
}

// Implement the trait for each state
impl GameStateHandler for CardExchange {
    fn handle_step(&self, json_payload: &str) -> Result<GameState, Box<dyn Error>> {
        // Logic for handling CardExchange state
        // ...
    }
}

impl GameStateHandler for RoundInProgress {
    fn handle_step(&self, json_payload: &str) -> Result<GameState, Box<dyn Error>> {
        // Logic for handling RoundInProgress state
        // ...
    }
}

impl GameStateHandler for RoundFinished {
    fn handle_step(&self, json_payload: &str) -> Result<GameState, Box<dyn Error>> {
        // Logic for handling RoundFinished state
        // ...
    }
}

// Main play function
pub fn play<G: GameStateHandler>(&self, input_handler: fn() -> String) -> Result<(), Box<dyn Error>> {
    let mut game_state = GameState::get_initial_state(&self.players);
    
    loop {
        let json_payload = input_handler();

        game_state = match game_state {
            GameState::CardExchange(step) => step.handle_step(&json_payload)?,
            GameState::RoundInProgress(step) => step.handle_step(&json_payload)?,
            GameState::RoundFinished(step) => step.handle_step(&json_payload)?,
            _ => {
                eprintln!("Unhandled game state");
                return Err(Box::new(GameError::new("Unhandled game state")));
            }
        };

        if game_state.is_final_state(&self.settings.max_score) {
            break;
        }
    }

    Ok(())
}

// Assume we have some GameError type defined for handling custom game-related errors
#[derive(Debug)]
struct GameError {
    message: String,
}

impl GameError {
    fn new(msg: &str) -> GameError {
        GameError { message: msg.to_owned() }
    }
}

impl std::fmt::Display for GameError {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "{}", self.message)
    }
}

impl Error for GameError {}

// Assume GameState has a method to check if it's the final state
impl GameState {
    fn is_final_state(&self, max_score: &i32) -> bool {
        // Logic to determine if the game has reached the final state
        // ...
    }
}