Core Engine

The Backgammon.Core project contains all game logic with zero external dependencies.

Key Classes

GameEngine

The main game orchestrator that enforces all backgammon rules.

var game = new GameEngine("White", "Red");
game.StartNewGame();

// Roll dice
game.RollDice();

// Get valid moves
var moves = game.GetValidMoves();

// Execute a move
game.ExecuteMove(moves[0]);

// End turn
game.EndTurn();

Key Properties:

• CurrentPlayer - Player whose turn it is
• RemainingMoves - Dice values left to use
• GameOver - Whether the game has ended
• Winner - The winning player (if game over)

Board

Represents the 24-point backgammon board.

// Points are 1-24
// Point 0 = bar
// Point 25 = bear off zone

var point = board.GetPoint(6);
int checkers = point.Checkers.Count;
CheckerColor color = point.Color;

Movement Directions:

• White: Moves from point 24 → point 1 (descending)
• Red: Moves from point 1 → point 24 (ascending)

Home Boards:

• White home: Points 1-6
• Red home: Points 19-24

Match

Tracks multi-game matches with scoring.

var match = new Match(7); // First to 7 points

match.RecordGameResult(new GameResult
{
    Winner = CheckerColor.White,
    WinType = WinType.Gammon,
    PointsScored = 4 // 2 for gammon × 2 for cube
});

bool isComplete = match.IsComplete;
bool isCrawford = match.IsCrawfordGame;

Crawford Rule: When a player reaches match point minus one, the next game is the "Crawford game" where no doubling is allowed.

DoublingCube

Manages stake doubling.

var cube = new DoublingCube();

// Initial value is 1, centered
cube.Offer(CheckerColor.White);
cube.Accept(CheckerColor.Red); // Now at 2, Red owns

// Only the non-owner can offer
cube.Offer(CheckerColor.Red);
cube.Accept(CheckerColor.White); // Now at 4, White owns

Move

Represents a checker movement.

var move = new Move(from: 6, to: 3);

// Special cases
var barEntry = new Move(from: 0, to: 22); // Entering from bar
var bearOff = new Move(from: 3, to: 25);  // Bearing off

Game Rules

Valid Move Requirements

1. Bar Priority: If checkers are on the bar, they must enter first
2. Open Point: Can only land on points with ≤1 opponent checker
3. Hitting: Landing on a single opponent checker sends it to the bar
4. Bear Off: Only when all checkers are in home board
5. Forced Move: If only one die can be used, must use the larger value

Winning Conditions

Type	Condition	Points
Normal	Opponent has borne off ≥1 checker	1 × cube
Gammon	Opponent has 0 checkers borne off	2 × cube
Backgammon	Gammon + checker on bar or in winner's home	3 × cube

Testing the Engine

[Fact]
public void TestBasicMove()
{
    var game = new GameEngine();
    game.StartNewGame();

    // Manipulate board for testing
    game.Board.GetPoint(1).Checkers.Clear();
    game.Board.GetPoint(1).AddChecker(CheckerColor.White);

    // Set specific dice
    game.Dice.SetDice(3, 4);
    game.RemainingMoves.Clear();
    game.RemainingMoves.AddRange(game.Dice.GetMoves());

    var moves = game.GetValidMoves();
    Assert.NotEmpty(moves);
}