SwiftChess

SwiftChess is a chess engine written in Swift.

Features

Move validation
AI with three difficulty levels
Callbacks for check, checkmate and stalemate
Supports castling
Supports En Passent
Supports pawn promotion
Asyncronous AI move calculation

SwiftChess doesn't provide any UI, just all of the logic required to create a chess game. The example project contains a complete UIKit UI with touch handling that you start from if you like.

Example

The example application contains a complete implementation of SwiftChess.

Run Example/Example.xcodeproj

Basic Use

Start a game

// Make a human player
let whitePlayer = Human(color: .white)

// ... or an AI Player
let blackPlayer = AIPlayer(color: .black, configuration: AIConfiguration(difficulty: .hard))

// Create a game       
let game = Game(firstPlayer: whitePlayer, secondPlayer: blackPlayer)

Make a move

if let player = game.currentPlayer as? Human {

	let currentLocation = BoardLocation(x: 4, y: 1)
	let newLocation = BoardLocation(x: 4, y: 2)

	try! player.movePiece(from: currentLocation,
                        to: newLocation)
}

Tell the AI to make a move

if let player =  game.currentPlayer as? AIPlayer {
	player.makeMoveAsync()
}

Then just wait for the callbacks!

extension GameViewController: GameDelegate {

	func gameDidMovePiece(game: Game, piece: Piece, toLocation: BoardLocation) {
        // Move piece on board
    }
    
    func gameDidRemovePiece(game: Game, piece: Piece, location: BoardLocation) {
        // Remove piece from board 
    }
    
    func gameDidTransformPiece(game: Game, piece: Piece, location: BoardLocation) {
    	// A pawn was promoted!
    }
    
    func gameWonByPlayer(game: Game, player: Player) {
    	ShowAlert("Checkmate!")
    }
    
    func gameEndedInStaleMate(game: Game) {
     	ShowAlert("Stalemate!")
    }
    
    func gameDidChangeCurrentPlayer(game: Game) {
    	// Make another move        
    }
}

Persistence

The entire state of a SwiftChess game can be converted to and initialised from a Dictionary.

Get a snapshot of the current state:

let dictionary: [String: Any] = game.dictionaryRepresentation

Initialise a game with a previous snapshot:

let game = Game(dictionary: dictionary)

The returned dictionary stores all the information required to create a 'save game' feature. The player colors, AI difficulty, piece positions etc.

You can serialize this to JSON, save it to disk, send it over the network etc.

Other stuff

Make a castling move

if game.board.canColorCastle(color: .white, side: .kingSide) {
	player.performCastleMove(side: .kingSide)
}

Support pawn promotion

func promotedTypeForPawn(location: BoardLocation, 
                         player: Human, 
                         possiblePromotions: [Piece.PieceType], 
                         callback: @escaping (Piece.PieceType) -> Void) {

	// Show UI for the user to select one of the possible promotion types
	// then call the handler
	
	// ...or some games just promote to a queen
	callback(.queen)
}

Author

Follow me on twitter @SteveBarnegren

License

SwiftChess is available under the MIT license. See the LICENSE file for more info.

chessboy/SwiftChess