Improve undo logic

Chess/Game.swift

@@ -65,17 +65,15 @@ extension Game {
  }
  }
 
- // MARK: Settings
+ // MARK: Game logic
 
- var playerIsHuman: Bool {
- switch turn {
+ func playerIsHuman(_ color: Color? = nil) -> Bool {
+ switch color ?? turn {
  case .white: return whiteIsHuman
  case .black: return blackIsHuman
  }
  }
 
- // MARK: Game logic
-
  func canSelectPiece(at position: Position) -> Bool {
  board.piece(at: position)?.color == turn
  }

Chess/ViewController.swift

@@ -82,7 +82,7 @@ class ViewController: UIViewController {
  self.updateUI()
  }, completion: { [weak self] _ in
  guard let self = self else { return }
- if !game.inProgress || self.game.playerIsHuman {
+ if self.game.playerIsHuman() || !self.game.playerIsHuman(game.turn.other) {
  self.update()
  } else {
  self.undo()
@@ -136,7 +136,7 @@ extension ViewController: BoardViewDelegate {
 
 private extension ViewController {
  var canUndo: Bool {
- (game.playerIsHuman || game.state == .checkMate) && game.inProgress
+ game.inProgress && (game.playerIsHuman() || game.playerIsHuman(game.turn.other))
  }
 
  func updateUI() {
@@ -189,7 +189,7 @@ private extension ViewController {
  }
 
  func makeComputerMove() {
- if !game.playerIsHuman, let move = game.nextMove(for: game.turn) {
+ if !game.playerIsHuman(), let move = game.nextMove(for: game.turn) {
  makeMove(move)
  } else {
  updateUI()
@@ -206,7 +206,7 @@ private extension ViewController {
  let kingPosition = game.kingPosition(for: oldGame.turn)
  let wasInCheck = game.pieceIsThreatened(at: kingPosition)
  let wasPromoted = !wasInCheck && game.canPromotePiece(at: move.to)
- let wasHuman = oldGame.playerIsHuman
+ let wasHuman = oldGame.playerIsHuman()
  if wasInCheck {
  game = oldGame
  }