feat: add PromotionRequired to MoveResult and detect promotion in processMove

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

modules/core/src/main/scala/de/nowchess/chess/controller/GameController.scala

@@ -1,6 +1,7 @@
 package de.nowchess.chess.controller
 
 import de.nowchess.api.board.{Board, Color, File, Piece, Rank, Square}
+import de.nowchess.api.move.PromotionPiece
 import de.nowchess.chess.logic.*
 
 // ---------------------------------------------------------------------------
@@ -14,6 +15,14 @@ object MoveResult:
   case object NoPiece                                                                   extends MoveResult
   case object WrongColor                                                                extends MoveResult
   case object IllegalMove                                                               extends MoveResult
+  case class  PromotionRequired(
+    from: Square,
+    to: Square,
+    boardBefore: Board,
+    historyBefore: GameHistory,
+    captured: Option[Piece],
+    turn: Color
+  ) extends MoveResult
   case class  Moved(newBoard: Board, newHistory: GameHistory, captured: Option[Piece], newTurn: Color)      extends MoveResult
   case class  MovedInCheck(newBoard: Board, newHistory: GameHistory, captured: Option[Piece], newTurn: Color) extends MoveResult
   case class  Checkmate(winner: Color)                                                  extends MoveResult
@@ -45,6 +54,9 @@ object GameController:
               case Some(_) =>
                 if !MoveValidator.isLegal(board, history, from, to) then
                   MoveResult.IllegalMove
+                else if MoveValidator.isPromotionMove(board, from, to) then
+                  val captured = board.pieceAt(to)
+                  MoveResult.PromotionRequired(from, to, board, history, captured, turn)
                 else
                   val castleOpt = if MoveValidator.isCastle(board, from, to)
                                   then Some(MoveValidator.castleSide(from, to))

modules/core/src/test/scala/de/nowchess/chess/controller/GameControllerTest.scala

@@ -3,6 +3,7 @@ package de.nowchess.chess.controller
 import de.nowchess.api.board.*
 import de.nowchess.api.game.CastlingRights
 import de.nowchess.chess.logic.{CastleSide, GameHistory}
+import de.nowchess.chess.notation.FenParser
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
 
@@ -293,3 +294,30 @@ class GameControllerTest extends AnyFunSuite with Matchers:
         newBoard.pieceAt(Square(File.E, Rank.R3)) shouldBe Some(Piece.BlackPawn)  // capturing pawn placed
         captured shouldBe Some(Piece.WhitePawn)
       case other => fail(s"Expected Moved but got $other")
+
+  // ──── pawn promotion detection ───────────────────────────────────────────
+
+  test("processMove detects white pawn reaching R8 and returns PromotionRequired"):
+    val board = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
+    val result = GameController.processMove(board, GameHistory.empty, Color.White, "e7e8")
+    result should matchPattern { case _: MoveResult.PromotionRequired => }
+    result match
+      case MoveResult.PromotionRequired(from, to, _, _, _, turn) =>
+        from should be (sq(File.E, Rank.R7))
+        to   should be (sq(File.E, Rank.R8))
+        turn should be (Color.White)
+      case _ => fail("Expected PromotionRequired")
+
+  test("processMove detects black pawn reaching R1 and returns PromotionRequired"):
+    val board = FenParser.parseBoard("8/8/8/8/4K3/8/4p3/8").get
+    val result = GameController.processMove(board, GameHistory.empty, Color.Black, "e2e1")
+    result should matchPattern { case _: MoveResult.PromotionRequired => }
+
+  test("processMove detects pawn capturing to back rank as PromotionRequired with captured piece"):
+    val board = FenParser.parseBoard("3q4/4P3/8/8/8/8/8/8").get
+    val result = GameController.processMove(board, GameHistory.empty, Color.White, "e7d8")
+    result should matchPattern { case _: MoveResult.PromotionRequired => }
+    result match
+      case MoveResult.PromotionRequired(_, _, _, _, captured, _) =>
+        captured should be (Some(Piece(Color.Black, PieceType.Queen)))
+      case _ => fail("Expected PromotionRequired")