From 9184c8f1b15a6ac77fe91c1b7f607f4e4aebf8af Mon Sep 17 00:00:00 2001
From: Janis <janis-e@gmx.de>
Date: Tue, 31 Mar 2026 20:01:35 +0200
Subject: [PATCH] feat: add PGN export support for pawn promotion notation
 (=Q/=R/=B/=N)

Extend PgnExporter.moveToAlgebraic() to append the promotion piece suffix
(=Q, =R, =B, =N) for moves where a pawn is promoted. Existing castling
and normal moves remain unaffected.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
---
 .../nowchess/chess/notation/PgnExporter.scala | 10 ++++-
 .../chess/notation/PgnExporterTest.scala      | 37 +++++++++++++++++++
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/modules/core/src/main/scala/de/nowchess/chess/notation/PgnExporter.scala b/modules/core/src/main/scala/de/nowchess/chess/notation/PgnExporter.scala
index 8eb4d1c..a7f6449 100644
--- a/modules/core/src/main/scala/de/nowchess/chess/notation/PgnExporter.scala
+++ b/modules/core/src/main/scala/de/nowchess/chess/notation/PgnExporter.scala
@@ -1,6 +1,7 @@
 package de.nowchess.chess.notation
 
 import de.nowchess.api.board.*
+import de.nowchess.api.move.PromotionPiece
 import de.nowchess.chess.logic.{CastleSide, GameHistory, HistoryMove}
 
 object PgnExporter:
@@ -32,4 +33,11 @@ object PgnExporter:
     move.castleSide match
       case Some(CastleSide.Kingside)  => "O-O"
       case Some(CastleSide.Queenside) => "O-O-O"
-      case None => s"${move.from}${move.to}"
+      case None =>
+        val base = s"${move.from}${move.to}"
+        move.promotionPiece match
+          case Some(PromotionPiece.Queen)  => s"$base=Q"
+          case Some(PromotionPiece.Rook)   => s"$base=R"
+          case Some(PromotionPiece.Bishop) => s"$base=B"
+          case Some(PromotionPiece.Knight) => s"$base=N"
+          case None                        => base
diff --git a/modules/core/src/test/scala/de/nowchess/chess/notation/PgnExporterTest.scala b/modules/core/src/test/scala/de/nowchess/chess/notation/PgnExporterTest.scala
index 133252b..6c39aa6 100644
--- a/modules/core/src/test/scala/de/nowchess/chess/notation/PgnExporterTest.scala
+++ b/modules/core/src/test/scala/de/nowchess/chess/notation/PgnExporterTest.scala
@@ -1,6 +1,7 @@
 package de.nowchess.chess.notation
 
 import de.nowchess.api.board.*
+import de.nowchess.api.move.PromotionPiece
 import de.nowchess.chess.logic.{GameHistory, HistoryMove, CastleSide}
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
@@ -63,3 +64,39 @@ class PgnExporterTest extends AnyFunSuite with Matchers:
 
     pgn.contains("O-O-O") shouldBe true
   }
+
+  test("exportGame encodes promotion to Queen as =Q suffix") {
+    val history = GameHistory()
+      .addMove(HistoryMove(Square(File.E, Rank.R7), Square(File.E, Rank.R8), None, Some(PromotionPiece.Queen)))
+    val pgn = PgnExporter.exportGame(Map.empty, history)
+    pgn should include ("e7e8=Q")
+  }
+
+  test("exportGame encodes promotion to Rook as =R suffix") {
+    val history = GameHistory()
+      .addMove(HistoryMove(Square(File.E, Rank.R7), Square(File.E, Rank.R8), None, Some(PromotionPiece.Rook)))
+    val pgn = PgnExporter.exportGame(Map.empty, history)
+    pgn should include ("e7e8=R")
+  }
+
+  test("exportGame encodes promotion to Bishop as =B suffix") {
+    val history = GameHistory()
+      .addMove(HistoryMove(Square(File.E, Rank.R7), Square(File.E, Rank.R8), None, Some(PromotionPiece.Bishop)))
+    val pgn = PgnExporter.exportGame(Map.empty, history)
+    pgn should include ("e7e8=B")
+  }
+
+  test("exportGame encodes promotion to Knight as =N suffix") {
+    val history = GameHistory()
+      .addMove(HistoryMove(Square(File.E, Rank.R7), Square(File.E, Rank.R8), None, Some(PromotionPiece.Knight)))
+    val pgn = PgnExporter.exportGame(Map.empty, history)
+    pgn should include ("e7e8=N")
+  }
+
+  test("exportGame does not add suffix for normal moves") {
+    val history = GameHistory()
+      .addMove(HistoryMove(Square(File.E, Rank.R2), Square(File.E, Rank.R4), None, None))
+    val pgn = PgnExporter.exportGame(Map.empty, history)
+    pgn should include ("e2e4")
+    pgn should not include ("=")
+  }