From 58a962cf98b0a2abf5a58e222b53e43be0b11971 Mon Sep 17 00:00:00 2001
From: Janis <janis-e@gmx.de>
Date: Sat, 28 Mar 2026 18:48:08 +0100
Subject: [PATCH] feat: add PGN exporter for game notation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 .../nowchess/chess/notation/PgnExporter.scala | 35 ++++++++++++++
 .../chess/notation/PgnExporterTest.scala      | 48 +++++++++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100644 modules/core/src/main/scala/de/nowchess/chess/notation/PgnExporter.scala
 create mode 100644 modules/core/src/test/scala/de/nowchess/chess/notation/PgnExporterTest.scala

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
new file mode 100644
index 0000000..8eb4d1c
--- /dev/null
+++ b/modules/core/src/main/scala/de/nowchess/chess/notation/PgnExporter.scala
@@ -0,0 +1,35 @@
+package de.nowchess.chess.notation
+
+import de.nowchess.api.board.*
+import de.nowchess.chess.logic.{CastleSide, GameHistory, HistoryMove}
+
+object PgnExporter:
+
+  /** Export a game with headers and history to PGN format. */
+  def exportGame(headers: Map[String, String], history: GameHistory): String =
+    val headerLines = headers.map { case (key, value) =>
+      s"""[$key "$value"]"""
+    }.mkString("\n")
+
+    val moveText = if history.moves.isEmpty then ""
+    else
+      val groupedMoves = history.moves.zipWithIndex.groupBy(_._2 / 2)
+      val moveLines = for (moveNumber, movePairs) <- groupedMoves.toList.sortBy(_._1) yield
+        val moveNum = moveNumber + 1
+        val whiteMoveStr = movePairs.find(_._2 % 2 == 0).map(p => moveToAlgebraic(p._1)).getOrElse("")
+        val blackMoveStr = movePairs.find(_._2 % 2 == 1).map(p => moveToAlgebraic(p._1)).getOrElse("")
+        if blackMoveStr.isEmpty then s"$moveNum. $whiteMoveStr"
+        else s"$moveNum. $whiteMoveStr $blackMoveStr"
+
+      moveLines.mkString(" ") + " *"
+
+    if headerLines.isEmpty then moveText
+    else if moveText.isEmpty then headerLines
+    else s"$headerLines\n\n$moveText"
+
+  /** Convert a HistoryMove to algebraic notation. */
+  private def moveToAlgebraic(move: HistoryMove): String =
+    move.castleSide match
+      case Some(CastleSide.Kingside)  => "O-O"
+      case Some(CastleSide.Queenside) => "O-O-O"
+      case None => s"${move.from}${move.to}"
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
new file mode 100644
index 0000000..1869141
--- /dev/null
+++ b/modules/core/src/test/scala/de/nowchess/chess/notation/PgnExporterTest.scala
@@ -0,0 +1,48 @@
+package de.nowchess.chess.notation
+
+import de.nowchess.api.board.*
+import de.nowchess.chess.logic.{GameHistory, HistoryMove, CastleSide}
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class PgnExporterTest extends AnyFunSuite with Matchers:
+
+  test("export empty game") {
+    val headers = Map("Event" -> "Test", "White" -> "A", "Black" -> "B")
+    val history = GameHistory.empty
+    val pgn = PgnExporter.exportGame(headers, history)
+
+    pgn.contains("[Event \"Test\"]") shouldBe true
+    pgn.contains("[White \"A\"]") shouldBe true
+    pgn.contains("[Black \"B\"]") shouldBe true
+  }
+
+  test("export single move") {
+    val headers = Map("Event" -> "Test", "White" -> "A", "Black" -> "B")
+    val history = GameHistory()
+      .addMove(HistoryMove(Square(File.E, Rank.R2), Square(File.E, Rank.R4), None))
+    val pgn = PgnExporter.exportGame(headers, history)
+
+    pgn.contains("1. e2e4") shouldBe true
+  }
+
+  test("export castling") {
+    val headers = Map("Event" -> "Test")
+    val history = GameHistory()
+      .addMove(HistoryMove(Square(File.E, Rank.R1), Square(File.G, Rank.R1), Some(CastleSide.Kingside)))
+    val pgn = PgnExporter.exportGame(headers, history)
+
+    pgn.contains("O-O") shouldBe true
+  }
+
+  test("export game sequence") {
+    val headers = Map("Event" -> "Test", "White" -> "A", "Black" -> "B", "Result" -> "1-0")
+    val history = GameHistory()
+      .addMove(HistoryMove(Square(File.E, Rank.R2), Square(File.E, Rank.R4), None))
+      .addMove(HistoryMove(Square(File.C, Rank.R7), Square(File.C, Rank.R5), None))
+      .addMove(HistoryMove(Square(File.G, Rank.R1), Square(File.F, Rank.R3), None))
+    val pgn = PgnExporter.exportGame(headers, history)
+
+    pgn.contains("1. e2e4 c7c5") shouldBe true
+    pgn.contains("2. g1f3") shouldBe true
+  }