From fec602aca74e889984a62a9d202213429a31f6b9 Mon Sep 17 00:00:00 2001
From: LQ63 <lkhermann@web.de>
Date: Wed, 8 Apr 2026 08:07:20 +0200
Subject: [PATCH] feat(io): FastParse FEN

Added Shared Parser support
---
 .../de/nowchess/io/fen/FenParserSupport.scala | 32 +++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 modules/io/src/main/scala/de/nowchess/io/fen/FenParserSupport.scala

diff --git a/modules/io/src/main/scala/de/nowchess/io/fen/FenParserSupport.scala b/modules/io/src/main/scala/de/nowchess/io/fen/FenParserSupport.scala
new file mode 100644
index 0000000..ea33502
--- /dev/null
+++ b/modules/io/src/main/scala/de/nowchess/io/fen/FenParserSupport.scala
@@ -0,0 +1,32 @@
+package de.nowchess.io.fen
+
+import de.nowchess.api.board.*
+
+private[fen] object FenParserSupport:
+
+  sealed trait RankToken
+  case class PieceToken(piece: Piece) extends RankToken
+  case class EmptyToken(count: Int)   extends RankToken
+
+  val charToPieceType: Map[Char, PieceType] = Map(
+    'p' -> PieceType.Pawn,
+    'r' -> PieceType.Rook,
+    'n' -> PieceType.Knight,
+    'b' -> PieceType.Bishop,
+    'q' -> PieceType.Queen,
+    'k' -> PieceType.King
+  )
+
+  def buildSquares(rank: Rank, tokens: Seq[RankToken]): Option[List[(Square, Piece)]] =
+    tokens.foldLeft(Option((List.empty[(Square, Piece)], 0))):
+      case (None, _) => None
+      case (Some((acc, fileIdx)), PieceToken(piece)) =>
+        if fileIdx > 7 then None
+        else
+          val sq = Square(File.values(fileIdx), rank)
+          Some((acc :+ (sq -> piece), fileIdx + 1))
+      case (Some((acc, fileIdx)), EmptyToken(n)) =>
+        val next = fileIdx + n
+        if next > 8 then None
+        else Some((acc, next))
+    .flatMap { case (squares, total) => if total == 8 then Some(squares) else None }