feat: I/O json export import, tests should be 100%

modules/ui/chess_game.json

@@ -0,0 +1,41 @@
+{
+  "metadata": {
+    "event": "Game",
+    "players": {
+      "white": "White Player",
+      "black": "Black Player"
+    },
+    "date": "2026-04-06",
+    "result": "*"
+  },
+  "gameState": {
+    "board": [{"square": "g8", "color": "Black", "piece": "Knight"}, {"square": "d8", "color": "Black", "piece": "Queen"}, {"square": "f8", "color": "Black", "piece": "Bishop"}, {"square": "b2", "color": "White", "piece": "Pawn"}, {"square": "c1", "color": "White", "piece": "Bishop"}, {"square": "c7", "color": "Black", "piece": "Pawn"}, {"square": "f7", "color": "Black", "piece": "Pawn"}, {"square": "b7", "color": "Black", "piece": "Pawn"}, {"square": "b1", "color": "White", "piece": "Knight"}, {"square": "h8", "color": "Black", "piece": "Rook"}, {"square": "a1", "color": "White", "piece": "Rook"}, {"square": "g2", "color": "White", "piece": "Pawn"}, {"square": "e1", "color": "White", "piece": "King"}, {"square": "c2", "color": "White", "piece": "Pawn"}, {"square": "h2", "color": "White", "piece": "Pawn"}, {"square": "a8", "color": "Black", "piece": "Rook"}, {"square": "f1", "color": "White", "piece": "Bishop"}, {"square": "d6", "color": "Black", "piece": "Pawn"}, {"square": "a2", "color": "White", "piece": "Pawn"}, {"square": "d1", "color": "White", "piece": "Queen"}, {"square": "e2", "color": "White", "piece": "Pawn"}, {"square": "c8", "color": "Black", "piece": "Bishop"}, {"square": "a7", "color": "Black", "piece": "Pawn"}, {"square": "b8", "color": "Black", "piece": "Knight"}, {"square": "d2", "color": "White", "piece": "Pawn"}, {"square": "e8", "color": "Black", "piece": "King"}, {"square": "f4", "color": "White", "piece": "Pawn"}, {"square": "g7", "color": "Black", "piece": "Pawn"}, {"square": "h7", "color": "Black", "piece": "Pawn"}, {"square": "e7", "color": "Black", "piece": "Pawn"}, {"square": "h1", "color": "White", "piece": "Rook"}, {"square": "g1", "color": "White", "piece": "Knight"}],
+    "turn": "White",
+    "castlingRights": {
+    "whiteKingSide": true,
+    "whiteQueenSide": true,
+    "blackKingSide": true,
+    "blackQueenSide": true
+  },
+    "enPassantSquare": null,
+    "halfMoveClock": 0
+  },
+  "moveHistory": "[Event \"?\"]\n[White \"?\"]\n[Black \"?\"]\n[Result \"*\"]\n\n1. f4 d6 *",
+  "moves": [
+    {
+      "from": "f2",
+      "to": "f4",
+      "type": {"type": "normal", "isCapture": false}
+    },
+    {
+      "from": "d7",
+      "to": "d6",
+      "type": {"type": "normal", "isCapture": false}
+    }
+  ],
+  "capturedPieces": {
+    "byWhite": ["Pawn"],
+    "byBlack": ["Pawn"]
+  },
+  "timestamp": "2026-04-06T11:39:00.746137480Z[UTC]"
+}

modules/ui/src/main/scala/de/nowchess/ui/gui/ChessBoardView.scala

@@ -16,7 +16,11 @@ import de.nowchess.chess.command.{MoveCommand, MoveResult}
 import de.nowchess.chess.engine.GameEngine
 import de.nowchess.io.fen.{FenExporter, FenParser}
 import de.nowchess.io.pgn.{PgnExporter, PgnParser}
-import de.nowchess.io.{GameContextExport, GameContextImport}
+import de.nowchess.io.json.{JsonExporter, JsonParser}
+import de.nowchess.io.{GameContextExport, GameContextImport, GameFileService, FileSystemGameService}
+import java.nio.file.Paths
+import scalafx.stage.FileChooser
+import scalafx.stage.FileChooser.ExtensionFilter
 
 /** ScalaFX chess board view that displays the game state.
  *  Uses chess sprites and color palette.
@@ -124,6 +128,22 @@ class ChessBoardView(val stage: Stage, private val engine: GameEngine) extends B
             style = "-fx-background-radius: 8; -fx-background-color: #B9DAC4;"
           }
         )
+      },
+      new HBox {
+        spacing = 10
+        alignment = Pos.Center
+        children = Seq(
+          new Button("JSON Export") {
+            font = Font.font(comicSansFontFamily, 12)
+            onAction = _ => doJsonExport()
+            style = "-fx-background-radius: 8; -fx-background-color: #B9C4DA;"
+          },
+          new Button("JSON Import") {
+            font = Font.font(comicSansFontFamily, 12)
+            onAction = _ => doJsonImport()
+            style = "-fx-background-radius: 8; -fx-background-color: #C4B9DA;"
+          }
+        )
       }
     )
   }
@@ -289,6 +309,45 @@ class ChessBoardView(val stage: Stage, private val engine: GameEngine) extends B
   private def doPgnImport(): Unit =
     doImport(PgnParser, "PGN")
 
+  private def doJsonExport(): Unit =
+    val fileChooser = new FileChooser {
+      title = "Export Game as JSON"
+      initialFileName = "chess_game.json"
+      extensionFilters.add(new ExtensionFilter("JSON files (*.json)", "*.json"))
+      extensionFilters.add(new ExtensionFilter("All files", "*.*"))
+    }
+    
+    val selectedFile = fileChooser.showSaveDialog(stage)
+    if selectedFile != null then
+      val result = FileSystemGameService.saveGameToFile(
+        engine.context,
+        selectedFile.toPath,
+        JsonExporter
+      )
+      result match
+        case Right(_) => showMessage(s"✓ Game saved to: ${selectedFile.getName}")
+        case Left(err) => showMessage(s"⚠️ Error saving file: $err")
+
+  private def doJsonImport(): Unit =
+    val fileChooser = new FileChooser {
+      title = "Import Game from JSON"
+      extensionFilters.add(new ExtensionFilter("JSON files (*.json)", "*.json"))
+      extensionFilters.add(new ExtensionFilter("All files", "*.*"))
+    }
+    
+    val selectedFile = fileChooser.showOpenDialog(stage)
+    if selectedFile != null then
+      val result = FileSystemGameService.loadGameFromFile(
+        selectedFile.toPath,
+        JsonParser
+      )
+      result match
+        case Right(gameContext) =>
+          engine.loadPosition(gameContext)
+          showMessage(s"✓ Game loaded from: ${selectedFile.getName}")
+        case Left(err) =>
+          showMessage(s"⚠️ Error: $err")
+
   private def doExport(exporter: GameContextExport, formatName: String): Unit = {
     val exported = exporter.exportGameContext(engine.context)
     showCopyDialog(s"$formatName Export", exported)