.idea/gradle.xml

@@ -14,6 +14,7 @@
             <option value="$PROJECT_DIR$/modules/core" />
             <option value="$PROJECT_DIR$/modules/io" />
             <option value="$PROJECT_DIR$/modules/rule" />
+            <option value="$PROJECT_DIR$/modules/server" />
             <option value="$PROJECT_DIR$/modules/ui" />
           </set>
         </option>

.idea/scala_compiler.xml

@@ -5,7 +5,7 @@
       <option name="deprecationWarnings" value="true" />
       <option name="uncheckedWarnings" value="true" />
     </profile>
-    <profile name="Gradle 2" modules="NowChessSystems.modules.core.main,NowChessSystems.modules.core.scoverage,NowChessSystems.modules.core.test,NowChessSystems.modules.io.main,NowChessSystems.modules.io.scoverage,NowChessSystems.modules.io.test,NowChessSystems.modules.rule.main,NowChessSystems.modules.rule.scoverage,NowChessSystems.modules.rule.test,NowChessSystems.modules.ui.main,NowChessSystems.modules.ui.scoverage,NowChessSystems.modules.ui.test">
+    <profile name="Gradle 2" modules="NowChessSystems.modules.core.main,NowChessSystems.modules.core.scoverage,NowChessSystems.modules.core.test,NowChessSystems.modules.io.main,NowChessSystems.modules.io.scoverage,NowChessSystems.modules.io.test,NowChessSystems.modules.rule.main,NowChessSystems.modules.rule.scoverage,NowChessSystems.modules.rule.test,NowChessSystems.modules.server.main,NowChessSystems.modules.server.scoverage,NowChessSystems.modules.server.test,NowChessSystems.modules.ui.main,NowChessSystems.modules.ui.scoverage,NowChessSystems.modules.ui.test">
       <option name="deprecationWarnings" value="true" />
       <option name="uncheckedWarnings" value="true" />
       <parameters>

build.gradle.kts

@@ -34,7 +34,13 @@ val versions = mapOf(
     "JAVAFX"                to "21.0.1",
     "JUNIT_BOM"             to "5.13.4",
     "SCALA_PARSER_COMBINATORS" to "2.4.0",
-    "FASTPARSE" to "3.0.2"
+    "FASTPARSE" to "3.0.2",
+    "HTTP4S" to "0.23.29",
+    "CIRCE"  to "0.14.10"
 )
 extra["VERSIONS"] = versions
 
+tasks.register("run") {
+    dependsOn(":modules:ui:run")
+}
+

modules/server/build.gradle.kts

@@ -0,0 +1,79 @@
+import org.gradle.jvm.tasks.Jar
+
+plugins {
+    id("scala")
+    id("org.scoverage") version "8.1"
+    application
+}
+
+group = "de.nowchess"
+version = "1.0-SNAPSHOT"
+
+@Suppress("UNCHECKED_CAST")
+val versions = rootProject.extra["VERSIONS"] as Map<String, String>
+
+repositories {
+    mavenCentral()
+}
+
+scala {
+    scalaVersion = versions["SCALA3"]!!
+}
+
+scoverage {
+    scoverageVersion.set(versions["SCOVERAGE"]!!)
+    excludedPackages.set(listOf("de.nowchess.server"))
+}
+
+application {
+    mainClass.set("de.nowchess.server.ServerApp")
+}
+
+tasks.withType<ScalaCompile> {
+    scalaCompileOptions.additionalParameters = listOf("-encoding", "UTF-8")
+}
+
+tasks.named<Jar>("jar") {
+    duplicatesStrategy = org.gradle.api.file.DuplicatesStrategy.EXCLUDE
+}
+
+dependencies {
+    implementation("org.scala-lang:scala3-compiler_3") {
+        version { strictly(versions["SCALA3"]!!) }
+    }
+    implementation("org.scala-lang:scala3-library_3") {
+        version { strictly(versions["SCALA3"]!!) }
+    }
+
+    implementation(project(":modules:api"))
+    implementation(project(":modules:core"))
+    implementation(project(":modules:io"))
+    implementation(project(":modules:rule"))
+
+    val http4s = versions["HTTP4S"]!!
+    val circe  = versions["CIRCE"]!!
+
+    implementation("org.http4s:http4s-ember-server_3:$http4s")
+    implementation("org.http4s:http4s-dsl_3:$http4s")
+    implementation("org.http4s:http4s-circe_3:$http4s")
+    implementation("io.circe:circe-core_3:$circe")
+    implementation("io.circe:circe-generic_3:$circe")
+    implementation("io.circe:circe-parser_3:$circe")
+
+    testImplementation(platform("org.junit:junit-bom:${versions["JUNIT_BOM"]!!}"))
+    testImplementation("org.junit.jupiter:junit-jupiter")
+    testImplementation("org.scalatest:scalatest_3:${versions["SCALATEST"]!!}")
+    testImplementation("co.helmethair:scalatest-junit-runner:${versions["SCALATEST_JUNIT"]!!}")
+
+    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
+}
+
+tasks.test {
+    useJUnitPlatform {
+        includeEngines("scalatest")
+        testLogging {
+            events("skipped", "failed")
+        }
+    }
+    finalizedBy(tasks.reportScoverage)
+}

modules/server/src/main/scala/de/nowchess/server/BoardRoutes.scala

@@ -0,0 +1,283 @@
+package de.nowchess.server
+
+import cats.effect.IO
+import org.http4s.*
+import org.http4s.dsl.io.*
+import org.http4s.circe.*
+import org.http4s.circe.CirceEntityDecoder.given
+import io.circe.syntax.*
+import de.nowchess.api.board.{Color, Square}
+import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
+import de.nowchess.api.player.{PlayerId, PlayerInfo}
+import de.nowchess.chess.engine.GameEngine
+import de.nowchess.chess.observer.InvalidMoveEvent
+import de.nowchess.io.fen.{FenExporter, FenParser}
+import de.nowchess.io.pgn.{PgnExporter, PgnParser}
+import JsonCodecs.given
+
+class BoardRoutes(registry: GameRegistry):
+
+  def routes: HttpRoutes[IO] = HttpRoutes.of[IO] {
+    case req @ POST -> Root / "api" / "board" / "game" / "import" / "fen" => importFen(req)
+    case req @ POST -> Root / "api" / "board" / "game" / "import" / "pgn" => importPgn(req)
+    case req @ POST -> Root / "api" / "board" / "game"                    => createGame(req)
+    case GET  -> Root / "api" / "board" / "game" / id                     => getGame(id)
+    case GET  -> Root / "api" / "board" / "game" / id / "stream"          => streamGame(id)
+    case POST -> Root / "api" / "board" / "game" / id / "move" / uci      => makeMove(id, uci)
+    case req @ GET -> Root / "api" / "board" / "game" / id / "moves"      => getLegalMoves(req, id)
+    case POST -> Root / "api" / "board" / "game" / id / "undo"            => undoMove(id)
+    case POST -> Root / "api" / "board" / "game" / id / "redo"            => redoMove(id)
+    case POST -> Root / "api" / "board" / "game" / id / "resign"          => resign(id)
+    case POST -> Root / "api" / "board" / "game" / id / "draw" / action   => drawAction(id, action)
+    case GET  -> Root / "api" / "board" / "game" / id / "export" / "fen"  => exportFen(id)
+    case GET  -> Root / "api" / "board" / "game" / id / "export" / "pgn"  => exportPgn(id)
+  }
+
+  // ─── Game lifecycle ────────────────────────────────────────────────────────
+
+  private def createGame(req: Request[IO]): IO[Response[IO]] =
+    req.as[CreateGameRequest]
+      .handleError(_ => CreateGameRequest())
+      .flatMap { body =>
+        val white = resolvePlayer(body.white, "white")
+        val black = resolvePlayer(body.black, "black")
+        registry.create(white, black).flatMap { id =>
+          registry.get(id).flatMap {
+            case None        => notFound(id)
+            case Some(entry) => Created(toGameFullDto(id, entry).asJson)
+          }
+        }
+      }
+
+  private def getGame(id: String): IO[Response[IO]] =
+    registry.get(id).flatMap {
+      case None        => notFound(id)
+      case Some(entry) => Ok(toGameFullDto(id, entry).asJson)
+    }
+
+  private def streamGame(id: String): IO[Response[IO]] =
+    registry.get(id).flatMap {
+      case None        => notFound(id)
+      case Some(entry) => Ok(GameFullEvent("gameFull", toGameFullDto(id, entry)).asJson)
+    }
+
+  private def resign(id: String): IO[Response[IO]] =
+    registry.get(id).flatMap {
+      case None                           => notFound(id)
+      case Some(entry) if entry.isOver    => badRequest("GAME_OVER", "Game is already over")
+      case Some(entry)                    =>
+        IO.blocking {
+          val winner = entry.engine.context.turn.opposite
+          entry.gameOver = Some(GameOverState.Resigned(winner, entry.engine.context))
+        }.flatMap(_ => Ok(OkDto().asJson))
+    }
+
+  // ─── Move-making ───────────────────────────────────────────────────────────
+
+  private def makeMove(id: String, uci: String): IO[Response[IO]] =
+    registry.get(id).flatMap {
+      case None                        => notFound(id)
+      case Some(entry) if entry.isOver => badRequest("GAME_OVER", "Game is already over")
+      case Some(entry)                 =>
+        IO.blocking {
+          entry.lastEvent = None
+          applyUci(entry, uci)
+          entry.lastEvent
+        }.flatMap {
+          case Some(InvalidMoveEvent(_, reason)) => badRequest("INVALID_MOVE", reason)
+          case _                                 => Ok(toGameStateDto(entry).asJson)
+        }
+    }
+
+  private def getLegalMoves(req: Request[IO], id: String): IO[Response[IO]] =
+    registry.get(id).flatMap {
+      case None                        => notFound(id)
+      case Some(entry) if entry.isOver => badRequest("GAME_OVER", "Game is already over")
+      case Some(entry)                 =>
+        val squareOpt = req.uri.query.params.get("square").flatMap(Square.fromAlgebraic)
+        IO.blocking {
+          val ctx = entry.engine.context
+          val rs  = entry.engine.ruleSet
+          squareOpt.map(rs.legalMoves(ctx)).getOrElse(rs.allLegalMoves(ctx))
+        }.flatMap { moves =>
+          Ok(LegalMovesDto(moves.map(toLegalMoveDto)).asJson)
+        }
+    }
+
+  private def undoMove(id: String): IO[Response[IO]] =
+    registry.get(id).flatMap {
+      case None                                    => notFound(id)
+      case Some(entry) if !entry.engine.canUndo    => badRequest("UNDO_UNAVAILABLE", "No moves to undo")
+      case Some(entry)                             =>
+        IO.blocking { entry.engine.undo() }.flatMap(_ => Ok(toGameStateDto(entry).asJson))
+    }
+
+  private def redoMove(id: String): IO[Response[IO]] =
+    registry.get(id).flatMap {
+      case None                                    => notFound(id)
+      case Some(entry) if !entry.engine.canRedo    => badRequest("REDO_UNAVAILABLE", "No moves to redo")
+      case Some(entry)                             =>
+        IO.blocking { entry.engine.redo() }.flatMap(_ => Ok(toGameStateDto(entry).asJson))
+    }
+
+  // ─── Draw handling ─────────────────────────────────────────────────────────
+
+  private def drawAction(id: String, action: String): IO[Response[IO]] =
+    registry.get(id).flatMap {
+      case None                        => notFound(id)
+      case Some(entry) if entry.isOver => badRequest("GAME_OVER", "Game is already over")
+      case Some(entry)                 => action match
+        case "offer"   =>
+          IO.blocking { entry.drawOffered = true }.flatMap(_ => Ok(OkDto().asJson))
+        case "decline" =>
+          IO.blocking { entry.drawOffered = false }.flatMap(_ => Ok(OkDto().asJson))
+        case "accept"  =>
+          if !entry.drawOffered then badRequest("NO_DRAW_OFFER", "No draw offer to accept")
+          else IO.blocking {
+            entry.gameOver = Some(GameOverState.Draw(entry.engine.context))
+          }.flatMap(_ => Ok(OkDto().asJson))
+        case "claim"   =>
+          IO.blocking {
+            entry.lastEvent = None
+            entry.engine.processUserInput("draw")
+            entry.lastEvent
+          }.flatMap {
+            case Some(InvalidMoveEvent(_, reason)) => badRequest("DRAW_UNAVAILABLE", reason)
+            case _                                 => Ok(OkDto().asJson)
+          }
+        case _         => badRequest("INVALID_ACTION", s"Unknown draw action: $action")
+    }
+
+  // ─── Import / Export ───────────────────────────────────────────────────────
+
+  private def importFen(req: Request[IO]): IO[Response[IO]] =
+    req.as[ImportFenRequest].flatMap { body =>
+      FenParser.parseFen(body.fen) match
+        case Left(err)  => badRequest("INVALID_FEN", err)
+        case Right(ctx) =>
+          val white = resolvePlayer(body.white, "white")
+          val black = resolvePlayer(body.black, "black")
+          val entry = GameEntry(new GameEngine(ctx), white, black)
+          registry.add(entry).flatMap { id => Created(toGameFullDto(id, entry).asJson) }
+    }
+
+  private def importPgn(req: Request[IO]): IO[Response[IO]] =
+    req.as[ImportPgnRequest].flatMap { body =>
+      val engine = new GameEngine()
+      engine.loadGame(PgnParser, body.pgn) match
+        case Left(err) => badRequest("INVALID_PGN", err)
+        case Right(_)  =>
+          val entry = GameEntry(engine, defaultPlayer("white"), defaultPlayer("black"))
+          registry.add(entry).flatMap { id => Created(toGameFullDto(id, entry).asJson) }
+    }
+
+  private def exportFen(id: String): IO[Response[IO]] =
+    registry.get(id).flatMap {
+      case None        => notFound(id)
+      case Some(entry) => Ok(FenExporter.gameContextToFen(entry.activeContext))
+    }
+
+  private def exportPgn(id: String): IO[Response[IO]] =
+    registry.get(id).flatMap {
+      case None        => notFound(id)
+      case Some(entry) => Ok(PgnExporter.exportGameContext(entry.activeContext))
+    }
+
+  // ─── Mapping helpers ───────────────────────────────────────────────────────
+
+  private def toGameStateDto(entry: GameEntry): GameStateDto =
+    val ctx = entry.activeContext
+    val (status, winner) = computeStatus(entry)
+    GameStateDto(
+      fen           = FenExporter.gameContextToFen(ctx),
+      pgn           = PgnExporter.exportGameContext(ctx),
+      turn          = ctx.turn.toString.toLowerCase,
+      status        = status,
+      winner        = winner,
+      moves         = ctx.moves.map(moveToUci),
+      undoAvailable = entry.engine.canUndo,
+      redoAvailable = entry.engine.canRedo
+    )
+
+  private def toGameFullDto(id: String, entry: GameEntry): GameFullDto =
+    GameFullDto(
+      gameId = id,
+      white  = PlayerInfoDto(entry.white.id.value, entry.white.displayName),
+      black  = PlayerInfoDto(entry.black.id.value, entry.black.displayName),
+      state  = toGameStateDto(entry)
+    )
+
+  private def toLegalMoveDto(move: Move): LegalMoveDto =
+    val (moveType, promo) = move.moveType match
+      case MoveType.Normal(true)   => ("capture", None)
+      case MoveType.Normal(false)  => ("normal", None)
+      case MoveType.CastleKingside => ("castleKingside", None)
+      case MoveType.CastleQueenside => ("castleQueenside", None)
+      case MoveType.EnPassant      => ("enPassant", None)
+      case MoveType.Promotion(pp)  =>
+        val s = pp match
+          case PromotionPiece.Queen  => "queen"
+          case PromotionPiece.Rook   => "rook"
+          case PromotionPiece.Bishop => "bishop"
+          case PromotionPiece.Knight => "knight"
+        ("promotion", Some(s))
+    LegalMoveDto(move.from.toString, move.to.toString, moveToUci(move), moveType, promo)
+
+  private def moveToUci(move: Move): String =
+    val base = s"${move.from}${move.to}"
+    move.moveType match
+      case MoveType.Promotion(pp) =>
+        val char = pp match
+          case PromotionPiece.Queen  => "q"
+          case PromotionPiece.Rook   => "r"
+          case PromotionPiece.Bishop => "b"
+          case PromotionPiece.Knight => "n"
+        base + char
+      case _ => base
+
+  private def applyUci(entry: GameEntry, uci: String): Unit =
+    if uci.length == 5 then
+      entry.engine.processUserInput(uci.take(4))
+      if entry.engine.isPendingPromotion then
+        val pp = uci.last match
+          case 'q' => PromotionPiece.Queen
+          case 'r' => PromotionPiece.Rook
+          case 'b' => PromotionPiece.Bishop
+          case _   => PromotionPiece.Knight
+        entry.engine.completePromotion(pp)
+    else
+      entry.engine.processUserInput(uci)
+
+  private def computeStatus(entry: GameEntry): (String, Option[String]) =
+    entry.gameOver match
+      case Some(GameOverState.Checkmate(w, _)) => ("checkmate", Some(w.toString.toLowerCase))
+      case Some(GameOverState.Stalemate(_))    => ("stalemate", None)
+      case Some(GameOverState.Draw(_))         => ("draw", None)
+      case Some(GameOverState.Resigned(w, _))  => ("resign", Some(w.toString.toLowerCase))
+      case None                                => statusFromContext(entry)
+
+  private def statusFromContext(entry: GameEntry): (String, Option[String]) =
+    if entry.engine.isPendingPromotion then ("promotionPending", None)
+    else if entry.drawOffered          then ("drawOffered", None)
+    else
+      val ctx = entry.engine.context
+      val rs  = entry.engine.ruleSet
+      if rs.isInsufficientMaterial(ctx) then ("insufficientMaterial", None)
+      else if rs.isFiftyMoveRule(ctx)   then ("fiftyMoveAvailable", None)
+      else if rs.isCheck(ctx)           then ("check", None)
+      else ("started", None)
+
+  // ─── Utility ───────────────────────────────────────────────────────────────
+
+  private def resolvePlayer(dto: Option[PlayerInfoDto], color: String): PlayerInfo =
+    dto.map(d => PlayerInfo(PlayerId(d.id), d.displayName))
+      .getOrElse(defaultPlayer(color))
+
+  private def defaultPlayer(color: String): PlayerInfo =
+    PlayerInfo(PlayerId(color), color.capitalize)
+
+  private def notFound(id: String): IO[Response[IO]] =
+    NotFound(ApiErrorDto("GAME_NOT_FOUND", s"Game not found: $id").asJson)
+
+  private def badRequest(code: String, msg: String): IO[Response[IO]] =
+    BadRequest(ApiErrorDto(code, msg).asJson)

modules/server/src/main/scala/de/nowchess/server/GameEntry.scala

@@ -0,0 +1,41 @@
+package de.nowchess.server
+
+import de.nowchess.api.board.Color
+import de.nowchess.api.game.GameContext
+import de.nowchess.api.player.PlayerInfo
+import de.nowchess.chess.engine.GameEngine
+import de.nowchess.chess.observer.*
+
+enum GameOverState:
+  case Checkmate(winner: Color, context: GameContext)
+  case Stalemate(context: GameContext)
+  case Draw(context: GameContext)
+  case Resigned(winner: Color, context: GameContext)
+
+class GameEntry(
+  val engine: GameEngine,
+  val white: PlayerInfo,
+  val black: PlayerInfo
+):
+  var lastEvent: Option[GameEvent] = None
+  var gameOver: Option[GameOverState] = None
+  var drawOffered: Boolean = false
+
+  engine.subscribe(new Observer:
+    def onGameEvent(event: GameEvent): Unit =
+      lastEvent = Some(event)
+      event match
+        case CheckmateEvent(ctx, winner) => gameOver = Some(GameOverState.Checkmate(winner, ctx))
+        case StalemateEvent(ctx)         => gameOver = Some(GameOverState.Stalemate(ctx))
+        case DrawClaimedEvent(ctx)       => gameOver = Some(GameOverState.Draw(ctx))
+        case _                           => ()
+  )
+
+  def isOver: Boolean = gameOver.isDefined
+
+  def activeContext: GameContext = gameOver match
+    case Some(GameOverState.Checkmate(_, ctx)) => ctx
+    case Some(GameOverState.Stalemate(ctx))    => ctx
+    case Some(GameOverState.Draw(ctx))         => ctx
+    case Some(GameOverState.Resigned(_, ctx))  => ctx
+    case None                                  => engine.context

modules/server/src/main/scala/de/nowchess/server/GameRegistry.scala

@@ -0,0 +1,21 @@
+package de.nowchess.server
+
+import cats.effect.{IO, Ref}
+import de.nowchess.api.player.{PlayerId, PlayerInfo}
+import de.nowchess.chess.engine.GameEngine
+
+class GameRegistry(ref: Ref[IO, Map[String, GameEntry]]):
+
+  def create(white: PlayerInfo, black: PlayerInfo): IO[String] =
+    add(GameEntry(new GameEngine(), white, black))
+
+  def add(entry: GameEntry): IO[String] =
+    val id = scala.util.Random.alphanumeric.take(8).mkString
+    ref.update(_ + (id -> entry)).as(id)
+
+  def get(id: String): IO[Option[GameEntry]] =
+    ref.get.map(_.get(id))
+
+object GameRegistry:
+  def make: IO[GameRegistry] =
+    Ref.of[IO, Map[String, GameEntry]](Map.empty).map(new GameRegistry(_))

modules/server/src/main/scala/de/nowchess/server/JsonCodecs.scala

@@ -0,0 +1,18 @@
+package de.nowchess.server
+
+import io.circe.{Decoder, Encoder}
+import io.circe.generic.semiauto.*
+
+object JsonCodecs:
+  given Decoder[PlayerInfoDto]    = deriveDecoder
+  given Encoder[PlayerInfoDto]    = deriveEncoder
+  given Decoder[CreateGameRequest]  = deriveDecoder
+  given Decoder[ImportFenRequest]   = deriveDecoder
+  given Decoder[ImportPgnRequest]   = deriveDecoder
+  given Encoder[GameStateDto]       = deriveEncoder
+  given Encoder[GameFullDto]        = deriveEncoder
+  given Encoder[GameFullEvent]      = deriveEncoder
+  given Encoder[LegalMoveDto]       = deriveEncoder
+  given Encoder[LegalMovesDto]      = deriveEncoder
+  given Encoder[OkDto]              = deriveEncoder
+  given Encoder[ApiErrorDto]        = deriveEncoder

modules/server/src/main/scala/de/nowchess/server/Models.scala

@@ -0,0 +1,54 @@
+package de.nowchess.server
+
+case class PlayerInfoDto(id: String, displayName: String)
+
+case class CreateGameRequest(
+  white: Option[PlayerInfoDto] = None,
+  black: Option[PlayerInfoDto] = None
+)
+
+case class ImportFenRequest(
+  fen: String,
+  white: Option[PlayerInfoDto] = None,
+  black: Option[PlayerInfoDto] = None
+)
+
+case class ImportPgnRequest(pgn: String)
+
+case class GameStateDto(
+  fen: String,
+  pgn: String,
+  turn: String,
+  status: String,
+  winner: Option[String],
+  moves: List[String],
+  undoAvailable: Boolean,
+  redoAvailable: Boolean
+)
+
+case class GameFullDto(
+  gameId: String,
+  white: PlayerInfoDto,
+  black: PlayerInfoDto,
+  state: GameStateDto
+)
+
+case class GameFullEvent(`type`: String, game: GameFullDto)
+
+case class LegalMoveDto(
+  from: String,
+  to: String,
+  uci: String,
+  moveType: String,
+  promotion: Option[String]
+)
+
+case class LegalMovesDto(moves: List[LegalMoveDto])
+
+case class OkDto(ok: Boolean = true)
+
+case class ApiErrorDto(
+  code: String,
+  message: String,
+  field: Option[String] = None
+)

modules/server/src/main/scala/de/nowchess/server/ServerApp.scala

@@ -0,0 +1,17 @@
+package de.nowchess.server
+
+import cats.effect.{ExitCode, IO, IOApp}
+import com.comcast.ip4s.{host, port}
+import org.http4s.ember.server.EmberServerBuilder
+
+object ServerApp extends IOApp:
+  def run(args: List[String]): IO[ExitCode] =
+    GameRegistry.make.flatMap { registry =>
+      EmberServerBuilder
+        .default[IO]
+        .withHost(host"0.0.0.0")
+        .withPort(port"8080")
+        .withHttpApp(BoardRoutes(registry).routes.orNotFound)
+        .build
+        .useForever
+    }.as(ExitCode.Success)

modules/server/src/main/scala/de/nowchess/server/ServerLauncher.scala

@@ -0,0 +1,25 @@
+package de.nowchess.server
+
+import cats.effect.IO
+import cats.effect.unsafe.implicits.global
+import com.comcast.ip4s.{host, port}
+import de.nowchess.api.player.{PlayerId, PlayerInfo}
+import de.nowchess.chess.engine.GameEngine
+import org.http4s.ember.server.EmberServerBuilder
+
+object ServerLauncher:
+  def start(engine: GameEngine): String =
+    val white = PlayerInfo(PlayerId("white"), "Player 1")
+    val black = PlayerInfo(PlayerId("black"), "Player 2")
+    (for
+      registry <- GameRegistry.make
+      _        <- EmberServerBuilder
+                    .default[IO]
+                    .withHost(host"0.0.0.0")
+                    .withPort(port"8080")
+                    .withHttpApp(BoardRoutes(registry).routes.orNotFound)
+                    .build
+                    .useForever
+                    .start
+      gameId   <- registry.add(GameEntry(engine, white, black))
+    yield gameId).unsafeRunSync()

modules/ui/build.gradle.kts

@@ -64,6 +64,7 @@ dependencies {
     implementation(project(":modules:rule"))
     implementation(project(":modules:api"))
     implementation(project(":modules:io"))
+    implementation(project(":modules:server"))
 
     // ScalaFX dependencies
     implementation("org.scalafx:scalafx_3:${versions["SCALAFX"]!!}")

modules/ui/src/main/scala/de/nowchess/ui/Main.scala

@@ -1,21 +1,22 @@
 package de.nowchess.ui
 
 import de.nowchess.chess.engine.GameEngine
+import de.nowchess.server.ServerLauncher
 import de.nowchess.ui.terminal.TerminalUI
 import de.nowchess.ui.gui.ChessGUILauncher
 
 /** Application entry point - starts both GUI and Terminal UI for the chess game.
  *  Both views subscribe to the same GameEngine via Observer pattern.
+ *  The REST server shares the same engine instance, so API moves are reflected in the UI.
  */
 object Main:
   def main(args: Array[String]): Unit =
-    // Create the core game engine (single source of truth)
     val engine = new GameEngine()
+    val gameId = ServerLauncher.start(engine)
+    println(s"REST API ready — game ID: $gameId  →  http://localhost:8080/api/board/game/$gameId")
 
-    // Launch ScalaFX GUI in separate thread
     ChessGUILauncher.launch(engine)
 
-    // Create and start the terminal UI (blocks on main thread)
     val tui = new TerminalUI(engine)
     tui.start()
 

settings.gradle.kts

@@ -5,4 +5,5 @@ include(
     "modules:io",
     "modules:rule",
     "modules:ui",
+    "modules:server",
 )