add prohibited move checks

backend/src/main/java/djmil/cordacheckers/cordaclient/CordaClient.java

@@ -18,7 +18,7 @@ import com.fasterxml.jackson.databind.ObjectMapper;
 
 import djmil.cordacheckers.cordaclient.dao.GameState;
 import djmil.cordacheckers.cordaclient.dao.HoldingIdentity;
-import djmil.cordacheckers.cordaclient.dao.Piece;
+import djmil.cordacheckers.cordaclient.dao.Stone;
 import djmil.cordacheckers.cordaclient.dao.Rank;
 import djmil.cordacheckers.cordaclient.dao.VirtualNode;
 import djmil.cordacheckers.cordaclient.dao.VirtualNodeList;
@@ -95,7 +95,7 @@ public class CordaClient {
             .getResponce(requestBody);
     }
 
-    public GameState gameProposalCreate(HoldingIdentity issuer, HoldingIdentity acquier, Piece.Color acquierColor,
+    public GameState gameProposalCreate(HoldingIdentity issuer, HoldingIdentity acquier, Stone.Color acquierColor,
             String message
     ) {
         final RequestBody requestBody = new RequestBody(

backend/src/main/java/djmil/cordacheckers/cordaclient/dao/GameState.java

@@ -7,9 +7,9 @@ import java.util.UUID;
 public record GameState(
     Status status,
     String opponentName,
-    Piece.Color opponentColor,
+    Stone.Color opponentColor,
     
-    Map<Integer, Piece> board,
+    Map<Integer, Stone> board,
     Integer moveNumber,
     List<Integer> previousMove,
 

backend/src/main/java/djmil/cordacheckers/cordaclient/dao/Stone.java

@@ -1,6 +1,6 @@
 package djmil.cordacheckers.cordaclient.dao;
 
-public class Piece {
+public class Stone {
     
     public enum Type {
         MAN,
@@ -19,12 +19,12 @@ public class Piece {
     Color color;
     Type type;
 
-    public Piece() {
+    public Stone() {
         this.color = null;
         this.type = null;
     }
 
-    public Piece(Color color, Type type) {
+    public Stone(Color color, Type type) {
         this.color = color;
         this.type = type;
     }
@@ -50,7 +50,7 @@ public class Piece {
             return false;
         if (getClass() != obj.getClass())
             return false;
-        Piece other = (Piece) obj;
+        Stone other = (Stone) obj;
         if (color != other.color)
             return false;
         if (type != other.type)

backend/src/main/java/djmil/cordacheckers/cordaclient/dao/flow/arguments/ReqGameProposalCreate.java

@@ -1,10 +1,10 @@
 package djmil.cordacheckers.cordaclient.dao.flow.arguments;
 
-import djmil.cordacheckers.cordaclient.dao.Piece;
+import djmil.cordacheckers.cordaclient.dao.Stone;
 
 public record ReqGameProposalCreate(
     String opponentName,
-    Piece.Color opponentColor,
+    Stone.Color opponentColor,
     String message
 ) {
     

backend/src/main/java/djmil/cordacheckers/gameproposal/GameProposalController.java

@@ -19,7 +19,7 @@ import com.fasterxml.jackson.databind.JsonMappingException;
 import djmil.cordacheckers.cordaclient.CordaClient;
 import djmil.cordacheckers.cordaclient.dao.GameState;
 import djmil.cordacheckers.cordaclient.dao.HoldingIdentity;
-import djmil.cordacheckers.cordaclient.dao.Piece;
+import djmil.cordacheckers.cordaclient.dao.Stone;
 import djmil.cordacheckers.cordaclient.dao.flow.arguments.ReqGameProposalCreate;
 import djmil.cordacheckers.user.HoldingIdentityResolver;
 import djmil.cordacheckers.user.User;
@@ -59,7 +59,7 @@ public class GameProposalController {
         final HoldingIdentity gpSender = sender.getHoldingIdentity();
         // TODO: throw execption with custom type
         final HoldingIdentity gpReceiver = holdingIdentityResolver.getByUsername(gpRequest.opponentName());
-        final Piece.Color gpReceiverColor = gpRequest.opponentColor();
+        final Stone.Color gpReceiverColor = gpRequest.opponentColor();
 
         // TODO handle expectionns here
         GameState gameStateView = cordaClient.gameProposalCreate(

backend/src/test/java/djmil/cordacheckers/CheckersMoveTest.java

@@ -0,0 +1,215 @@
+package djmil.cordacheckers;
+
+import static java.lang.Math.abs;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import org.junit.jupiter.api.Test;
+import org.junit.platform.commons.annotation.Testable;
+
+@Testable
+public class CheckersMoveTest {
+
+    public final static Map<Integer, List<Integer>> adjacentCell = Map.ofEntries(
+        Map.entry(1, Arrays.asList(5, 6, 10)),
+        Map.entry(2, Arrays.asList(6, 7, 9, 11)),
+        Map.entry(3, Arrays.asList(7, 8, 10, 12)),
+        Map.entry(4, Arrays.asList(8, 11)),
+        Map.entry(5, Arrays.asList(1, 9, 14, 9, 11)),
+        Map.entry(6, Arrays.asList(1, 2, 9, 10, 13, 15)),
+        Map.entry(7, Arrays.asList(2, 3, 10, 11, 14, 16)),
+        Map.entry(8, Arrays.asList(3, 4, 11, 12, 15)),
+        Map.entry(9, Arrays.asList(2, 5, 6, 13, 14, 18)),
+        Map.entry(10, Arrays.asList(1, 3, 6, 7, 14, 15, 17, 19)),
+        Map.entry(11, Arrays.asList(2, 4, 7, 8, 15, 16, 18, 20)),
+        Map.entry(12, Arrays.asList(3, 8, 16, 19)),
+        Map.entry(13, Arrays.asList(6, 9, 17, 22)),
+        Map.entry(14, Arrays.asList(5, 7, 9, 10, 17, 18, 21, 23)),
+        Map.entry(15, Arrays.asList(6, 8, 10, 11, 18, 19, 22, 24)),
+        Map.entry(16, Arrays.asList(7, 11, 12, 19, 20, 23)),
+        Map.entry(17, Arrays.asList(10, 13, 14, 21, 22, 26)),
+        Map.entry(18, Arrays.asList(9, 11, 14, 15, 22, 23, 25, 27)),
+        Map.entry(19, Arrays.asList(10, 12, 15, 16, 23, 24)),
+        Map.entry(20, Arrays.asList(11, 16, 24, 27)),
+        Map.entry(21, Arrays.asList(14, 17, 25, 30)),
+        Map.entry(22, Arrays.asList(13, 15, 17, 18, 25, 26, 29, 31)),
+        Map.entry(23, Arrays.asList(14, 16, 18, 19, 26, 27, 30, 32)),
+        Map.entry(24, Arrays.asList(15, 19, 20, 27, 28, 31)),
+        Map.entry(25, Arrays.asList(18, 21, 22, 29, 30)),
+        Map.entry(26, Arrays.asList(17, 19, 22, 23, 30, 31)),
+        Map.entry(27, Arrays.asList(18, 20, 23, 24, 31, 32)),
+        Map.entry(28, Arrays.asList(19, 24, 32)),
+        Map.entry(29, Arrays.asList(22, 25)),
+        Map.entry(30, Arrays.asList(21, 23, 25, 26)),
+        Map.entry(31, Arrays.asList(22, 24, 26, 27)),
+        Map.entry(32, Arrays.asList(23, 27, 28))
+    );
+
+    public static class Jump {
+        final public int jump;
+        final public int step;
+        Jump(int jump, int step) {
+            this.jump = jump;
+            this.step = step;
+        }
+
+        static Set<Jump> intersect(Set<Integer> jumps, Set<Integer> steps) {
+            Set<Jump> res = new HashSet<Jump>();
+            for (Integer jump :jumps) {
+                var jumpSteps = getKingSteps(jump);
+                jumpSteps.retainAll(steps);
+
+                if (jumpSteps.size() == 1)
+                    res.add(new Jump(jump, jumpSteps.iterator().next()));
+            }
+            return res;
+        }
+
+        @Override
+        public String toString() {
+            return "[jump=" + jump + ", step=" + step + "]";
+        }
+        @Override
+        public int hashCode() {
+            final int prime = 31;
+            int result = 1;
+            result = prime * result + jump;
+            result = prime * result + step;
+            return result;
+        }
+        @Override
+        public boolean equals(Object obj) {
+            if (this == obj)
+                return true;
+            if (obj == null)
+                return false;
+            if (getClass() != obj.getClass())
+                return false;
+            Jump other = (Jump) obj;
+            if (jump != other.jump)
+                return false;
+            if (step != other.step)
+                return false;
+            return true;
+        }
+        
+    }
+
+    public static Set<Integer> getBlackSteps(Integer idx) {
+        return adjacentCell.get(idx).stream()
+            .filter(cur -> cur > idx && cur - idx <= 5)
+            .collect(Collectors.toSet());
+    }
+
+    public static Set<Integer> getWhiteSteps(Integer idx) {
+        return adjacentCell.get(idx).stream()
+            .filter(cur -> cur < idx && idx - cur <= 5)
+            .collect(Collectors.toSet());
+    }
+
+    public static Set<Integer> getKingSteps(Integer idx) {
+        return adjacentCell.get(idx).stream()
+            .filter(cur -> abs(idx - cur) <= 5)
+            .collect(Collectors.toSet());
+    }
+
+    public static Set<Jump> getBlackJumps(Integer idx) {
+        final var allSteps = getBlackSteps(idx);
+        final var allJumps = adjacentCell.get(idx).stream()
+            .filter(cur -> cur > idx && cur - idx > 5)
+            .collect(Collectors.toSet());
+
+        return Jump.intersect(allJumps, allSteps);
+    }
+
+    public static Set<Jump> getWhiteJumps(Integer idx) {
+        final var allSteps = getWhiteSteps(idx);
+        final var allJumps = adjacentCell.get(idx).stream()
+            .filter(cur -> idx > cur && idx - cur > 5)
+            .collect(Collectors.toSet());
+
+        return Jump.intersect(allJumps, allSteps);
+    }
+
+    public static Set<Jump> getKingJumps(Integer idx) {
+        final var allSteps = getKingSteps(idx);
+        final var allJumps = adjacentCell.get(idx).stream()
+            .filter(cur -> abs(idx - cur) > 5)
+            .collect(Collectors.toSet());
+
+        return Jump.intersect(allJumps, allSteps);
+    }
+
+    @Test
+    void blackStepTest() {
+        assertThat(getBlackSteps(1)).containsAll(Arrays.asList(5, 6));
+        assertThat(getBlackSteps(4)).containsAll(Arrays.asList(8));
+        assertThat(getBlackSteps(18)).containsAll(Arrays.asList(22, 23));
+        assertThat(getBlackSteps(21)).containsAll(Arrays.asList(25));
+    }
+
+    @Test
+    void whiteStepTest() {
+        assertThat(getWhiteSteps(29)).containsAll(Arrays.asList(25));
+        assertThat(getWhiteSteps(28)).containsAll(Arrays.asList(24));
+        assertThat(getWhiteSteps(14)).containsAll(Arrays.asList(9, 10));
+        assertThat(getWhiteSteps(8)).containsAll(Arrays.asList(3, 4));
+    }
+
+    @Test
+    void kingStepTest() {
+        assertThat(getKingSteps(29)).containsAll(Arrays.asList(25));
+        assertThat(getKingSteps(31)).containsAll(Arrays.asList(26, 27));
+        assertThat(getKingSteps(20)).containsAll(Arrays.asList(16, 24));
+        assertThat(getKingSteps(13)).containsAll(Arrays.asList(9, 17));
+        assertThat(getKingSteps(2)).containsAll(Arrays.asList(6, 7));
+        assertThat(getKingSteps(15)).containsAll(Arrays.asList(10, 11, 18, 19));
+    }
+
+    @Test
+    void blackJumpTest() {
+        assertThat(getBlackJumps(4)).containsAll(
+            Arrays.asList(new Jump(11, 8)));
+
+        assertThat(getBlackJumps(16)).containsAll(
+            Arrays.asList(new Jump(23, 19)));
+
+        assertThat(getBlackJumps(15)).containsAll(
+            Arrays.asList(new Jump(22, 18), new Jump(24, 19)));
+
+        assertThat(getBlackJumps(28)).isEmpty();
+    }
+
+    @Test
+    void whiteJumpTest() {
+        assertThat(getWhiteJumps(30)).containsAll(
+            Arrays.asList(new Jump(21, 25), new Jump(23, 26)));
+
+        assertThat(getWhiteJumps(17)).containsAll(
+            Arrays.asList(new Jump(10, 14)));
+
+        assertThat(getWhiteJumps(7)).isEmpty();
+
+        assertThat(getWhiteJumps(9)).containsAll(
+            Arrays.asList(new Jump(2, 6)));
+    }
+
+    @Test
+    void kingJumpTest() {
+        assertThat(getKingJumps(11)).containsAll(
+            Arrays.asList(new Jump(2, 7), new Jump(4, 8), new Jump(18, 15),new Jump(20, 16)));
+       
+        assertThat(getKingJumps(17)).containsAll(
+            Arrays.asList(new Jump(10, 14), new Jump(26, 22)));
+
+        assertThat(getKingJumps(32)).containsAll(
+            Arrays.asList(new Jump(23, 27)));
+    }
+
+}

backend/src/test/java/djmil/cordacheckers/cordaclient/GameBoardTests.java

@@ -12,7 +12,7 @@ import org.springframework.boot.test.context.SpringBootTest;
 
 import djmil.cordacheckers.cordaclient.dao.GameState;
 import djmil.cordacheckers.cordaclient.dao.GameState.Status;
-import djmil.cordacheckers.cordaclient.dao.Piece;
+import djmil.cordacheckers.cordaclient.dao.Stone;
 import djmil.cordacheckers.user.HoldingIdentityResolver;
 
 @SpringBootTest
@@ -26,10 +26,10 @@ public class GameBoardTests {
     final String whitePlayerName = "alice";
     final String blackPlayerName = "bob";
 
-    final static Piece WHITE_MAN  = new Piece(Piece.Color.WHITE, Piece.Type.MAN);
-    final static Piece WHITE_KING = new Piece(Piece.Color.WHITE, Piece.Type.KING);
-    final static Piece BLACK_MAN  = new Piece(Piece.Color.BLACK, Piece.Type.MAN);
-    final static Piece BLACK_KING = new Piece(Piece.Color.BLACK, Piece.Type.KING);
+    final static Stone WHITE_MAN  = new Stone(Stone.Color.WHITE, Stone.Type.MAN);
+    final static Stone WHITE_KING = new Stone(Stone.Color.WHITE, Stone.Type.KING);
+    final static Stone BLACK_MAN  = new Stone(Stone.Color.BLACK, Stone.Type.MAN);
+    final static Stone BLACK_KING = new Stone(Stone.Color.BLACK, Stone.Type.KING);
 
     @Test
     void testSurrender() {
@@ -38,14 +38,14 @@ public class GameBoardTests {
         final String message = "GameBoard SURRENDER test";
 
         final GameState game = cordaClient.gameProposalCreate(
-            hiWhite, hiBlack, Piece.Color.BLACK, message);
+            hiWhite, hiBlack, Stone.Color.BLACK, message);
 
         System.out.println("Game UUID " +game.uuid());
 
         final GameState acceptedGameBlackView = cordaClient.gameProposalAccept(
             hiBlack, game.uuid());
 
-        assertThat(acceptedGameBlackView.opponentColor()).isEqualByComparingTo(Piece.Color.WHITE);
+        assertThat(acceptedGameBlackView.opponentColor()).isEqualByComparingTo(Stone.Color.WHITE);
         assertThat(acceptedGameBlackView.status()).isEqualByComparingTo(Status.GAME_BOARD_WAIT_FOR_OPPONENT);
 
         assertThatThrownBy(() -> { // Black can not surrender, since it is opponent's turn
@@ -57,14 +57,14 @@ public class GameBoardTests {
             hiWhite, game.uuid());
 
         assertThat(surrendererGameView.opponentName()).isEqualToIgnoringCase(blackPlayerName);
-        assertThat(surrendererGameView.opponentColor()).isEqualByComparingTo(Piece.Color.BLACK);
+        assertThat(surrendererGameView.opponentColor()).isEqualByComparingTo(Stone.Color.BLACK);
         assertThat(surrendererGameView.status()).isEqualByComparingTo(Status.GAME_RESULT_YOU_LOOSE);
 
         final GameState winnerGameView = cordaClient.gameStateGet(
             hiBlack, game.uuid());
 
         assertThat(winnerGameView.opponentName()).isEqualToIgnoringCase(whitePlayerName);
-        assertThat(winnerGameView.opponentColor()).isEqualByComparingTo(Piece.Color.WHITE);
+        assertThat(winnerGameView.opponentColor()).isEqualByComparingTo(Stone.Color.WHITE);
         assertThat(winnerGameView.status()).isEqualByComparingTo(Status.GAME_RESULT_YOU_WON);
     }
 
@@ -75,7 +75,7 @@ public class GameBoardTests {
         final String message = "GameBoard MOVE test";
 
         final GameState game = cordaClient.gameProposalCreate(
-            hiWhite, hiBlack, Piece.Color.BLACK, message);
+            hiWhite, hiBlack, Stone.Color.BLACK, message);
         System.out.println("Game UUID " +game.uuid());
 
         final var m0 = cordaClient.gameProposalAccept(hiBlack, game.uuid());
@@ -95,7 +95,21 @@ public class GameBoardTests {
         assertThat(m0.board().get(18)).isNull();
         assertThat(m1.board().get(22)).isNull();
         assertThat(m1.board().get(18)).isEqualTo(WHITE_MAN);
+        assertThat(m1.moveNumber() == 1);
         assertThat(m1.status()).isEqualByComparingTo(Status.GAME_BOARD_WAIT_FOR_OPPONENT);
+
+        assertThatThrownBy(() -> { 
+            cordaClient.gameBoardMove(hiBlack, game.uuid(), move(12, 13), 
+            "Prohibitted move shall be rejected");
+        });
+
+        final var m2 = cordaClient.gameBoardMove(hiBlack, game.uuid(), move(11, 15), null);
+        assertThat(m1.board().get(11)).isEqualTo(BLACK_MAN);
+        assertThat(m1.board().get(15)).isNull();
+        assertThat(m2.board().get(11)).isNull();
+        assertThat(m2.board().get(15)).isEqualTo(BLACK_MAN);
+        assertThat(m2.moveNumber() == 2);
+        assertThat(m2.status()).isEqualByComparingTo(Status.GAME_BOARD_WAIT_FOR_OPPONENT);
     }
 
     ArrayList<Integer> move(int from, int to) {

backend/src/test/java/djmil/cordacheckers/cordaclient/GameProposalTests.java

@@ -10,7 +10,7 @@ import org.springframework.boot.test.context.SpringBootTest;
 
 import djmil.cordacheckers.cordaclient.dao.GameState;
 import djmil.cordacheckers.cordaclient.dao.GameState.Status;
-import djmil.cordacheckers.cordaclient.dao.Piece;
+import djmil.cordacheckers.cordaclient.dao.Stone;
 import djmil.cordacheckers.user.HoldingIdentityResolver;
 
 @SpringBootTest
@@ -23,7 +23,7 @@ public class GameProposalTests {
 
     final String issuer = "alice";
     final String acquier = "bob";
-    final Piece.Color acquierColor = Piece.Color.WHITE;
+    final Stone.Color acquierColor = Stone.Color.WHITE;
 
     @Test
     void testCreate() {

backend/src/test/java/djmil/cordacheckers/cordaclient/GameStateTests.java

@@ -8,7 +8,7 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
 
 import djmil.cordacheckers.cordaclient.dao.GameState;
-import djmil.cordacheckers.cordaclient.dao.Piece;
+import djmil.cordacheckers.cordaclient.dao.Stone;
 import djmil.cordacheckers.user.HoldingIdentityResolver;
 
 @SpringBootTest
@@ -21,7 +21,7 @@ public class GameStateTests {
 
     final String issuer = "alice";
     final String acquier = "bob";
-    final Piece.Color acquierColor = Piece.Color.WHITE;
+    final Stone.Color acquierColor = Stone.Color.WHITE;
 
     @Test
     void testList() {

backend/src/test/java/djmil/cordacheckers/cordaclient/RankingTests.java

@@ -9,7 +9,7 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
 
 import djmil.cordacheckers.cordaclient.dao.GameState;
-import djmil.cordacheckers.cordaclient.dao.Piece;
+import djmil.cordacheckers.cordaclient.dao.Stone;
 import djmil.cordacheckers.cordaclient.dao.Rank;
 import djmil.cordacheckers.user.HoldingIdentityResolver;
 
@@ -32,7 +32,7 @@ public class RankingTests {
         final var hiLooser = holdingIdentityResolver.getByUsername("Bob");
 
         final GameState game = cordaClient.gameProposalCreate(
-            hiWinner, hiLooser, Piece.Color.WHITE, "GameBoard GLOBAL_RANKING test");
+            hiWinner, hiLooser, Stone.Color.WHITE, "GameBoard GLOBAL_RANKING test");
 
         cordaClient.gameProposalAccept(hiLooser, game.uuid());
         cordaClient.gameBoardSurrender(hiLooser, game.uuid());

corda/contracts/src/main/java/djmil/cordacheckers/checkers/Move.java

@@ -0,0 +1,194 @@
+package djmil.cordacheckers.checkers;
+
+import static java.lang.Math.abs;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+public class Move {
+    final public Integer from;
+    final public Integer to;
+    final public Integer jumpOver;
+
+    public Move(int from, int to) {
+        this.from = from;
+        this.to = to;
+
+        Set<Integer> fromSteps = getSteps(from);
+        if (fromSteps.contains(to))
+            this.jumpOver = null;
+        else
+            this.jumpOver = intersection(fromSteps, getSteps(to));
+    }
+
+    public static Stone.Color apply(List<Integer> moves, Map<Integer, Stone> board, Stone.Color moveColor) {
+        Move move = new Move(moves.get(0), moves.get(1));
+        return move.apply(board, moveColor);
+    }
+
+    private Stone.Color apply(Map<Integer, Stone> board, Stone.Color expectedMoveColor) {
+        Stone movingStone = board.remove(from);
+        if (movingStone == null)
+            throw new Exception("An empty starting tile");
+
+        if (movingStone.getColor() != expectedMoveColor)
+            throw new Exception("Only " +expectedMoveColor.name() +" color is expected to move");
+
+        final Set<Move> allMoves = movingStone.getMoves(from);
+        if (!allMoves.contains(this))
+            throw new Exception("Prohibited move");
+
+        // TODO: check for mandatory captures
+
+        movingStone = movingStone.promoteIfPossible(to);
+        if (board.put(to, movingStone) != null)
+            throw new Exception("An occupied finishing tile");
+
+        if (isJump()) {
+            final Stone jumpOver = board.remove(this.jumpOver);
+            if (jumpOver == null || jumpOver.getColor() != expectedMoveColor.opposite())
+                throw new Exception("Must jump over an opponent's stone");
+        }
+
+        return expectedMoveColor.opposite();
+    }
+
+    public boolean isJump() {
+        return this.jumpOver != null;
+    }
+
+    static Integer intersection(Set<Integer> a, Set<Integer> b) {
+        Set<Integer> intersection = new HashSet<Integer>(a);
+
+        intersection.retainAll(b);
+        if (intersection.size() != 1)
+            // A legit move is characterized by single intersection point
+            throw new Exception("Prohibited move");
+        
+        return intersection.iterator().next();
+    }
+
+    static Set<Integer> getSteps(Integer idx) {
+        return adjacentCell.get(idx).stream()
+            .filter(cur -> abs(idx - cur) <= 5)
+            .collect(Collectors.toSet());
+    }
+
+    static Set<Integer> getJumps(Integer idx) {
+        return adjacentCell.get(idx).stream()
+            .filter(cur -> abs(idx - cur) > 5)
+            .collect(Collectors.toSet());
+    }
+
+    static Set<Integer> getBlackSteps(Integer idx) {
+        return adjacentCell.get(idx).stream()
+            .filter(cur -> cur > idx && cur - idx <= 5)
+            .collect(Collectors.toSet());
+    }
+
+    static Set<Integer> getWhiteSteps(Integer idx) {
+        return adjacentCell.get(idx).stream()
+            .filter(cur -> cur < idx && idx - cur <= 5)
+            .collect(Collectors.toSet());
+    }
+
+    static Set<Integer> getBlackJumps(Integer idx) {
+        return adjacentCell.get(idx).stream()
+            .filter(cur -> cur > idx && cur - idx > 5)
+            .collect(Collectors.toSet());
+    }
+
+    static Set<Integer> getWhiteJumps(Integer idx) {
+        return adjacentCell.get(idx).stream()
+            .filter(cur -> cur < idx && idx - cur > 5)
+            .collect(Collectors.toSet());
+    }
+
+    final static Map<Integer, List<Integer>> adjacentCell = Map.ofEntries(
+        Map.entry(1, Arrays.asList(5, 6, 10)),
+        Map.entry(2, Arrays.asList(6, 7, 9, 11)),
+        Map.entry(3, Arrays.asList(7, 8, 10, 12)),
+        Map.entry(4, Arrays.asList(8, 11)),
+        Map.entry(5, Arrays.asList(1, 9, 14, 9, 11)),
+        Map.entry(6, Arrays.asList(1, 2, 9, 10, 13, 15)),
+        Map.entry(7, Arrays.asList(2, 3, 10, 11, 14, 16)),
+        Map.entry(8, Arrays.asList(3, 4, 11, 12, 15)),
+        Map.entry(9, Arrays.asList(2, 5, 6, 13, 14, 18)),
+        Map.entry(10, Arrays.asList(1, 3, 6, 7, 14, 15, 17, 19)),
+        Map.entry(11, Arrays.asList(2, 4, 7, 8, 15, 16, 18, 20)),
+        Map.entry(12, Arrays.asList(3, 8, 16, 19)),
+        Map.entry(13, Arrays.asList(6, 9, 17, 22)),
+        Map.entry(14, Arrays.asList(5, 7, 9, 10, 17, 18, 21, 23)),
+        Map.entry(15, Arrays.asList(6, 8, 10, 11, 18, 19, 22, 24)),
+        Map.entry(16, Arrays.asList(7, 11, 12, 19, 20, 23)),
+        Map.entry(17, Arrays.asList(10, 13, 14, 21, 22, 26)),
+        Map.entry(18, Arrays.asList(9, 11, 14, 15, 22, 23, 25, 27)),
+        Map.entry(19, Arrays.asList(10, 12, 15, 16, 23, 24)),
+        Map.entry(20, Arrays.asList(11, 16, 24, 27)),
+        Map.entry(21, Arrays.asList(14, 17, 25, 30)),
+        Map.entry(22, Arrays.asList(13, 15, 17, 18, 25, 26, 29, 31)),
+        Map.entry(23, Arrays.asList(14, 16, 18, 19, 26, 27, 30, 32)),
+        Map.entry(24, Arrays.asList(15, 19, 20, 27, 28, 31)),
+        Map.entry(25, Arrays.asList(18, 21, 22, 29, 30)),
+        Map.entry(26, Arrays.asList(17, 19, 22, 23, 30, 31)),
+        Map.entry(27, Arrays.asList(18, 20, 23, 24, 31, 32)),
+        Map.entry(28, Arrays.asList(19, 24, 32)),
+        Map.entry(29, Arrays.asList(22, 25)),
+        Map.entry(30, Arrays.asList(21, 23, 25, 26)),
+        Map.entry(31, Arrays.asList(22, 24, 26, 27)),
+        Map.entry(32, Arrays.asList(23, 27, 28))
+    );
+
+    public static class Exception extends RuntimeException {
+        public Exception(String message) {
+            super(message);
+        }
+    }
+
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = 1;
+        result = prime * result + ((from == null) ? 0 : from.hashCode());
+        result = prime * result + ((to == null) ? 0 : to.hashCode());
+        result = prime * result + ((jumpOver == null) ? 0 : jumpOver.hashCode());
+        return result;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj)
+            return true;
+        if (obj == null)
+            return false;
+        if (getClass() != obj.getClass())
+            return false;
+        Move other = (Move) obj;
+        if (from == null) {
+            if (other.from != null)
+                return false;
+        } else if (!from.equals(other.from))
+            return false;
+        if (to == null) {
+            if (other.to != null)
+                return false;
+        } else if (!to.equals(other.to))
+            return false;
+        if (jumpOver == null) {
+            if (other.jumpOver != null)
+                return false;
+        } else if (!jumpOver.equals(other.jumpOver))
+            return false;
+        return true;
+    }
+
+    @Override
+    public String toString() {
+        return "[from=" + from + ", to=" + to + ", jumpOver=" + jumpOver + "]";
+    }
+
+}

corda/contracts/src/main/java/djmil/cordacheckers/checkers/Stone.java

@@ -0,0 +1,112 @@
+package djmil.cordacheckers.checkers;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import net.corda.v5.base.annotations.ConstructorForDeserialization;
+import net.corda.v5.base.annotations.CordaSerializable;
+
+@CordaSerializable
+public class Stone {
+    
+    @CordaSerializable
+    public enum Type {
+        MAN,
+        KING;
+    }
+
+    @CordaSerializable
+    public enum Color {
+        WHITE,
+        BLACK;
+
+        public Color opposite() {
+            switch (this) {
+                case WHITE:
+                    return BLACK;
+                case BLACK:
+                    return WHITE;
+            }
+            throw new RuntimeException("Unknown Color");
+        }
+    }
+
+    private final Color color;
+    private final Type type;
+
+    @ConstructorForDeserialization
+    public Stone(Color color, Type type) {
+        this.color = color;
+        this.type = type;
+    }
+
+    public Color getColor() {
+        return color;
+    }
+
+    public Type getType() {
+        return type;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj)
+            return true;
+        if (obj == null)
+            return false;
+        if (getClass() != obj.getClass())
+            return false;
+        Stone other = (Stone) obj;
+        if (color != other.color)
+            return false;
+        if (type != other.type)
+            return false;
+        return true;
+    }
+
+    public Set<Move> getJumps(Integer from) {
+        Set<Integer> jumps;
+
+        if (type == Type.KING)
+            jumps = Move.getJumps(from);
+        else if (color == Color.BLACK)
+            jumps = Move.getBlackJumps(from);
+        else
+            jumps = Move.getWhiteJumps(from);
+
+        Set<Move> res = new HashSet<>();
+
+        for (Integer jump : jumps)
+            res.add(new Move(from, jump));
+
+        return res;
+    }
+
+    public Set<Move> getMoves(Integer from) {
+        Set<Integer> steps;
+    
+        if (type == Type.KING)
+            steps = Move.getSteps(from);
+        else if (color == Color.BLACK)
+            steps = Move.getBlackSteps(from);
+        else
+            steps = Move.getWhiteSteps(from);
+
+        Set<Move> moves = getJumps(from);       // <<--- Steps + Jumps
+        
+        for (Integer step : steps) {
+            moves.add(new Move(from, step));            
+        }
+
+        return moves;
+    }
+
+    public Stone promoteIfPossible(Integer to) {
+        if ((color == Color.WHITE && to >=  1 && to <=  4) ||
+            (color == Color.BLACK && to >= 29 && to <= 32))
+            return new Stone(color, Type.KING);
+        else 
+            return this; 
+    }
+
+}

corda/contracts/src/main/java/djmil/cordacheckers/contracts/GameBoardContract.java

@@ -3,35 +3,16 @@ package djmil.cordacheckers.contracts;
 import static djmil.cordacheckers.contracts.GameCommand.requireThat;
 import static djmil.cordacheckers.contracts.UtxoLedgerTransactionUtil.getSingleCommand;
 
-import java.util.LinkedHashMap;
-import java.util.List;
 import java.util.Map;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import djmil.cordacheckers.states.Piece;
-import djmil.cordacheckers.states.Piece.Color;
+import djmil.cordacheckers.checkers.Stone;
 import net.corda.v5.ledger.utxo.transaction.UtxoLedgerTransaction;
 
 public class GameBoardContract implements net.corda.v5.ledger.utxo.Contract {
     
-    public static class MoveResult {
-        final public Map<Integer, Piece> board;
-        final public Piece.Color moveColor;
-        
-        public MoveResult(Map<Integer, Piece> board, Color moveColor) {
-            this.board = board;
-            this.moveColor = moveColor;
-        }
-
-        public static class Exception extends RuntimeException {
-            public Exception(String message) {
-                super(message);
-            }
-        }
-    }
-
     private final static Logger log = LoggerFactory.getLogger(GameBoardContract.class);
 
     @Override
@@ -59,60 +40,33 @@ public class GameBoardContract implements net.corda.v5.ledger.utxo.Contract {
         }
     }
 
-    public static MoveResult applyMove(List<Integer> move, Map<Integer, Piece> board, Piece.Color moveColor) {
-        final int mFrom = move.get(0);
-        final int mTo   = move.get(1);
-
-        final Piece piece = board.get(mFrom);
-        if (piece == null)
-            throw new MoveResult.Exception("An empty starting tile");
-
-        if (piece.getColor() != moveColor)
-            throw new MoveResult.Exception("Can not move opponent's piece");
-
-        if (board.get(mTo) != null)
-            throw new MoveResult.Exception("An occupied finishing tile");
-
-        final Map<Integer, Piece> newBoard = new LinkedHashMap<Integer, Piece>(board);
-        newBoard.remove(mFrom);
-        newBoard.put(mTo, piece);
-
-        return new GameBoardContract.MoveResult(newBoard, moveColor.opposite());
-    }
-
-    final static Piece WHITE_MAN  = new Piece(Piece.Color.WHITE, Piece.Type.MAN);
-    final static Piece WHITE_KING = new Piece(Piece.Color.WHITE, Piece.Type.KING);
-    final static Piece BLACK_MAN  = new Piece(Piece.Color.BLACK, Piece.Type.MAN);
-    final static Piece BLACK_KING = new Piece(Piece.Color.BLACK, Piece.Type.KING);
-
-    public final static Map<Integer, Piece> initialBoard =  Map.ofEntries(
+    public final static Map<Integer, Stone> initialBoard =  Map.ofEntries(
         // Inspired by Checkers notation rules: https://www.bobnewell.net/nucleus/checkers.php
-        Map.entry( 1, BLACK_MAN),
-        Map.entry( 2, BLACK_MAN),
-        Map.entry( 3, BLACK_MAN),
-        Map.entry( 4, BLACK_MAN),
-        Map.entry( 5, BLACK_MAN),
-        Map.entry( 6, BLACK_MAN),
-        Map.entry( 7, BLACK_MAN),
-        Map.entry( 8, BLACK_MAN),
-        Map.entry( 9, BLACK_MAN),
-        Map.entry(10, BLACK_MAN),
-        Map.entry(11, BLACK_MAN),
-        Map.entry(12, BLACK_MAN),
-
-        Map.entry(21, WHITE_MAN),
-        Map.entry(22, WHITE_MAN),
-        Map.entry(23, WHITE_MAN),
-        Map.entry(24, WHITE_MAN),
-        Map.entry(25, WHITE_MAN),
-        Map.entry(26, WHITE_MAN),
-        Map.entry(27, WHITE_MAN),
-        Map.entry(28, WHITE_MAN),
-        Map.entry(29, WHITE_MAN),
-        Map.entry(30, WHITE_MAN),
-        Map.entry(31, WHITE_MAN),
-        Map.entry(32, WHITE_MAN)
-        );
+        Map.entry( 1, new Stone(Stone.Color.BLACK, Stone.Type.MAN)),
+        Map.entry( 2, new Stone(Stone.Color.BLACK, Stone.Type.MAN)),
+        Map.entry( 3, new Stone(Stone.Color.BLACK, Stone.Type.MAN)),
+        Map.entry( 4, new Stone(Stone.Color.BLACK, Stone.Type.MAN)),
+        Map.entry( 5, new Stone(Stone.Color.BLACK, Stone.Type.MAN)),
+        Map.entry( 6, new Stone(Stone.Color.BLACK, Stone.Type.MAN)),
+        Map.entry( 7, new Stone(Stone.Color.BLACK, Stone.Type.MAN)),
+        Map.entry( 8, new Stone(Stone.Color.BLACK, Stone.Type.MAN)),
+        Map.entry( 9, new Stone(Stone.Color.BLACK, Stone.Type.MAN)),
+        Map.entry(10, new Stone(Stone.Color.BLACK, Stone.Type.MAN)),
+        Map.entry(11, new Stone(Stone.Color.BLACK, Stone.Type.MAN)),
+        Map.entry(12, new Stone(Stone.Color.BLACK, Stone.Type.MAN)),
 
+        Map.entry(21, new Stone(Stone.Color.WHITE, Stone.Type.MAN)),
+        Map.entry(22, new Stone(Stone.Color.WHITE, Stone.Type.MAN)),
+        Map.entry(23, new Stone(Stone.Color.WHITE, Stone.Type.MAN)),
+        Map.entry(24, new Stone(Stone.Color.WHITE, Stone.Type.MAN)),
+        Map.entry(25, new Stone(Stone.Color.WHITE, Stone.Type.MAN)),
+        Map.entry(26, new Stone(Stone.Color.WHITE, Stone.Type.MAN)),
+        Map.entry(27, new Stone(Stone.Color.WHITE, Stone.Type.MAN)),
+        Map.entry(28, new Stone(Stone.Color.WHITE, Stone.Type.MAN)),
+        Map.entry(29, new Stone(Stone.Color.WHITE, Stone.Type.MAN)),
+        Map.entry(30, new Stone(Stone.Color.WHITE, Stone.Type.MAN)),
+        Map.entry(31, new Stone(Stone.Color.WHITE, Stone.Type.MAN)),
+        Map.entry(32, new Stone(Stone.Color.WHITE, Stone.Type.MAN))
+    );
 
 }

corda/contracts/src/main/java/djmil/cordacheckers/states/GameBoardState.java

@@ -6,25 +6,25 @@ import java.util.List;
 import java.util.Map;
 import java.util.UUID;
 
+import djmil.cordacheckers.checkers.Move;
+import djmil.cordacheckers.checkers.Stone;
 import djmil.cordacheckers.contracts.GameBoardContract;
-import djmil.cordacheckers.contracts.GameBoardContract.MoveResult;
-import djmil.cordacheckers.states.Piece.Color;
 import net.corda.v5.base.annotations.ConstructorForDeserialization;
 import net.corda.v5.base.types.MemberX500Name;
 import net.corda.v5.ledger.utxo.BelongsToContract;
 
 @BelongsToContract(GameBoardContract.class)
 public class GameBoardState extends GameState {
-    private final Piece.Color moveColor;
+    private final Stone.Color moveColor;
     private final Integer moveNumber;
-    private final Map<Integer, Piece> board;
+    private final Map<Integer, Stone> board;
 
     public GameBoardState(GameProposalState gameProposalState) {
         super(gameProposalState.whitePlayer, gameProposalState.blackPlayer, 
             gameProposalState.gameUuid, gameProposalState.message, gameProposalState.participants);
         
-        this.board = new LinkedHashMap<Integer, Piece>(GameBoardContract.initialBoard);
-        this.moveColor = Piece.Color.WHITE;
+        this.board = new LinkedHashMap<Integer, Stone>(GameBoardContract.initialBoard);
+        this.moveColor = Stone.Color.WHITE;
         this.moveNumber = 0;
     }
 
@@ -32,9 +32,8 @@ public class GameBoardState extends GameState {
         super(currentGameBoardState.whitePlayer, currentGameBoardState.blackPlayer, currentGameBoardState.gameUuid, 
             message, currentGameBoardState.participants);
 
-        final MoveResult moveResult = GameBoardContract.applyMove(move, currentGameBoardState.getBoard(), currentGameBoardState.getMoveColor());
-        this.moveColor = moveResult.moveColor;
-        this.board = moveResult.board;
+        this.board = new LinkedHashMap<Integer, Stone>(currentGameBoardState.getBoard());
+        this.moveColor = Move.apply(move, this.board, currentGameBoardState.getMoveColor());
 
         this.moveNumber = (currentGameBoardState.moveColor == this.moveColor)
             ? currentGameBoardState.getMoveNumber() // current player has not finished his move jet
@@ -43,7 +42,7 @@ public class GameBoardState extends GameState {
  
     @ConstructorForDeserialization
     public GameBoardState(MemberX500Name whitePlayer, MemberX500Name blackPlayer, 
-            Color moveColor, Integer moveNumber, Map<Integer, Piece> board, String message, 
+            Stone.Color moveColor, Integer moveNumber, Map<Integer, Stone> board, String message, 
             UUID gameUuid, List<PublicKey> participants) {
         super(whitePlayer, blackPlayer, gameUuid, message, participants);
 
@@ -52,7 +51,7 @@ public class GameBoardState extends GameState {
         this.board = board;
     }
 
-    public Piece.Color getMoveColor() {
+    public Stone.Color getMoveColor() {
         return moveColor;
     }
 
@@ -61,10 +60,10 @@ public class GameBoardState extends GameState {
     }
 
     public MemberX500Name getActivePlayerName() {
-        return moveColor == Piece.Color.WHITE ? whitePlayer : blackPlayer;
+        return moveColor == Stone.Color.WHITE ? whitePlayer : blackPlayer;
     }
 
-    public Map<Integer, Piece> getBoard() {
+    public Map<Integer, Stone> getBoard() {
         return board;
     }
 

corda/contracts/src/main/java/djmil/cordacheckers/states/GameState.java

@@ -5,6 +5,7 @@ import java.util.LinkedList;
 import java.util.List;
 import java.util.UUID;
 
+import djmil.cordacheckers.checkers.Stone;
 import net.corda.v5.base.annotations.CordaSerializable;
 import net.corda.v5.base.types.MemberX500Name;
 import net.corda.v5.ledger.utxo.ContractState;
@@ -67,11 +68,11 @@ public abstract class GameState implements ContractState {
         throw new NotInvolved(playerName, this.getClass(), gameUuid);
     }
 
-    public Piece.Color getOpponentColor(MemberX500Name playerName) throws NotInvolved {
+    public Stone.Color getOpponentColor(MemberX500Name playerName) throws NotInvolved {
         if (playerName.compareTo(whitePlayer) == 0)
-            return Piece.Color.BLACK;
+            return Stone.Color.BLACK;
         if (playerName.compareTo(blackPlayer) == 0)
-            return Piece.Color.WHITE;
+            return Stone.Color.WHITE;
         throw new NotInvolved(playerName, this.getClass(), gameUuid);
     }
 

corda/contracts/src/main/java/djmil/cordacheckers/states/Piece.java

@@ -1,64 +0,0 @@
-package djmil.cordacheckers.states;
-
-import net.corda.v5.base.annotations.ConstructorForDeserialization;
-import net.corda.v5.base.annotations.CordaSerializable;
-
-@CordaSerializable
-public class Piece {
-    
-    @CordaSerializable
-    public enum Type {
-        MAN,
-        KING;
-    }
-
-    @CordaSerializable
-    public enum Color {
-        WHITE,
-        BLACK;
-
-        public Color opposite() {
-            switch (this) {
-                case WHITE:
-                    return BLACK;
-                case BLACK:
-                    return WHITE;
-            }
-            throw new RuntimeException("Unknown Color");
-        }
-    }
-
-    private final Color color;
-    private final Type type;
-
-    @ConstructorForDeserialization
-    public Piece(Color color, Type type) {
-        this.color = color;
-        this.type = type;
-    }
-
-    public Color getColor() {
-        return color;
-    }
-
-    public Type getType() {
-        return type;
-    }
-
-    @Override
-    public boolean equals(Object obj) {
-        if (this == obj)
-            return true;
-        if (obj == null)
-            return false;
-        if (getClass() != obj.getClass())
-            return false;
-        Piece other = (Piece) obj;
-        if (color != other.color)
-            return false;
-        if (type != other.type)
-            return false;
-        return true;
-    }
-
-}

corda/workflows/src/main/java/djmil/cordacheckers/gameproposal/CreateFlow.java

@@ -10,13 +10,13 @@ import java.util.UUID;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import djmil.cordacheckers.checkers.Stone;
 import djmil.cordacheckers.contracts.GameCommand;
 import djmil.cordacheckers.gamestate.CommitSubFlow;
 import djmil.cordacheckers.gamestate.FlowResponce;
 import djmil.cordacheckers.gamestate.View;
 import djmil.cordacheckers.gamestate.ViewBuilder;
 import djmil.cordacheckers.states.GameProposalState;
-import djmil.cordacheckers.states.Piece;
 import net.corda.v5.application.flows.ClientRequestBody;
 import net.corda.v5.application.flows.ClientStartableFlow;
 import net.corda.v5.application.flows.CordaInject;
@@ -88,10 +88,10 @@ public class CreateFlow implements ClientStartableFlow{
      private GameProposalState buildGameProposalStateFrom(ClientRequestBody requestBody) {
           final CreateFlowArgs args = requestBody.getRequestBodyAs(jsonMarshallingService, CreateFlowArgs.class);
 
-          final Piece.Color opponentColor = Piece.Color.valueOf(args.opponentColor);
+          final Stone.Color opponentColor = Stone.Color.valueOf(args.opponentColor);
           if (opponentColor == null) {
                throw new RuntimeException("Allowed values for opponentColor are: "
-                    + Piece.Color.WHITE.name() +", "  + Piece.Color.BLACK.name() 
+                    + Stone.Color.WHITE.name() +", "  + Stone.Color.BLACK.name() 
                     + ". Actual value was: " + args.opponentColor);
           }
 
@@ -101,8 +101,8 @@ public class CreateFlow implements ClientStartableFlow{
                "MemberLookup can't find opponentName specified in flow arguments: " + args.opponentName
           );
 
-          final MemberInfo whitePlayerInfo = opponentColor == Piece.Color.WHITE ? opponentInfo : myInfo;
-          final MemberInfo blackPlayerInfo = opponentColor == Piece.Color.BLACK ? opponentInfo : myInfo;
+          final MemberInfo whitePlayerInfo = opponentColor == Stone.Color.WHITE ? opponentInfo : myInfo;
+          final MemberInfo blackPlayerInfo = opponentColor == Stone.Color.BLACK ? opponentInfo : myInfo;
 
           return new GameProposalState(
                whitePlayerInfo.getName(),

corda/workflows/src/main/java/djmil/cordacheckers/gamestate/View.java

@@ -4,10 +4,10 @@ import java.util.List;
 import java.util.Map;
 import java.util.UUID;
 
+import djmil.cordacheckers.checkers.Stone;
 import djmil.cordacheckers.states.GameBoardState;
 import djmil.cordacheckers.states.GameProposalState;
 import djmil.cordacheckers.states.GameResultState;
-import djmil.cordacheckers.states.Piece;
 import net.corda.v5.base.types.MemberX500Name;
 
 // GameBoard from the player's point of view
@@ -27,9 +27,9 @@ public class View {
     public final Status status;
 
     public final String opponentName;
-    public final Piece.Color opponentColor;
+    public final Stone.Color opponentColor;
 
-    public final Map<Integer, Piece> board;
+    public final Map<Integer, Stone> board;
     public final Integer moveNumber;
     public final List<Integer> previousMove;