From 8affa353dae54da970cacfe542b8978d5e092f9c Mon Sep 17 00:00:00 2001
From: djmil <andriy@djmil.dev>
Date: Fri, 29 Sep 2023 13:59:34 +0200
Subject: [PATCH] move: mandatory capture

---
 .../djmil/cordacheckers/CheckersMoveTest.java |  2 +-
 .../cordaclient/GameBoardTests.java           | 16 +++++++++
 .../djmil/cordacheckers/checkers/Move.java    | 33 +++++++++++++++++--
 3 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/backend/src/test/java/djmil/cordacheckers/CheckersMoveTest.java b/backend/src/test/java/djmil/cordacheckers/CheckersMoveTest.java
index 2c020ac..815cc24 100644
--- a/backend/src/test/java/djmil/cordacheckers/CheckersMoveTest.java
+++ b/backend/src/test/java/djmil/cordacheckers/CheckersMoveTest.java
@@ -21,7 +21,7 @@ public class CheckersMoveTest {
         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(5, Arrays.asList(1, 9, 14)),
         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)),
diff --git a/backend/src/test/java/djmil/cordacheckers/cordaclient/GameBoardTests.java b/backend/src/test/java/djmil/cordacheckers/cordaclient/GameBoardTests.java
index 3d9ccfd..c5753c2 100644
--- a/backend/src/test/java/djmil/cordacheckers/cordaclient/GameBoardTests.java
+++ b/backend/src/test/java/djmil/cordacheckers/cordaclient/GameBoardTests.java
@@ -110,6 +110,22 @@ public class GameBoardTests {
         assertThat(m2.board().get(15)).isEqualTo(BLACK_MAN);
         assertThat(m2.moveNumber() == 2);
         assertThat(m2.status()).isEqualByComparingTo(Status.GAME_BOARD_WAIT_FOR_OPPONENT);
+
+        assertThatThrownBy(() -> { 
+            cordaClient.gameBoardMove(hiWhite, game.uuid(), move(24, 19), 
+            "An attempt to ignore mandatory capture");
+        });
+
+        final var m3 = cordaClient.gameBoardMove(hiWhite, game.uuid(), move(18, 11), null);
+        assertThat(m2.board().get(18)).isEqualTo(WHITE_MAN);
+        assertThat(m2.board().get(11)).isNull();
+        assertThat(m2.board().get(15)).isEqualTo(BLACK_MAN);
+        assertThat(m3.board().get(11)).isEqualTo(WHITE_MAN);
+        assertThat(m3.board().get(18)).isNull();
+        assertThat(m3.board().get(15)).isNull();
+        assertThat(m3.moveNumber() == 3);
+        assertThat(m3.status()).isEqualByComparingTo(Status.GAME_BOARD_WAIT_FOR_OPPONENT);
+
     }
 
     ArrayList<Integer> move(int from, int to) {
diff --git a/corda/contracts/src/main/java/djmil/cordacheckers/checkers/Move.java b/corda/contracts/src/main/java/djmil/cordacheckers/checkers/Move.java
index d6e4196..91bafb5 100644
--- a/corda/contracts/src/main/java/djmil/cordacheckers/checkers/Move.java
+++ b/corda/contracts/src/main/java/djmil/cordacheckers/checkers/Move.java
@@ -42,7 +42,9 @@ public class Move {
         if (!allMoves.contains(this))
             throw new Exception("Prohibited move");
 
-        // TODO: check for mandatory captures
+        final Set<Move> mandatoryJumps = getMandatoryJumps(board, expectedMoveColor);
+        if (mandatoryJumps.size() != 0 && !mandatoryJumps.contains(this))
+            throw new Exception("A mandatory opponent's stone capture must be performed");
 
         movingStone = movingStone.promoteIfPossible(to);
         if (board.put(to, movingStone) != null)
@@ -66,7 +68,7 @@ public class Move {
 
         intersection.retainAll(b);
         if (intersection.size() != 1)
-            // A legit move is characterized by single intersection point
+            // A legit move is characterized by a single intersection point
             throw new Exception("Prohibited move");
         
         return intersection.iterator().next();
@@ -113,7 +115,7 @@ public class Move {
         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(5, Arrays.asList(1, 9, 14)),
         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)),
@@ -149,6 +151,31 @@ public class Move {
         }
     }
 
+    public static Set<Move> getMandatoryJumps(Map<Integer, Stone> board, Stone.Color color) {
+        Set<Move> res = new HashSet<Move>();
+
+        for (Map.Entry<Integer, Stone> entry : board.entrySet()) {
+            final Integer from = entry.getKey();
+            final Stone  stone = entry.getValue();
+            if (stone.getColor() != color)
+                continue;
+
+            final Stone.Color opponentsColor = color.opposite();
+            final Set<Move> allJumps = stone.getJumps(from);
+
+            allJumps.removeIf( j -> {
+                if (board.get(j.to) != null) 
+                    return true;    // must be an empty jumpTo tile
+                final Stone jumpOverStone = board.get(j.jumpOver);
+                return jumpOverStone == null || jumpOverStone.getColor() != opponentsColor;
+            });
+
+            res.addAll(allJumps);
+        }
+
+        return res;
+    }
+
     @Override
     public int hashCode() {
         final int prime = 31;