Fix simulation AI exception with random effects.

Uses a seeded deterministic random generator when simulating choices, which ensures  the same number of sub-choices are always used, which the code requires. Adds a test.

forge-ai/src/main/java/forge/ai/simulation/SpellAbilityPicker.java

@@ -1,8 +1,10 @@
 package forge.ai.simulation;
 
+import forge.util.MyRandom;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Random;
 import java.util.Set;
 
 import forge.ai.AiPlayDecision;
@@ -363,10 +365,17 @@ public class SpellAbilityPicker {
         controller.evaluateSpellAbility(saList, saIndex);
         SpellAbility sa = saList.get(saIndex);
 
+        // Use a deterministic random seed when evaluating different choices of a spell ability.
+        // This is needed as otherwise random effects may result in a different number of choices
+        // each iteration, which will break the logic in SpellAbilityChoicesIterator.
+        Random origRandom = MyRandom.getRandom();
+        long randomSeedToUse = origRandom.nextLong();
+
         Score bestScore = new Score(Integer.MIN_VALUE);
         final SpellAbilityChoicesIterator choicesIterator = new SpellAbilityChoicesIterator(controller);
-        Score lastScore = null;
+        Score lastScore;
         do {
+            MyRandom.setRandom(new Random(randomSeedToUse));
             GameSimulator simulator = new GameSimulator(controller, game, player, phase);
             simulator.setInterceptor(choicesIterator);
             lastScore = simulator.simulateSpellAbility(sa);
@@ -375,6 +384,7 @@ public class SpellAbilityPicker {
             }
         } while (choicesIterator.advance(lastScore));
         controller.doneEvaluating(bestScore);
+        MyRandom.setRandom(origRandom);
         return bestScore;
     }
 

forge-core/src/main/java/forge/util/MyRandom.java

@@ -39,8 +39,7 @@ public class MyRandom {
      * If percent is like 30, then 30% of the time it will be true.
      * </p>
      * 
-     * @param percent
-     *            a int.
+     * @param percent an int.
      * @return a boolean.
      */
     public static boolean percentTrue(final int percent) {
@@ -56,6 +55,14 @@ public class MyRandom {
         return MyRandom.random;
     }
 
+    /**
+     * Sets the random provider. Used for deterministic simulation.
+     * @param random the random
+     */
+    public static void setRandom(Random random) {
+        MyRandom.random = random;
+    }
+
     public static int[] splitIntoRandomGroups(final int value, final int numGroups) {
         int[] groups = new int[numGroups];
         

forge-gui-desktop/src/test/java/forge/ai/simulation/SpellAbilityPickerSimulationTest.java

@@ -439,4 +439,50 @@ public class SpellAbilityPickerSimulationTest extends SimulationTest {
         AssertJUnit.assertEquals("Destroy target nonblack creature.", sa.toString());
         AssertJUnit.assertEquals(blocker, sa.getTargetCard());
     }
+
+    @Test
+    public void testChoicesResultingFromRandomEffects() {
+        // Sometimes, the effect of a spell can be random, and as a result of that, new choices
+        // could be selected during simulation. This test verifies that this doesn't cause problems.
+        //
+        // Note: The current implementation works around the issue by setting a consistent random
+        // seed during choice evaluation, although in the future, it may make sense to handle it
+        // some other way.
+
+        // Run the test 100 times to ensure there's no flakiness.
+        for (int i = 0; i < 100; i++) {
+            Game game = initAndCreateGame();
+            Player p = game.getPlayers().get(1);
+            Player opponent = game.getPlayers().get(0);
+
+            addCardToZone("Chaos Warp", p, ZoneType.Hand);
+            addCard("Mountain", p);
+            addCard("Mountain", p);
+            addCard("Mountain", p);
+
+            addCard("Plains", opponent);
+            addCard("Mountain", opponent);
+            addCard("Forest", opponent);
+            // Use a card that is worthwhile to target even if the shuffle ends up choosing it
+            // again. In this case, life loss on ETB and leaving.
+            Card expectedTarget = addCard("Raving Oni-Slave", opponent);
+
+            addCardToZone("Chaos Warp", opponent, ZoneType.Library);
+            addCardToZone("Island", opponent, ZoneType.Library);
+            addCardToZone("Swamp", opponent, ZoneType.Library);
+            // The presence of Pilgrim's Eye in the library is important for this test, as this
+            // will result in sub-choices (which land to pick) if this card ends up being the top
+            // of the library during simulation.
+            addCardToZone("Pilgrim's Eye", opponent, ZoneType.Library);
+
+            game.getPhaseHandler().devModeSet(PhaseType.MAIN2, p);
+            game.getAction().checkStateEffects(true);
+
+            SpellAbilityPicker picker = new SpellAbilityPicker(game, p);
+            SpellAbility sa = picker.chooseSpellAbilityToPlay(null);
+            AssertJUnit.assertNotNull(sa);
+            AssertJUnit.assertEquals("Chaos Warp", sa.getHostCard().getName());
+            AssertJUnit.assertEquals(expectedTarget, sa.getTargetCard());
+        }
+    }
 }