Implement Impending mechanic (#12865)

* implement Impending mechanic

* add initial test

* add more tests

* small fix

Mage/src/main/java/mage/abilities/costs/AlternativeSourceCostsImpl.java

@@ -30,11 +30,15 @@ public abstract class AlternativeSourceCostsImpl extends StaticAbility implement
     }
 
     protected AlternativeSourceCostsImpl(String name, String reminderText, Cost cost) {
+        this(name, reminderText, cost, name);
+    }
+
+    protected AlternativeSourceCostsImpl(String name, String reminderText, Cost cost, String activationKey) {
         super(Zone.ALL, null);
         this.name = name;
         this.reminderText = reminderText;
         this.alternativeCost = new AlternativeCostImpl<>(name, reminderText, cost);
-        this.activationKey = getActivationKey(name);
+        this.activationKey = getActivationKey(activationKey);
     }
 
     protected AlternativeSourceCostsImpl(final AlternativeSourceCostsImpl ability) {

Mage/src/main/java/mage/abilities/keyword/ImpendingAbility.java

@@ -1,12 +1,33 @@
 package mage.abilities.keyword;
 
 import mage.abilities.Ability;
+import mage.abilities.common.BeginningOfEndStepTriggeredAbility;
+import mage.abilities.common.EntersBattlefieldAbility;
+import mage.abilities.common.SimpleStaticAbility;
+import mage.abilities.condition.Condition;
+import mage.abilities.condition.common.SourceHasCounterCondition;
 import mage.abilities.costs.AlternativeSourceCostsImpl;
+import mage.abilities.costs.mana.ManaCostsImpl;
+import mage.abilities.decorator.ConditionalOneShotEffect;
+import mage.abilities.effects.ContinuousEffectImpl;
+import mage.abilities.effects.common.AddContinuousEffectToGame;
+import mage.abilities.effects.common.counter.AddCountersSourceEffect;
+import mage.abilities.effects.common.counter.RemoveCounterSourceEffect;
+import mage.constants.*;
+import mage.counters.CounterType;
 import mage.game.Game;
+import mage.game.permanent.Permanent;
 import mage.util.CardUtil;
 
+import java.util.stream.Collectors;
+
 /**
- * TODO: Implement this
+ * "Impending N–[cost]" is a keyword that represents multiple abilities.
+ * The official rules are as follows:
+ * (a) You may choose to pay [cost] rather than pay this spell's mana cost.
+ * (b) If you chose to pay this spell's impending cost, it enters the battlefield with N time counters on it.
+ * (c) As long as this permanent has a time counter on it, if it was cast for its impending cost, it's not a creature.
+ * (d) At the beginning of your end step, if this permanent was cast for its impending cost, remove a time counter from it. Then if it has no time counters on it, it loses impending.
  *
  * @author TheElk801
  */
@@ -16,14 +37,24 @@ public class ImpendingAbility extends AlternativeSourceCostsImpl {
     private static final String IMPENDING_REMINDER = "If you cast this spell for its impending cost, " +
             "it enters with %s time counters and isn't a creature until the last is removed. " +
             "At the beginning of your end step, remove a time counter from it.";
+    private static final Condition counterCondition = new SourceHasCounterCondition(CounterType.TIME, 0, 0);
 
-    public ImpendingAbility(String manaString) {
-        this(manaString, 4);
-    }
-
-    public ImpendingAbility(String manaString, int amount) {
-        super(IMPENDING_KEYWORD + ' ' + amount, String.format(IMPENDING_REMINDER, CardUtil.numberToText(amount)), manaString);
+    public ImpendingAbility(int amount, String manaString) {
+        super(IMPENDING_KEYWORD + ' ' + amount, String.format(IMPENDING_REMINDER, CardUtil.numberToText(amount)), new ManaCostsImpl<>(manaString), IMPENDING_KEYWORD);
         this.setRuleAtTheTop(true);
+        this.addSubAbility(new EntersBattlefieldAbility(new ConditionalOneShotEffect(
+                new AddCountersSourceEffect(CounterType.TIME.createInstance(amount)), ImpendingCondition.instance, ""
+        ), "").setRuleVisible(false));
+        this.addSubAbility(new SimpleStaticAbility(new ImpendingAbilityTypeEffect()).setRuleVisible(false));
+        Ability ability = new BeginningOfEndStepTriggeredAbility(
+                new RemoveCounterSourceEffect(CounterType.TIME.createInstance()),
+                TargetController.YOU, ImpendingCondition.instance, false
+        );
+        ability.addEffect(new ConditionalOneShotEffect(
+                new AddContinuousEffectToGame(new ImpendingAbilityRemoveEffect()),
+                counterCondition, "Then if it has no time counters on it, it loses impending"
+        ));
+        this.addSubAbility(ability.setRuleVisible(false));
     }
 
     private ImpendingAbility(final ImpendingAbility ability) {
@@ -35,12 +66,81 @@ public class ImpendingAbility extends AlternativeSourceCostsImpl {
         return new ImpendingAbility(this);
     }
 
-    @Override
-    public boolean isAvailable(Ability source, Game game) {
-        return true;
-    }
-
     public static String getActivationKey() {
         return getActivationKey(IMPENDING_KEYWORD);
     }
 }
+
+enum ImpendingCondition implements Condition {
+    instance;
+
+    @Override
+    public boolean apply(Game game, Ability source) {
+        return CardUtil.checkSourceCostsTagExists(game, source, ImpendingAbility.getActivationKey());
+    }
+}
+
+class ImpendingAbilityTypeEffect extends ContinuousEffectImpl {
+
+    ImpendingAbilityTypeEffect() {
+        super(Duration.WhileOnBattlefield, Layer.TypeChangingEffects_4, SubLayer.NA, Outcome.Detriment);
+        staticText = "As long as this permanent has a time counter on it, if it was cast for its impending cost, it's not a creature.";
+    }
+
+    private ImpendingAbilityTypeEffect(final ImpendingAbilityTypeEffect effect) {
+        super(effect);
+    }
+
+    @Override
+    public ImpendingAbilityTypeEffect copy() {
+        return new ImpendingAbilityTypeEffect(this);
+    }
+
+    @Override
+    public boolean apply(Game game, Ability source) {
+        if (!ImpendingCondition.instance.apply(game, source)) {
+            return false;
+        }
+        Permanent permanent = source.getSourcePermanentIfItStillExists(game);
+        if (permanent.getCounters(game).getCount(CounterType.TIME) < 1) {
+            return false;
+        }
+        permanent.removeCardType(game, CardType.CREATURE);
+        permanent.removeAllCreatureTypes(game);
+        return true;
+    }
+}
+
+class ImpendingAbilityRemoveEffect extends ContinuousEffectImpl {
+
+    ImpendingAbilityRemoveEffect() {
+        super(Duration.Custom, Layer.AbilityAddingRemovingEffects_6, SubLayer.NA, Outcome.LoseAbility);
+    }
+
+    private ImpendingAbilityRemoveEffect(final ImpendingAbilityRemoveEffect effect) {
+        super(effect);
+    }
+
+    @Override
+    public ImpendingAbilityRemoveEffect copy() {
+        return new ImpendingAbilityRemoveEffect(this);
+    }
+
+    @Override
+    public boolean apply(Game game, Ability source) {
+        Permanent permanent = source.getSourcePermanentIfItStillExists(game);
+        if (permanent == null) {
+            discard();
+            return false;
+        }
+        permanent.removeAbilities(
+                permanent
+                        .getAbilities(game)
+                        .stream()
+                        .filter(ImpendingAbility.class::isInstance)
+                        .collect(Collectors.toList()),
+                source.getSourceId(), game
+        );
+        return true;
+    }
+}