Fix casting Transformed (#10778)

* Combine casting Transformed into a shared SpellAbility, apply transform effect before spell is cast

* Minor cleanup

* Use effect.apply() rather than game.applyEffects()

* Add test with Maskwood Nexus

Mage/src/main/java/mage/abilities/common/SpellTransformedAbility.java

@@ -0,0 +1,112 @@
+package mage.abilities.common;
+
+import mage.abilities.Ability;
+import mage.abilities.SpellAbility;
+import mage.abilities.costs.mana.ManaCostsImpl;
+import mage.abilities.effects.ContinuousEffectImpl;
+import mage.abilities.keyword.TransformAbility;
+import mage.cards.Card;
+import mage.constants.*;
+import mage.game.Game;
+import mage.game.stack.Spell;
+
+import java.util.UUID;
+
+/**
+ * @author weirddan455, JayDi85, notgreat
+ */
+public class SpellTransformedAbility extends SpellAbility {
+
+    protected final String manaCost; //This variable is only used for rules text
+
+    public SpellTransformedAbility(Card card, String manaCost) {
+        super(card.getSecondFaceSpellAbility());
+        this.newId();
+
+        // getSecondFaceSpellAbility() already verified that second face exists
+        this.setCardName(card.getSecondCardFace().getName());
+
+        this.spellAbilityType = SpellAbilityType.BASE_ALTERNATE;
+        this.setSpellAbilityCastMode(SpellAbilityCastMode.TRANSFORMED);
+
+        this.manaCost = manaCost;
+        this.clearManaCosts();
+        this.clearManaCostsToPay();
+        this.addManaCost(new ManaCostsImpl<>(manaCost));
+        this.addSubAbility(new TransformAbility());
+    }
+
+    public SpellTransformedAbility(final SpellAbility ability) {
+        super(ability);
+        this.newId();
+
+        this.manaCost = null;
+        this.getManaCosts().clear();
+        this.getManaCostsToPay().clear();
+
+        this.spellAbilityType = SpellAbilityType.BASE_ALTERNATE;
+        this.setSpellAbilityCastMode(SpellAbilityCastMode.TRANSFORMED);
+        //when casting this way, the card must have the TransformAbility from elsewhere
+    }
+    protected SpellTransformedAbility(final SpellTransformedAbility ability) {
+        super(ability);
+        this.manaCost = ability.manaCost;
+    }
+
+    @Override
+    public SpellTransformedAbility copy() {
+        return new SpellTransformedAbility(this);
+    }
+
+    @Override
+    public boolean activate(Game game, boolean noMana) {
+        if (super.activate(game, noMana)) {
+            game.getState().setValue(TransformAbility.VALUE_KEY_ENTER_TRANSFORMED + getSourceId(), Boolean.TRUE);
+            // TODO: must be removed after transform cards (one side) migrated to MDF engine (multiple sides)
+            TransformedEffect effect = new TransformedEffect();
+            game.addEffect(effect, this);
+            effect.apply(game, this); //Apply the effect immediately
+            return true;
+        }
+        return false;
+    }
+
+    @Override
+    public ActivationStatus canActivate(UUID playerId, Game game) {
+        if (super.canActivate(playerId, game).canActivate()) {
+            Card card = game.getCard(getSourceId());
+            if (card != null) {
+                return card.getSpellAbility().canActivate(playerId, game);
+            }
+        }
+        return ActivationStatus.getFalse();
+    }
+}
+
+class TransformedEffect extends ContinuousEffectImpl {
+
+    public TransformedEffect() {
+        super(Duration.WhileOnStack, Layer.CopyEffects_1, SubLayer.CopyEffects_1a, Outcome.BecomeCreature);
+        staticText = "";
+    }
+
+    private TransformedEffect(final TransformedEffect effect) {
+        super(effect);
+    }
+
+    @Override
+    public TransformedEffect copy() {
+        return new TransformedEffect(this);
+    }
+
+    @Override
+    public boolean apply(Game game, Ability source) {
+        Spell spell = game.getSpell(source.getSourceId());
+        if (spell == null || spell.getCard().getSecondCardFace() == null) {
+            return false;
+        }
+        // simulate another side as new card (another code part in spell constructor)
+        TransformAbility.transformCardSpellDynamic(spell, spell.getCard().getSecondCardFace(), game);
+        return true;
+    }
+}