refactor: added code example for rules auto-replacement in creature's ETB (related to #12791)

Mage/src/main/java/mage/abilities/TriggeredAbility.java

@@ -104,4 +104,6 @@ public interface TriggeredAbility extends Ability {
     GameEvent getTriggerEvent();
 
     TriggeredAbility setTriggerPhrase(String triggerPhrase);
+
+    String getTriggerPhrase();
 }

Mage/src/main/java/mage/abilities/TriggeredAbilityImpl.java

@@ -132,6 +132,11 @@ public abstract class TriggeredAbilityImpl extends AbilityImpl implements Trigge
         return this;
     }
 
+    @Override
+    public String getTriggerPhrase() {
+        return this.triggerPhrase;
+    }
+
     @Override
     public void setTriggerEvent(GameEvent triggerEvent) {
         this.triggerEvent = triggerEvent;

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

@@ -17,7 +17,11 @@ public class EntersBattlefieldTriggeredAbility extends TriggeredAbilityImpl {
 
     public EntersBattlefieldTriggeredAbility(Effect effect, boolean optional) {
         super(Zone.ALL, effect, optional); // Zone.All because a creature with trigger can be put into play and be sacrificed during the resolution of an effect (discard Obstinate Baloth with Smallpox)
-        this.withRuleTextReplacement(true); // default true to replace "{this}" with "it"
+        this.withRuleTextReplacement(true); // default true to replace "{this}" with "it" or "this creature"
+
+        // warning, it's impossible to add text auto-replacement for creatures here (When this creature enters),
+        // so it was implemented in CardImpl.addAbility instead
+        // see https://github.com/magefree/mage/issues/12791
         setTriggerPhrase("When {this} enters, ");
     }
 

Mage/src/main/java/mage/cards/CardImpl.java

@@ -343,6 +343,20 @@ public abstract class CardImpl extends MageObjectImpl implements Card {
                 }
             }
         }
+
+        // rules fix: workaround to add text auto-replacement for creature's ETB
+        if (this.isCreature() && ability.getRule().startsWith("When {this} enters") && ability instanceof  TriggeredAbility) {
+            TriggeredAbility triggeredAbility = ((TriggeredAbility) ability);
+            if (triggeredAbility.getTriggerPhrase() != null) {
+                // TODO: delete or enable after wizards update all cards, not last sets only, see https://github.com/magefree/mage/issues/12791
+                //triggeredAbility.setTriggerPhrase(triggeredAbility.getTriggerPhrase().replace("{this}", "this creature"));
+            }
+        }
+        // verify check: all creatures with ETB must use "When this creature enters" instead "When {this} enters"
+        if (this.isCreature() && ability.getRule().startsWith("When {this} enters")) {
+            // see above
+            //throw new IllegalArgumentException("Wrong code usage: creature's ETB ability must use text like \"When this creature enters\"");
+        }
     }
 
     protected void addAbility(Ability ability, Watcher watcher) {