Implement completely useless global value copying

src/main/java/emu/grasscutter/game/ability/actions/AbilityActionHandler.java

@@ -6,7 +6,29 @@ import emu.grasscutter.game.ability.Ability;
 import emu.grasscutter.game.entity.GameEntity;
 
 public abstract class AbilityActionHandler {
-
     public abstract boolean execute(
             Ability ability, AbilityModifierAction action, ByteString abilityData, GameEntity target);
+
+    /**
+     * Returns the target entity.
+     *
+     * @param ability The ability being invoked.
+     * @param entity The entity invoking the ability.
+     * @param target The target entity type.
+     * @return The target entity.
+     */
+    protected GameEntity getTarget(Ability ability, GameEntity entity, String target) {
+        return switch (target) {
+            default -> throw new RuntimeException("Unknown target type: " + target);
+            case "Self" -> entity;
+            case "Team" -> ability.getPlayerOwner().getTeamManager().getEntity();
+            case "OriginOwner" -> ability.getPlayerOwner()
+                .getTeamManager().getCurrentAvatarEntity();
+            case "Owner" -> ability.getOwner();
+            case "Applier" -> entity; // TODO: Validate.
+            case "CurLocalAvatar" -> ability.getPlayerOwner()
+                .getTeamManager().getCurrentAvatarEntity(); // TODO: Validate.
+            case "CasterOriginOwner" -> null; // TODO: Figure out.
+        };
+    }
 }

src/main/java/emu/grasscutter/game/ability/actions/ActionCopyGlobalValue.java

@@ -0,0 +1,33 @@
+package emu.grasscutter.game.ability.actions;
+
+import com.google.protobuf.ByteString;
+import emu.grasscutter.Grasscutter;
+import emu.grasscutter.data.binout.AbilityModifier.AbilityModifierAction;
+import emu.grasscutter.game.ability.Ability;
+import emu.grasscutter.game.entity.GameEntity;
+
+@AbilityAction(AbilityModifierAction.Type.CopyGlobalValue)
+public final class ActionCopyGlobalValue extends AbilityActionHandler {
+    @Override
+    public boolean execute(Ability ability, AbilityModifierAction action, ByteString abilityData, GameEntity entity) {
+        // Get the entities referred to.
+        var source = this.getTarget(ability, entity, action.srcTarget);
+        var destination = this.getTarget(ability, entity, action.dstTarget);
+        // Check the entities.
+        if (source == null || destination == null) {
+            Grasscutter.getLogger().debug("ActionCopyGlobalValue: source or destination is null");
+            return false;
+        }
+
+        // Get the global value.
+        var value = source.getGlobalAbilityValues().get(action.srcKey);
+        if (value == null) {
+            Grasscutter.getLogger().debug("ActionCopyGlobalValue: source value is null");
+            return false;
+        }
+
+        // Apply the new global value.
+        destination.getGlobalAbilityValues().put(action.dstKey, value);
+        return true;
+    }
+}