/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.scxml2.model;
  
  import java.io.Serializable;
  
  /**
   * An abstract base class for elements in SCXML that can serve as a
   * <target> for a <transition>, such as State or Parallel.
   *
   */
  public abstract class TransitionTarget implements Serializable, Observable {
  
      private static final EnterableState[] ZERO_ANCESTORS = new EnterableState[0];
  
      /**
       * The id for this {@link Observable} which is unique within the SCXML state machine
       */
      private Integer observableId;
  
      /**
       * Identifier for this transition target. Other parts of the SCXML
       * document may refer to this <state> using this ID.
       */
      private String id;
  
      /**
       * The parent of this transition target (may be null, if the parent
       * is the SCXML document root).
       */
      private EnterableState parent;
  
      private EnterableState[] ancestors = ZERO_ANCESTORS;
  
      /**
       * Constructor.
       */
      public TransitionTarget() {
          super();
          parent = null;
      }
  
      /**
       * {@inheritDoc}
       */
      public final Integer getObservableId() {
          return observableId;
      }
  
      /**
       * Sets the observableId for this Observable, which must be unique within the SCXML state machine
       * @param observableId the observableId
       */
      public final void setObservableId(Integer observableId) {
          this.observableId = observableId;
      }
  
      /**
       * Get the identifier for this transition target (may be null).
       *
       * @return Returns the id.
       */
      public final String getId() {
          return id;
      }
  
      /**
       * Set the identifier for this transition target.
       *
       * @param id The id to set.
       */
      public final void setId(final String id) {
          this.id = id;
      }
  
      /**
       * @return the number of TransitionTarget ancestors
       */
      public int getNumberOfAncestors() {
          return ancestors.length;
      }
  
      /**
       * Get the ancestor of this TransitionTarget at specified level
       * @param level the level of the ancestor to return, zero being top
      * @return the ancestor at specified level
      */
     public EnterableState getAncestor(int level) {
         return ancestors[level];
     }
 
     /**
      * Get the parent TransitionTarget.
      *
      * @return Returns the parent state
      * (null if parent is <scxml> element)
      */
     public EnterableState getParent() {
         return parent;
     }
 
     /**
      * Set the parent EnterableState.
      * <p>
      * The parent of a TransitionTarget must be of type EnterableState as a History (as only non-EnterableState)
      * TransitionTarget cannot have children.
      * </p>
      *
      * @param parent The parent state to set
      */
     protected void setParent(final EnterableState parent) {
         if (parent == null) {
             throw new IllegalArgumentException("Parent parameter cannot be null");
         }
         if (parent == this) {
             throw new IllegalArgumentException("Cannot set self as parent");
         }
         if (this.parent != parent) {
             this.parent = parent;
             updateDescendantsAncestors();
         }
     }
 
     /**
      * Update TransitionTarget descendants their ancestors
      */
     protected void updateDescendantsAncestors() {
         TransitionTarget ttParent = parent;
         ancestors = new EnterableState[ttParent.ancestors.length+1];
         System.arraycopy(ttParent.ancestors, 0, ancestors, 0, ttParent.ancestors.length);
         ancestors[ttParent.ancestors.length] = parent;
     }
 
     /**
      * Checks whether this transition target (State or Parallel) is a
      * descendant of the transition target context.
      *
      * @param context
      *            TransitionTarget context - a potential ancestor
      * @return true if this is a descendant of context, false otherwise
      */
     public final boolean isDescendantOf(TransitionTarget context) {
         return getNumberOfAncestors() > context.getNumberOfAncestors()
                 && getAncestor(context.getNumberOfAncestors()) == context;
     }
     
     /**
      * Enforce identity equality only
      * @param other other object to compare with
      * @return this == other
      */
     @Override
     public final boolean equals(final Object other) {
         return this == other;
     }
 
     /**
      * Enforce returning identity based hascode
      * @return {@link System#identityHashCode(Object) System.identityHashCode(this)}
      */
     @Override
     public final int hashCode() {
         return System.identityHashCode(this);
     }
 }