/*
    * 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.jxpath.ri.axes;
  
  import org.apache.commons.jxpath.Function;
  import org.apache.commons.jxpath.JXPathContext;
  import org.apache.commons.jxpath.NodeSet;
  import org.apache.commons.jxpath.ri.EvalContext;
  import org.apache.commons.jxpath.ri.JXPathContextReferenceImpl;
  import org.apache.commons.jxpath.ri.QName;
  import org.apache.commons.jxpath.ri.model.NodePointer;
  
  /**
   * EvalContext that is used to hold the root node for the path traversal.
   */
  public class RootContext extends EvalContext {
  
      /**
       * Unknown value marker.
       */
      public static final Object UNKNOWN_VALUE = new Object();
  
      private static final int MAX_REGISTER = 4;
      private final JXPathContextReferenceImpl jxpathContext;
      private final NodePointer pointer;
      private Object[] registers;
      private int availableRegister;
  
      /**
       * Constructs a new RootContext.
       *
       * @param jxpathContext context
       * @param pointer       pointer
       */
      public RootContext(final JXPathContextReferenceImpl jxpathContext, final NodePointer pointer) {
          super(null);
          this.jxpathContext = jxpathContext;
          this.pointer = pointer;
          if (pointer != null) {
              pointer.setNamespaceResolver(jxpathContext.getNamespaceResolver());
          }
      }
  
      /**
       * Gets absolute root context
       *
       * @return EvalContext
       */
      public EvalContext getAbsoluteRootContext() {
          return jxpathContext.getAbsoluteRootContext();
      }
  
      /**
       * Gets a context that points to the specified object.
       *
       * @param constant object
       * @return EvalContext
       */
      public EvalContext getConstantContext(final Object constant) {
          if (constant instanceof NodeSet) {
              return new NodeSetContext(new RootContext(jxpathContext, null), (NodeSet) constant);
          }
          NodePointer pointer;
          if (constant instanceof NodePointer) {
              pointer = (NodePointer) constant;
          } else {
              pointer = NodePointer.newNodePointer(new QName(null, ""), constant, null);
          }
          return new InitialContext(new RootContext(jxpathContext, pointer));
      }
  
      @Override
      public NodePointer getCurrentNodePointer() {
          return pointer;
      }
  
      @Override
      public int getCurrentPosition() {
          throw new UnsupportedOperationException();
      }
  
      /**
       * Gets the specified function from the context.
       *
      * @param functionName QName
      * @param parameters   Object[]
      * @return Function
      */
     public Function getFunction(final QName functionName, final Object[] parameters) {
         return jxpathContext.getFunction(functionName, parameters);
     }
 
     @Override
     public JXPathContext getJXPathContext() {
         return jxpathContext;
     }
 
     /**
      * Gets a registered value.
      *
      * @param id int
      * @return Object
      */
     public Object getRegisteredValue(final int id) {
         if (registers == null || id >= MAX_REGISTER || id == -1) {
             return UNKNOWN_VALUE;
         }
         return registers[id];
     }
 
     @Override
     public RootContext getRootContext() {
         return this;
     }
 
     @Override
     public Object getValue() {
         return pointer;
     }
 
     /**
      * Gets variable context.
      *
      * @param variableName variable name
      * @return EvalContext
      */
     public EvalContext getVariableContext(final QName variableName) {
         return new InitialContext(new RootContext(jxpathContext, jxpathContext.getVariablePointer(variableName)));
     }
 
     @Override
     public boolean nextNode() {
         throw new UnsupportedOperationException();
     }
 
     @Override
     public boolean nextSet() {
         throw new UnsupportedOperationException();
     }
 
     @Override
     public boolean setPosition(final int position) {
         throw new UnsupportedOperationException();
     }
 
     /**
      * Sets the next registered value.
      *
      * @param value Object
      * @return the id that can reclaim value.
      */
     public int setRegisteredValue(final Object value) {
         if (registers == null) {
             registers = new Object[MAX_REGISTER];
             for (int i = 0; i < MAX_REGISTER; i++) {
                 registers[i] = UNKNOWN_VALUE;
             }
         }
         if (availableRegister >= MAX_REGISTER) {
             return -1;
         }
         registers[availableRegister] = value;
         availableRegister++;
         return availableRegister - 1;
     }
 
     @Override
     public String toString() {
         return super.toString() + ":" + pointer.asPath();
     }
 }