/*
    * 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.bcel.classfile;
  
  import java.io.DataInput;
  import java.io.DataOutputStream;
  import java.io.IOException;
  import java.util.Objects;
  
  import org.apache.bcel.Const;
  import org.apache.bcel.util.BCELComparator;
  
  /**
   * Abstract superclass for classes to represent the different constant types in the constant pool of a class file. The
   * classes keep closely to the JVM specification.
   */
  public abstract class Constant implements Cloneable, Node {
  
      static final Constant[] EMPTY_ARRAY = {};
  
      private static BCELComparator<Constant> bcelComparator = new BCELComparator<Constant>() {
  
          @Override
          public boolean equals(final Constant a, final Constant b) {
              return a == b || a != null && b != null && Objects.equals(a.toString(), b.toString());
          }
  
          @Override
          public int hashCode(final Constant o) {
              return o != null ? Objects.hashCode(o.toString()) : 0;
          }
      };
  
      /**
       * @return Comparison strategy object.
       */
      public static BCELComparator<Constant> getComparator() {
          return bcelComparator;
      }
  
      /**
       * Reads one constant from the given input, the type depends on a tag byte.
       *
       * @param dataInput Input stream
       * @return Constant object
       * @throws IOException if an I/O error occurs reading from the given {@code dataInput}.
       * @throws ClassFormatException if the next byte is not recognized
       * @since 6.0 made public
       */
      public static Constant readConstant(final DataInput dataInput) throws IOException, ClassFormatException {
          final byte b = dataInput.readByte(); // Read tag byte
          switch (b) {
          case Const.CONSTANT_Class:
              return new ConstantClass(dataInput);
          case Const.CONSTANT_Fieldref:
              return new ConstantFieldref(dataInput);
          case Const.CONSTANT_Methodref:
              return new ConstantMethodref(dataInput);
          case Const.CONSTANT_InterfaceMethodref:
              return new ConstantInterfaceMethodref(dataInput);
          case Const.CONSTANT_String:
              return new ConstantString(dataInput);
          case Const.CONSTANT_Integer:
              return new ConstantInteger(dataInput);
          case Const.CONSTANT_Float:
              return new ConstantFloat(dataInput);
          case Const.CONSTANT_Long:
              return new ConstantLong(dataInput);
          case Const.CONSTANT_Double:
              return new ConstantDouble(dataInput);
          case Const.CONSTANT_NameAndType:
              return new ConstantNameAndType(dataInput);
          case Const.CONSTANT_Utf8:
              return ConstantUtf8.getInstance(dataInput);
          case Const.CONSTANT_MethodHandle:
              return new ConstantMethodHandle(dataInput);
          case Const.CONSTANT_MethodType:
              return new ConstantMethodType(dataInput);
          case Const.CONSTANT_Dynamic:
              return new ConstantDynamic(dataInput);
          case Const.CONSTANT_InvokeDynamic:
              return new ConstantInvokeDynamic(dataInput);
          case Const.CONSTANT_Module:
              return new ConstantModule(dataInput);
          case Const.CONSTANT_Package:
             return new ConstantPackage(dataInput);
         default:
             throw new ClassFormatException("Invalid byte tag in constant pool: " + b);
         }
     }
 
     /**
      * @param comparator Comparison strategy object
      */
     public static void setComparator(final BCELComparator<Constant> comparator) {
         bcelComparator = comparator;
     }
 
     /*
      * In fact this tag is redundant since we can distinguish different 'Constant' objects by their type, i.e., via
      * 'instanceof'. In some places we will use the tag for switch()es anyway.
      *
      * First, we want match the specification as closely as possible. Second we need the tag as an index to select the
      * corresponding class name from the 'CONSTANT_NAMES' array.
      */
     /**
      * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
      */
     @java.lang.Deprecated
     protected byte tag; // TODO should be private & final
 
     Constant(final byte tag) {
         this.tag = tag;
     }
 
     /**
      * Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class.
      * I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
      *
      * @param v Visitor object
      */
     @Override
     public abstract void accept(Visitor v);
 
     @Override
     public Object clone() {
         try {
             return super.clone();
         } catch (final CloneNotSupportedException e) {
             throw new UnsupportedOperationException("Clone Not Supported", e); // never happens
         }
     }
 
     /**
      * @return deep copy of this constant
      */
     public Constant copy() {
         try {
             return (Constant) super.clone();
         } catch (final CloneNotSupportedException e) {
             // TODO should this throw?
         }
         return null;
     }
 
     public abstract void dump(DataOutputStream file) throws IOException;
 
     /**
      * Returns value as defined by given BCELComparator strategy. By default two Constant objects are said to be equal when
      * the result of toString() is equal.
      *
      * @see Object#equals(Object)
      */
     @Override
     public boolean equals(final Object obj) {
         return obj instanceof Constant && bcelComparator.equals(this, (Constant) obj);
     }
 
     /**
      * @return Tag of constant, i.e., its type. No setTag() method to avoid confusion.
      */
     public final byte getTag() {
         return tag;
     }
 
     /**
      * Returns value as defined by given BCELComparator strategy. By default return the hash code of the result of
      * toString().
      *
      * @see Object#hashCode()
      */
     @Override
     public int hashCode() {
         return bcelComparator.hashCode(this);
     }
 
     /**
      * @return String representation.
      */
     @Override
     public String toString() {
         return Const.getConstantName(tag) + "[" + tag + "]";
     }
 }