/*
    * 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.Arrays;
  import java.util.Iterator;
  
  import org.apache.bcel.Const;
  
  /**
   * This class represents the constant pool, i.e., a table of constants, of a parsed classfile. It may contain null references, due to the JVM specification that
   * skips an entry after an 8-byte constant (double, long) entry. Those interested in generating constant pools programmatically should see
   * <a href="../generic/ConstantPoolGen.html"> ConstantPoolGen</a>.
   *
   * @see Constant
   * @see org.apache.bcel.generic.ConstantPoolGen
   */
  public class ConstantPool implements Cloneable, Node, Iterable<Constant> {
  
      private static String escape(final String str) {
          final int len = str.length();
          final StringBuilder buf = new StringBuilder(len + 5);
          final char[] ch = str.toCharArray();
          for (int i = 0; i < len; i++) {
              switch (ch[i]) {
              case '\n':
                  buf.append("\\n");
                  break;
              case '\r':
                  buf.append("\\r");
                  break;
              case '\t':
                  buf.append("\\t");
                  break;
              case '\b':
                  buf.append("\\b");
                  break;
              case '"':
                  buf.append("\\\"");
                  break;
              default:
                  buf.append(ch[i]);
              }
          }
          return buf.toString();
      }
  
      private Constant[] constantPool;
  
      /**
       * @param constantPool Array of constants
       */
      public ConstantPool(final Constant[] constantPool) {
          setConstantPool(constantPool);
      }
  
      /**
       * Reads constants from given input stream.
       *
       * @param input Input stream
       * @throws IOException if problem in readUnsignedShort or readConstant
       */
      public ConstantPool(final DataInput input) throws IOException {
          byte tag;
          final int constantPoolCount = input.readUnsignedShort();
          constantPool = new Constant[constantPoolCount];
          /*
           * constantPool[0] is unused by the compiler and may be used freely by the implementation.
           * constantPool[0] is currently unused by the implementation.
           */
          for (int i = 1; i < constantPoolCount; i++) {
              constantPool[i] = Constant.readConstant(input);
              /*
               * Quote from the JVM specification: "All eight byte constants take up two spots in the constant pool. If this is the n'th byte in the constant
               * pool, then the next item will be numbered n+2"
               *
               * Thus we have to increment the index counter.
               */
              tag = constantPool[i].getTag();
              if (tag == Const.CONSTANT_Double || tag == Const.CONSTANT_Long) {
                  i++;
              }
         }
     }
 
     /**
      * 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 void accept(final Visitor v) {
         v.visitConstantPool(this);
     }
 
     /**
      * Resolves constant to a string representation.
      *
      * @param c Constant to be printed
      * @return String representation
      * @throws IllegalArgumentException if c is unknown constant type
      */
     public String constantToString(Constant c) throws IllegalArgumentException {
         String str;
         int i;
         final byte tag = c.getTag();
         switch (tag) {
         case Const.CONSTANT_Class:
             i = ((ConstantClass) c).getNameIndex();
             c = getConstantUtf8(i);
             str = Utility.compactClassName(((ConstantUtf8) c).getBytes(), false);
             break;
         case Const.CONSTANT_String:
             i = ((ConstantString) c).getStringIndex();
             c = getConstantUtf8(i);
             str = "\"" + escape(((ConstantUtf8) c).getBytes()) + "\"";
             break;
         case Const.CONSTANT_Utf8:
             str = ((ConstantUtf8) c).getBytes();
             break;
         case Const.CONSTANT_Double:
             str = String.valueOf(((ConstantDouble) c).getBytes());
             break;
         case Const.CONSTANT_Float:
             str = String.valueOf(((ConstantFloat) c).getBytes());
             break;
         case Const.CONSTANT_Long:
             str = String.valueOf(((ConstantLong) c).getBytes());
             break;
         case Const.CONSTANT_Integer:
             str = String.valueOf(((ConstantInteger) c).getBytes());
             break;
         case Const.CONSTANT_NameAndType:
             str = constantToString(((ConstantNameAndType) c).getNameIndex(), Const.CONSTANT_Utf8) + " "
                     + constantToString(((ConstantNameAndType) c).getSignatureIndex(), Const.CONSTANT_Utf8);
             break;
         case Const.CONSTANT_InterfaceMethodref:
         case Const.CONSTANT_Methodref:
         case Const.CONSTANT_Fieldref:
             str = constantToString(((ConstantCP) c).getClassIndex(), Const.CONSTANT_Class) + "."
                     + constantToString(((ConstantCP) c).getNameAndTypeIndex(), Const.CONSTANT_NameAndType);
             break;
         case Const.CONSTANT_MethodHandle:
             // Note that the ReferenceIndex may point to a Fieldref, Methodref or
             // InterfaceMethodref - so we need to peek ahead to get the actual type.
             final ConstantMethodHandle cmh = (ConstantMethodHandle) c;
             str = Const.getMethodHandleName(cmh.getReferenceKind()) + " "
                     + constantToString(cmh.getReferenceIndex(), getConstant(cmh.getReferenceIndex()).getTag());
             break;
         case Const.CONSTANT_MethodType:
             final ConstantMethodType cmt = (ConstantMethodType) c;
             str = constantToString(cmt.getDescriptorIndex(), Const.CONSTANT_Utf8);
             break;
         case Const.CONSTANT_InvokeDynamic:
             final ConstantInvokeDynamic cid = (ConstantInvokeDynamic) c;
             str = cid.getBootstrapMethodAttrIndex() + ":" + constantToString(cid.getNameAndTypeIndex(), Const.CONSTANT_NameAndType);
             break;
         case Const.CONSTANT_Dynamic:
             final ConstantDynamic cd = (ConstantDynamic) c;
             str = cd.getBootstrapMethodAttrIndex() + ":" + constantToString(cd.getNameAndTypeIndex(), Const.CONSTANT_NameAndType);
             break;
         case Const.CONSTANT_Module:
             i = ((ConstantModule) c).getNameIndex();
             c = getConstantUtf8(i);
             str = Utility.compactClassName(((ConstantUtf8) c).getBytes(), false);
             break;
         case Const.CONSTANT_Package:
             i = ((ConstantPackage) c).getNameIndex();
             c = getConstantUtf8(i);
             str = Utility.compactClassName(((ConstantUtf8) c).getBytes(), false);
             break;
         default: // Never reached
             throw new IllegalArgumentException("Unknown constant type " + tag);
         }
         return str;
     }
 
     /**
      * Retrieves constant at 'index' from constant pool and resolve it to a string representation.
      *
      * @param index of constant in constant pool
      * @param tag   expected type
      * @return String representation
      */
     public String constantToString(final int index, final byte tag) {
         return constantToString(getConstant(index, tag));
     }
 
     /**
      * @return deep copy of this constant pool
      */
     public ConstantPool copy() {
         ConstantPool c = null;
         try {
             c = (ConstantPool) clone();
             c.constantPool = new Constant[constantPool.length];
             for (int i = 1; i < constantPool.length; i++) {
                 if (constantPool[i] != null) {
                     c.constantPool[i] = constantPool[i].copy();
                 }
             }
         } catch (final CloneNotSupportedException e) {
             // TODO should this throw?
         }
         return c;
     }
 
     /**
      * Dump constant pool to file stream in binary format.
      *
      * @param file Output file stream
      * @throws IOException if problem in writeShort or dump
      */
     public void dump(final DataOutputStream file) throws IOException {
         /*
          * Constants over the size of the constant pool shall not be written out. This is a redundant measure as the ConstantPoolGen should have already
          * reported an error back in the situation.
          */
         final int size = Math.min(constantPool.length, Const.MAX_CP_ENTRIES);
 
         file.writeShort(size);
         for (int i = 1; i < size; i++) {
             if (constantPool[i] != null) {
                 constantPool[i].dump(file);
             }
         }
     }
 
     /**
      * Gets constant from constant pool.
      *
      * @param index Index in constant pool
      * @return Constant value
      * @see Constant
      * @throws ClassFormatException if index is invalid
      */
     @SuppressWarnings("unchecked")
     public <T extends Constant> T getConstant(final int index) throws ClassFormatException {
         return (T) getConstant(index, Constant.class);
     }
 
     /**
      * Gets constant from constant pool and check whether it has the expected type.
      *
      * @param index Index in constant pool
      * @param tag   Tag of expected constant, i.e., its type
      * @return Constant value
      * @see Constant
      * @throws ClassFormatException if constant type does not match tag
      */
     @SuppressWarnings("unchecked")
     public <T extends Constant> T getConstant(final int index, final byte tag) throws ClassFormatException {
         return (T) getConstant(index, tag, Constant.class);
     }
 
     /**
      * Gets constant from constant pool and check whether it has the expected type.
      *
      * @param index Index in constant pool
      * @param tag   Tag of expected constant, i.e., its type
      * @return Constant value
      * @see Constant
      * @throws ClassFormatException if constant type does not match tag
      * @since 6.6.0
      */
     public <T extends Constant> T getConstant(final int index, final byte tag, final Class<T> castTo) throws ClassFormatException {
         final T c = getConstant(index);
         if (c == null || c.getTag() != tag) {
             throw new ClassFormatException("Expected class '" + Const.getConstantName(tag) + "' at index " + index + " and got " + c);
         }
         return c;
     }
 
     /**
      * Gets constant from constant pool.
      *
      * @param <T> A {@link Constant} subclass
      * @param index Index in constant pool
      * @param castTo The {@link Constant} subclass to cast to.
      * @return Constant value
      * @see Constant
      * @throws ClassFormatException if index is invalid
      * @since 6.6.0
      */
     public <T extends Constant> T getConstant(final int index, final Class<T> castTo) throws ClassFormatException {
         if (index >= constantPool.length || index < 1) {
             throw new ClassFormatException("Invalid constant pool reference using index: " + index + ". Constant pool size is: " + constantPool.length);
         }
         if (constantPool[index] != null && !castTo.isAssignableFrom(constantPool[index].getClass())) {
             throw new ClassFormatException("Invalid constant pool reference at index: " + index +
                     ". Expected " + castTo + " but was " + constantPool[index].getClass());
         }
         if (index > 1) {
             final Constant prev = constantPool[index - 1];
             if (prev != null && (prev.getTag() == Const.CONSTANT_Double || prev.getTag() == Const.CONSTANT_Long)) {
                 throw new ClassFormatException("Constant pool at index " + index + " is invalid. The index is unused due to the preceeding "
                         + Const.getConstantName(prev.getTag()) + ".");
             }
         }
         // Previous check ensures this won't throw a ClassCastException
         final T c = castTo.cast(constantPool[index]);
         if (c == null) {
             throw new ClassFormatException("Constant pool at index " + index + " is null.");
         }
         return c;
     }
 
     /**
      * Gets constant from constant pool and check whether it has the expected type.
      *
      * @param index Index in constant pool
      * @return ConstantInteger value
      * @see ConstantInteger
      * @throws ClassFormatException if constant type does not match tag
      */
     public ConstantInteger getConstantInteger(final int index) {
         return getConstant(index, Const.CONSTANT_Integer, ConstantInteger.class);
     }
 
     /**
      * @return Array of constants.
      * @see Constant
      */
     public Constant[] getConstantPool() {
         return constantPool;
     }
 
     /**
      * Gets string from constant pool and bypass the indirection of 'ConstantClass' and 'ConstantString' objects. I.e. these classes have an index field that
      * points to another entry of the constant pool of type 'ConstantUtf8' which contains the real data.
      *
      * @param index Index in constant pool
      * @param tag   Tag of expected constant, either ConstantClass or ConstantString
      * @return Contents of string reference
      * @see ConstantClass
      * @see ConstantString
      * @throws IllegalArgumentException if tag is invalid
      */
     public String getConstantString(final int index, final byte tag) throws IllegalArgumentException {
         int i;
         /*
          * This switch() is not that elegant, since the four classes have the same contents, they just differ in the name of the index field variable. But we
          * want to stick to the JVM naming conventions closely though we could have solved these more elegantly by using the same variable name or by
          * subclassing.
          */
         switch (tag) {
         case Const.CONSTANT_Class:
             i = getConstant(index, ConstantClass.class).getNameIndex();
             break;
         case Const.CONSTANT_String:
             i = getConstant(index, ConstantString.class).getStringIndex();
             break;
         case Const.CONSTANT_Module:
             i = getConstant(index, ConstantModule.class).getNameIndex();
             break;
         case Const.CONSTANT_Package:
             i = getConstant(index, ConstantPackage.class).getNameIndex();
             break;
         case Const.CONSTANT_Utf8:
             return getConstantUtf8(index).getBytes();
         default:
             throw new IllegalArgumentException("getConstantString called with illegal tag " + tag);
         }
         // Finally get the string from the constant pool
         return getConstantUtf8(i).getBytes();
     }
 
     /**
      * Gets constant from constant pool and check whether it has the expected type.
      *
      * @param index Index in constant pool
      * @return ConstantUtf8 value
      * @see ConstantUtf8
      * @throws ClassFormatException if constant type does not match tag
      */
     public ConstantUtf8 getConstantUtf8(final int index) throws ClassFormatException {
         return getConstant(index, Const.CONSTANT_Utf8, ConstantUtf8.class);
     }
 
     /**
      * @return Length of constant pool.
      */
     public int getLength() {
         return constantPool.length;
     }
 
     @Override
     public Iterator<Constant> iterator() {
         return Arrays.stream(constantPool).iterator();
     }
 
     /**
      * @param constant Constant to set
      */
     public void setConstant(final int index, final Constant constant) {
         constantPool[index] = constant;
     }
 
     /**
      * @param constantPool
      */
     public void setConstantPool(final Constant[] constantPool) {
         this.constantPool = constantPool != null ? constantPool : Constant.EMPTY_ARRAY;
     }
 
     /**
      * @return String representation.
      */
     @Override
     public String toString() {
         final StringBuilder buf = new StringBuilder();
         for (int i = 1; i < constantPool.length; i++) {
             buf.append(i).append(")").append(constantPool[i]).append("\n");
         }
         return buf.toString();
     }
 }