/*
    * 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
    *
   *   https://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.HashMap;
  import java.util.LinkedHashMap;
  import java.util.Map;
  import java.util.Objects;
  
  import org.apache.bcel.Const;
  
  /**
   * Extends the abstract {@link Constant} to represent a reference to a UTF-8 encoded string.
   * <p>
   * The following system properties govern caching this class performs.
   * </p>
   * <ul>
   * <li>{@link #SYS_PROP_CACHE_MAX_ENTRIES} (since 6.4): The size of the cache, by default 0, meaning caching is
   * disabled.</li>
   * <li>{@link #SYS_PROP_CACHE_MAX_ENTRY_SIZE} (since 6.0): The maximum size of the values to cache, by default 200, 0
   * disables caching. Values larger than this are <em>not</em> cached.</li>
   * <li>{@link #SYS_PROP_STATISTICS} (since 6.0): Prints statistics on the console when the JVM exits.</li>
   * </ul>
   * <p>
   * Here is a sample Maven invocation with caching disabled:
   * </p>
   *
   * <pre>
   * mvn test -Dbcel.statistics=true -Dbcel.maxcached.size=0 -Dbcel.maxcached=0
   * </pre>
   * <p>
   * Here is a sample Maven invocation with caching enabled:
   * </p>
   *
   * <pre>
   * mvn test -Dbcel.statistics=true -Dbcel.maxcached.size=100000 -Dbcel.maxcached=5000000
   * </pre>
   *
   * @see Constant
   */
  public final class ConstantUtf8 extends Constant {
  
      private static final class Cache {
  
          private static final boolean BCEL_STATISTICS = Boolean.getBoolean(SYS_PROP_STATISTICS);
          private static final int MAX_ENTRIES = Integer.getInteger(SYS_PROP_CACHE_MAX_ENTRIES, 0).intValue();
          private static final int INITIAL_CAPACITY = (int) (MAX_ENTRIES / 0.75);
  
          private static final HashMap<String, ConstantUtf8> CACHE = new LinkedHashMap<String, ConstantUtf8>(INITIAL_CAPACITY, 0.75f, true) {
  
              private static final long serialVersionUID = -8506975356158971766L;
  
              @Override
              protected boolean removeEldestEntry(final Map.Entry<String, ConstantUtf8> eldest) {
                  return size() > MAX_ENTRIES;
              }
          };
  
          // Set the size to 0 or below to skip caching entirely
          private static final int MAX_ENTRY_SIZE = Integer.getInteger(SYS_PROP_CACHE_MAX_ENTRY_SIZE, 200).intValue();
  
          static boolean isEnabled() {
              return MAX_ENTRIES > 0 && MAX_ENTRY_SIZE > 0;
          }
  
      }
  
      private static final Object LOCK = new Object();
      // TODO these should perhaps be AtomicInt?
      private static volatile int considered;
      private static volatile int created;
      private static volatile int hits;
      private static volatile int skipped;
  
      private static final String SYS_PROP_CACHE_MAX_ENTRIES = "bcel.maxcached";
      private static final String SYS_PROP_CACHE_MAX_ENTRY_SIZE = "bcel.maxcached.size";
      private static final String SYS_PROP_STATISTICS = "bcel.statistics";
  
      static {
          if (Cache.BCEL_STATISTICS) {
             Runtime.getRuntime().addShutdownHook(new Thread(ConstantUtf8::printStats));
         }
     }
 
     /**
      * Clears the cache.
      *
      * @since 6.4.0
      */
     public static void clearCache() {
         synchronized (LOCK) {
             Cache.CACHE.clear();
         }
     }
 
     // for access by test code
     static synchronized void clearStats() {
         hits = considered = skipped = created = 0;
     }
 
     // Avoid Spotbugs complaint about Write to static field
     private static synchronized void countCreated() {
         created++;
     }
 
     /**
      * Gets a new or cached instance of the given value.
      * <p>
      * See {@link ConstantUtf8} class Javadoc for details.
      * </p>
      *
      * @param value The value.
      * @return A new or cached instance of the given value.
      * @since 6.0
      */
     public static ConstantUtf8 getCachedInstance(final String value) {
         synchronized (LOCK) {
             if (value.length() > Cache.MAX_ENTRY_SIZE) {
                 skipped++;
                 return new ConstantUtf8(value);
             }
             considered++;
             synchronized (ConstantUtf8.class) { // might be better with a specific lock object
                 ConstantUtf8 result = Cache.CACHE.get(value);
                 if (result != null) {
                     hits++;
                     return result;
                 }
                 result = new ConstantUtf8(value);
                 Cache.CACHE.put(value, result);
                 return result;
             }
         }
     }
 
     /**
      * Gets a new or cached instance of the given value.
      * <p>
      * See {@link ConstantUtf8} class Javadoc for details.
      * </p>
      *
      * @param dataInput The value.
      * @return A new or cached instance of the given value.
      * @throws IOException Thrown if an I/O error occurs.
      * @since 6.0
      */
     public static ConstantUtf8 getInstance(final DataInput dataInput) throws IOException {
         return getInstance(dataInput.readUTF());
     }
 
     /**
      * Gets a new or cached instance of the given value.
      * <p>
      * See {@link ConstantUtf8} class Javadoc for details.
      * </p>
      *
      * @param value The value.
      * @return A new or cached instance of the given value.
      * @since 6.0
      */
     public static ConstantUtf8 getInstance(final String value) {
         return Cache.isEnabled() ? getCachedInstance(value) : new ConstantUtf8(value);
     }
 
     // for access by test code
     static void printStats() {
         final String prefix = "[Apache Commons BCEL]";
         System.err.printf("%s Cache hit %,d/%,d, %d skipped.%n", prefix, hits, considered, skipped);
         System.err.printf("%s Total of %,d ConstantUtf8 objects created.%n", prefix, created);
         System.err.printf("%s Configuration: %s=%,d, %s=%,d.%n", prefix, SYS_PROP_CACHE_MAX_ENTRIES, Cache.MAX_ENTRIES, SYS_PROP_CACHE_MAX_ENTRY_SIZE,
             Cache.MAX_ENTRY_SIZE);
     }
 
     private final String value;
 
     /**
      * Initializes from another object.
      *
      * @param constantUtf8 The value.
      */
     public ConstantUtf8(final ConstantUtf8 constantUtf8) {
         this(constantUtf8.getBytes());
     }
 
     /**
      * Initializes instance from file data.
      *
      * @param dataInput Input stream.
      * @throws IOException Thrown if an I/O error occurs.
      */
     ConstantUtf8(final DataInput dataInput) throws IOException {
         super(Const.CONSTANT_Utf8);
         value = dataInput.readUTF();
         countCreated();
     }
 
     /**
      * Constructs a ConstantUtf8.
      *
      * @param value Data.
      */
     public ConstantUtf8(final String value) {
         super(Const.CONSTANT_Utf8);
         this.value = Objects.requireNonNull(value, "value");
         countCreated();
     }
 
     /**
      * 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.visitConstantUtf8(this);
     }
 
     /**
      * Dumps String in Utf8 format to file stream.
      *
      * @param file Output file stream.
      * @throws IOException Thrown if an I/O error occurs.
      */
     @Override
     public void dump(final DataOutputStream file) throws IOException {
         file.writeByte(super.getTag());
         file.writeUTF(value);
     }
 
     /**
      * Gets the data converted to string.
      *
      * @return Data converted to string.
      */
     public String getBytes() {
         return value;
     }
 
     /**
      * @param bytes The raw bytes of this UTF-8.
      * @deprecated (since 6.0)
      */
     @java.lang.Deprecated
     public void setBytes(final String bytes) {
         throw new UnsupportedOperationException();
     }
 
     /**
      * @return String representation.
      */
     @Override
     public String toString() {
         return super.toString() + "(\"" + Utility.replace(value, "\n", "\\n") + "\")";
     }
 }