/*
    * Copyright (c) 2001-2017, Zoltan Farkas All Rights Reserved.
    *
    * This library is free software; you can redistribute it and/or
    * modify it under the terms of the GNU Lesser General Public
    * License as published by the Free Software Foundation; either
    * version 2.1 of the License, or (at your option) any later version.
    *
    * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
   *
   * Additionally licensed with:
   *
   * Licensed 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.spf4j.base;
  
  import java.lang.invoke.MethodHandle;
  import java.lang.invoke.MethodHandles;
  import java.lang.reflect.Constructor;
  import java.lang.reflect.Field;
  import java.security.AccessController;
  import java.security.PrivilegedAction;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  
  /**
   * Lower lever unsafe hacks for performance improvement.
   * These optimizations will work only up to including JDK 8.
   * @author Zoltan Farkas
   */
  public final class UnsafeString {
  
      /**
     * This field is byte[] in JDK11.
     */
    private static final MethodHandle CHARS_FIELD_GET;
  
    //String(char[] value, boolean share) {
    private static final MethodHandle PROTECTED_STR_CONSTR_HANDLE;
    private static final Class<?>[] PROTECTED_STR_CONSTR_PARAM_TYPES;
  
    static {
      Field charsField;
      charsField = AccessController.doPrivileged(new PrivilegedAction<Field>() {
        @Override
        public Field run() {
          Field charsField;
          try {
            charsField = String.class.getDeclaredField("value");
            Class<?> type = charsField.getType();
            if (type.isArray() && type.getComponentType() == char.class) {
              charsField.setAccessible(true);
            } else {
              Logger logger = Logger.getLogger(Strings.class.getName());
              logger.warning("char array stealing from String not supported");
              charsField = null;
            }
          } catch (NoSuchFieldException ex) {
            Logger logger = Logger.getLogger(Strings.class.getName());
            logger.warning("char array stealing from String not supported");
            logger.log(Level.FINEST, "Exception detail", ex);
            charsField = null;
          }
          return charsField;
        }
      });
      MethodHandles.Lookup lookup = MethodHandles.lookup();
      if (charsField != null && char[].class == charsField.getType()) {
        try {
          CHARS_FIELD_GET = lookup.unreflectGetter(charsField);
        } catch (IllegalAccessException ex) {
          throw new ExceptionInInitializerError(ex);
        }
      } else {
        CHARS_FIELD_GET = null;
      }
  
      // up until u45 String(int offset, int count, char value[]) {
      // u45 reverted to: String(char[] value, boolean share) {
      Constructor<String> prConstr = AccessController.doPrivileged(
              new PrivilegedAction<Constructor<String>>() {
        @Override
       public Constructor<String> run() {
         Constructor<String> constr;
         try {
           constr = String.class.getDeclaredConstructor(char[].class, boolean.class);
           constr.setAccessible(true);
         } catch (NoSuchMethodException ex) {
           try {
             constr = String.class.getDeclaredConstructor(int.class, int.class, char[].class);
             constr.setAccessible(true);
           } catch (NoSuchMethodException ex2) {
             ex2.addSuppressed(ex);
             Logger logger = Logger.getLogger(Strings.class.getName());
             logger.log(Level.FINE, "Building String from char[] without copy not supported");
             logger.log(Level.FINEST, "Exception detail", ex2);
             constr = null;
           }
         }
         return constr;
       }
     });
 
     if (prConstr == null) {
       PROTECTED_STR_CONSTR_PARAM_TYPES = null;
       PROTECTED_STR_CONSTR_HANDLE = null;
     } else {
       PROTECTED_STR_CONSTR_PARAM_TYPES = prConstr.getParameterTypes();
       try {
         PROTECTED_STR_CONSTR_HANDLE = lookup.unreflectConstructor(prConstr);
       } catch (IllegalAccessException ex) {
         throw new ExceptionInInitializerError(ex);
       }
     }
   }
 
 
 
   private UnsafeString() { }
 
   /**
    * Steal the underlying character array of a String.
    *
    * @param str
    * @return
    */
   public static char[] steal(final String str) {
     if (CHARS_FIELD_GET == null) {
       return str.toCharArray();
     } else {
       try {
         return (char[]) CHARS_FIELD_GET.invokeExact(str);
       } catch (Throwable ex) {
         UnknownError err = new UnknownError("Error while stealing String char array");
         err.addSuppressed(ex);
         throw err;
       }
     }
   }
 
    /**
    * Create a String based on the provided character array. No copy of the array is made.
    *
    * @param chars
    * @return
    */
   public static String wrap(final char[] chars) {
     if (PROTECTED_STR_CONSTR_PARAM_TYPES != null) {
       try {
         if (PROTECTED_STR_CONSTR_PARAM_TYPES.length == 3) {
           return (String) PROTECTED_STR_CONSTR_HANDLE.invokeExact(0, chars.length, chars);
         } else {
           return (String) PROTECTED_STR_CONSTR_HANDLE.invokeExact(chars, true);
         }
       } catch (Throwable ex) {
         UnknownError err = new UnknownError("Error while wrapping String char array");
         err.addSuppressed(ex);
         throw err;
       }
     } else {
       return new String(chars);
     }
   }
 
 }