content: /*
   * Copyright 1999-2017 Alibaba Group.
   *
   * 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 com.alibaba.fastjson.parser;
  
  import com.alibaba.fastjson.JSON;
  
  /**
   * @author wenshao[szujobs@hotmail.com]
   */
  public class SymbolTable {
  
      private final String[] symbols;
      private final int      indexMask;
      
      public SymbolTable(int tableSize){
          this.indexMask = tableSize - 1;
          this.symbols = new String[tableSize];
          
          this.addSymbol("$ref", 0, 4, "$ref".hashCode());
          this.addSymbol(JSON.DEFAULT_TYPE_KEY, 0, JSON.DEFAULT_TYPE_KEY.length(), JSON.DEFAULT_TYPE_KEY.hashCode());
      }
  
      public String addSymbol(char[] buffer, int offset, int len) {
          // search for identical symbol
          int hash = hash(buffer, offset, len);
          return addSymbol(buffer, offset, len, hash);
      }
  
      /**
       * Adds the specified symbol to the symbol table and returns a reference to the unique symbol. If the symbol already
       * exists, the previous symbol reference is returned instead, in order guarantee that symbol references remain
       * unique.
       * 
       * @param buffer The buffer containing the new symbol.
       * @param offset The offset into the buffer of the new symbol.
       * @param len The length of the new symbol in the buffer.
       */
      public String addSymbol(char[] buffer, int offset, int len, int hash) {
          final int bucket = hash & indexMask;
          
          String symbol = symbols[bucket];
          if (symbol != null) {
              boolean eq = true;
              if (hash == symbol.hashCode() // 
                      && len == symbol.length()) {
                  for (int i = 0; i < len; i++) {
                      if (buffer[offset + i] != symbol.charAt(i)) {
                          eq = false;
                          break;
                      }
                  }
              } else {
                  eq = false;
              }
              
              if (eq) {
                  return symbol;
              } else {
                  return new String(buffer, offset, len);    
              }
          }
          
          symbol = new String(buffer, offset, len).intern();
          symbols[bucket] = symbol;
          return symbol;
      }
  
      public String addSymbol(String buffer, int offset, int len, int hash) {
          return addSymbol(buffer, offset, len, hash, false);
      }
  
      public String addSymbol(String buffer, int offset, int len, int hash, boolean replace) {
          final int bucket = hash & indexMask;
  
          String symbol = symbols[bucket];
          if (symbol != null) {
              if (hash == symbol.hashCode() // 
                      && len == symbol.length() //
                      && buffer.startsWith(symbol, offset)) {
                  return symbol;
              }
  
              String str = subString(buffer, offset, len);
  
              if (replace) {
                  symbols[bucket] = str;
              }
  
              return str;
          }
          
          symbol = len == buffer.length() //
              ? buffer //
              : subString(buffer, offset, len);
          symbol = symbol.intern();
          symbols[bucket] = symbol;
          return symbol;
      }
      
      private static String subString(String src, int offset, int len) {
          char[] chars = new char[len];
          src.getChars(offset, offset + len, chars, 0);
          return new String(chars);
      }
  
      public static int hash(char[] buffer, int offset, int len) {
          int h = 0;
          int off = offset;
  
          for (int i = 0; i < len; i++) {
              h = 31 * h + buffer[off++];
          }
          return h;
      }
  }