content: /*
   * Copyright 1999-2017 Alibaba Group Holding Ltd.
   *
   * 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.druid.sql.parser;
  
  import com.alibaba.druid.DbType;
  import com.alibaba.druid.sql.ast.statement.SQLSelectQueryBlock;
  import com.alibaba.druid.support.logging.Log;
  import com.alibaba.druid.support.logging.LogFactory;
  import com.alibaba.druid.util.FnvHash;
  
  import java.util.List;
  import java.util.concurrent.CopyOnWriteArrayList;
  
  public class SQLSelectListCache {
      private static final Log LOG = LogFactory.getLog(SQLSelectListCache.class);
      private final DbType dbType;
      private final List<Entry> entries = new CopyOnWriteArrayList<Entry>();
  
      public SQLSelectListCache(DbType dbType) {
          this.dbType = dbType;
      }
  
      public void add(String select) {
          if (select == null || select.length() == 0) {
              return;
          }
  
          SQLSelectParser selectParser = SQLParserUtils.createSQLStatementParser(select, dbType)
                  .createSQLSelectParser();
          SQLSelectQueryBlock queryBlock = SQLParserUtils.createSelectQueryBlock(dbType);
          selectParser.accept(Token.SELECT);
  
          selectParser.parseSelectList(queryBlock);
  
          selectParser.accept(Token.FROM);
          selectParser.accept(Token.EOF);
  
          String printSql = queryBlock.toString();
          long printSqlHash = FnvHash.fnv1a_64_lower(printSql);
          entries.add(
                  new Entry(
                          select.substring(6),
                          queryBlock,
                          printSql,
                          printSqlHash
                  )
          );
  
          if (entries.size() > 5) {
              LOG.warn("SelectListCache is too large.");
          }
      }
  
      public int getSize() {
          return entries.size();
      }
  
      public void clear() {
          entries.clear();
      }
  
      public boolean match(Lexer lexer, SQLSelectQueryBlock queryBlock) {
          if (lexer.token != Token.SELECT) {
              return false;
          }
  
          int pos = lexer.pos;
          String text = lexer.text;
  
          for (int i = 0; i < entries.size(); i++) {
              Entry entry = entries.get(i);
              String block = entry.sql;
              if (text.startsWith(block, pos)) {
                  //SQLSelectQueryBlock queryBlockCached = queryBlockCache.get(i);
                  // queryBlockCached.cloneSelectListTo(queryBlock);
                  queryBlock.setCachedSelectList(entry.printSql, entry.printSqlHash);
  
                  int len = pos + block.length();
                  //todo fix reset
                  lexer.reset(len, text.charAt(len), Token.FROM);
                  return true;
              }
          }
          return false;
      }
  
      private static class Entry {
          public final String sql;
          public final SQLSelectQueryBlock queryBlock;
          public final String printSql;
          public final long printSqlHash;
  
          public Entry(String sql, SQLSelectQueryBlock queryBlock, String printSql, long printSqlHash) {
              this.sql = sql;
              this.queryBlock = queryBlock;
              this.printSql = printSql;
              this.printSqlHash = printSqlHash;
          }
      }
  }
  