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.visitor.functions;
  
  import com.alibaba.druid.sql.ast.SQLExpr;
  import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
  import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
  
  import java.util.Calendar;
  import java.util.Date;
  import java.util.List;
  
  import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_ERROR;
  import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
  
  public class DateAdd implements Function {
      public static final DateAdd instance = new DateAdd();
  
      public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
          final List<SQLExpr> arguments = x.getArguments();
          if (arguments.size() != 3) {
              return EVAL_ERROR;
          }
  
          for (SQLExpr arg : arguments) {
              arg.accept(visitor);
          }
  
          Object v0 = arguments.get(0).getAttributes().get(EVAL_VALUE);
          Object v1 = arguments.get(1).getAttributes().get(EVAL_VALUE);
          Object v2 = arguments.get(2).getAttributes().get(EVAL_VALUE);
  
          if (v0 instanceof Date
                  && v1 instanceof Integer
                  && v2 instanceof String) {
              Date date = (Date) v0;
              int delta = ((Integer) v1);
  
              if ("day".equalsIgnoreCase((String) v2)) {
                  Calendar calendar = Calendar.getInstance();
                  calendar.setTime(date);
                  calendar.add(Calendar.DAY_OF_MONTH, delta);
  
                  return calendar.getTime();
              }
  
          }
  
          SQLExpr arg = arguments.get(0);
          arg.accept(visitor);
          Object itemValue = arg.getAttributes().get(EVAL_VALUE);
          if (itemValue == null) {
              return null;
          }
  
          return null;
      }
  }
  