content: /*
   * Copyright 1999-2012 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.
   */
  /**
   * (created at 2011-1-19)
   */
  package com.alibaba.cobar.parser.ast.expression.comparison;
  
  import java.util.Map;
  
  import com.alibaba.cobar.parser.ast.expression.BinaryOperatorExpression;
  import com.alibaba.cobar.parser.ast.expression.Expression;
  import com.alibaba.cobar.parser.ast.expression.ReplacableExpression;
  import com.alibaba.cobar.parser.ast.expression.primary.literal.LiteralBoolean;
  import com.alibaba.cobar.parser.util.ExprEvalUtils;
  import com.alibaba.cobar.parser.util.Pair;
  import com.alibaba.cobar.parser.visitor.SQLASTVisitor;
  
  /**
   * <code>higherPreExpr '<=>' higherPreExpr</code>
   * 
   * @author <a href="mailto:shuo.qius@alibaba-inc.com">QIU Shuo</a>
   */
  public class ComparisionNullSafeEqualsExpression extends BinaryOperatorExpression implements ReplacableExpression {
      public ComparisionNullSafeEqualsExpression(Expression leftOprand, Expression rightOprand) {
          super(leftOprand, rightOprand, PRECEDENCE_COMPARISION);
      }
  
      @Override
      public String getOperator() {
          return "<=>";
      }
  
      @Override
      public Object evaluationInternal(Map<? extends Object, ? extends Object> parameters) {
          Object left = leftOprand.evaluation(parameters);
          Object right = rightOprand.evaluation(parameters);
          if (left == UNEVALUATABLE || right == UNEVALUATABLE)
              return UNEVALUATABLE;
          if (left == null)
              return right == null ? LiteralBoolean.TRUE : LiteralBoolean.FALSE;
          if (right == null)
              return LiteralBoolean.FALSE;
          if (left instanceof Number || right instanceof Number) {
              Pair<Number, Number> pair = ExprEvalUtils.convertNum2SameLevel(left, right);
              left = pair.getKey();
              right = pair.getValue();
          }
          return left.equals(right) ? LiteralBoolean.TRUE : LiteralBoolean.FALSE;
      }
  
      private Expression replaceExpr;
  
      @Override
      public void setReplaceExpr(Expression replaceExpr) {
          this.replaceExpr = replaceExpr;
      }
  
      @Override
      public void clearReplaceExpr() {
          this.replaceExpr = null;
      }
  
      @Override
      public void accept(SQLASTVisitor visitor) {
          if (replaceExpr == null)
              visitor.visit(this);
          else
              replaceExpr.accept(visitor);
      }
  }
  