content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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.apache.ambari.server.api.predicate.expressions;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import org.apache.ambari.server.api.predicate.operators.Operator;
  
  /**
   * Base class for expressions.
   */
  public abstract class AbstractExpression<T> implements Expression<T> {
  
    /**
     * The operator.
     */
    private final Operator m_op;
  
    /**
     * The left operand.
     * */
    private T m_left = null;
  
    /**
     * The right operand.
     */
    private T m_right = null;
  
    /**
     * Constructor.
     *
     * @param op  the expressions operator
     */
    protected AbstractExpression(Operator op) {
      m_op = op;
    }
  
    @Override
    public void setLeftOperand(T left) {
      m_left = left;
    }
  
    @Override
    public void setRightOperand(T right) {
      m_right = right;
    }
  
    @Override
    public T getLeftOperand() {
      return m_left;
    }
  
    @Override
    public T getRightOperand() {
      return m_right;
    }
  
    @Override
    public Operator getOperator() {
      return m_op;
    }
  
    @Override
    public List<Expression> merge(Expression left, Expression right, int precedence) {
      return defaultMerge(left, right);
    }
  
    /**
     * Base merge implementation.
     * No merge is done, simply returns the left expression, this and the right expression.
     *
     * @param left   the expression to the left of this expression
     * @param right  the expression to the right of this expression
     *
     * @return a list containing the un-merged left expression, this and right expression
     */
    protected List<Expression> defaultMerge(Expression left, Expression right) {
      List<Expression> listExpressions = new ArrayList<>();
      if (left != null) {
        listExpressions.add(left);
      }
      listExpressions.add(this);
      if (right != null) {
        listExpressions.add(right);
      }
  
      return listExpressions;
    }
  }
  