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.List;
  
  import org.apache.ambari.server.api.predicate.InvalidQueryException;
  import org.apache.ambari.server.api.predicate.operators.Operator;
  import org.apache.ambari.server.controller.spi.Predicate;
  
  /**
   * Expression representation.
   * There are two types of expressions, relational and logical.
   * Each expression has an operator and either 2 operands for binary
   * expressions or 1 operand for unary expressions.
   */
  public interface Expression<T> {
  
    /**
     * Merge expression with surrounding expressions.
     *
     * @param left        the preceding expression
     * @param right       the following expression
     * @param precedence  the precedence level being merged.  Only expressions at this precedence level
     *                    should be merged. Others should simply return the left expression, themselves and
     *                    the right expression in that order.
     *
     * @return a list of expressions after merging.  Do not return any null elements.
     */
    List<Expression> merge(Expression left, Expression right, int precedence);
  
  
    /**
     * Get the predicate representation of the expression.
     * @return a predicate instance for the expression
     */
    Predicate toPredicate() throws InvalidQueryException;
  
    /**
     * Set the expressions left operand.
     *
     * @param left  the left operand
     */
    void setLeftOperand(T left);
  
    /**
     * Set the expressions right operand.
     *
     * @param right  the right operand
     */
    void setRightOperand(T right);
  
    /**
     * Get the left operand expression.
     *
     * @return the left operand
     */
    T getLeftOperand();
  
    /**
     * Get the right operand expression.
     *
     * @return the right operand.
     */
    T getRightOperand();
  
    /**
     * Get the expression operator.
     *
     * @return the logical operator for the expression
     */
    Operator getOperator();
  }
  