/*
 * 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 2012-8-2)
 */
package com.alibaba.cobar.parser.ast.expression;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

/**
 * an operator with arity of n<br/>
 * associative and commutative<br/>
 * non-polyadic operator with same precedence is not exist
 * 
 * @author <a href="mailto:shuo.qius@alibaba-inc.com">QIU Shuo</a>
 */
public abstract class PolyadicOperatorExpression extends AbstractExpression {
    protected List<Expression> operands;
    protected final int precedence;

    public PolyadicOperatorExpression(int precedence) {
        this(precedence, true);
    }

    public PolyadicOperatorExpression(int precedence, boolean leftCombine) {
        this(precedence, 4);
    }

    public PolyadicOperatorExpression(int precedence, int initArity) {
        this.precedence = precedence;
        this.operands = new ArrayList<Expression>(initArity);
    }

    /**
     * @return this
     */
    public PolyadicOperatorExpression appendOperand(Expression operand) {
        if (operand == null)
            return this;
        if (getClass().isAssignableFrom(operand.getClass())) {
            PolyadicOperatorExpression sub = (PolyadicOperatorExpression) operand;
            operands.addAll(sub.operands);
        } else {
            operands.add(operand);
        }
        return this;
    }

    /**
     * @param index start from 0
     */
    public Expression getOperand(int index) {
        if (index >= operands.size()) {
            throw new IllegalArgumentException("only contains " + operands.size() + " operands," + index
                    + " is out of bound");
        }
        return operands.get(index);
    }

    public int getArity() {
        return operands.size();
    }

    @Override
    public int getPrecedence() {
        return precedence;
    }

    public abstract String getOperator();

    @Override
    protected Object evaluationInternal(Map<? extends Object, ? extends Object> parameters) {
        return UNEVALUATABLE;
    }
}