/*
 * Copyright 2002-2013 the original author or authors.
 *
 * 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 org.springframework.expression.spel.ast;

import org.springframework.expression.EvaluationException;
import org.springframework.expression.TypedValue;
import org.springframework.expression.spel.ExpressionState;

/**
 * Represents the elvis operator ?:. For an expression "a?:b" if a is not null, the value
 * of the expression is "a", if a is null then the value of the expression is "b".
 *
 * @author Andy Clement
 * @since 3.0
 */
public class Elvis extends SpelNodeImpl {

	public Elvis(int pos, SpelNodeImpl... args) {
		super(pos,args);
	}


	/**
	 * Evaluate the condition and if not null, return it. If it is null return the other
	 * value.
	 * @param state the expression state
	 * @throws EvaluationException if the condition does not evaluate correctly to a
	 *         boolean or there is a problem executing the chosen alternative
	 */
	@Override
	public TypedValue getValueInternal(ExpressionState state) throws EvaluationException {
		TypedValue value = this.children[0].getValueInternal(state);
		if ((value.getValue() != null) && !((value.getValue() instanceof String) &&
				((String) value.getValue()).length() == 0)) {
			return value;
		}
		else {
			return this.children[1].getValueInternal(state);
		}
	}

	@Override
	public String toStringAST() {
		return new StringBuilder().append(getChild(0).toStringAST()).append(" ?: ").append(
				getChild(1).toStringAST()).toString();
	}

}
