/*******************************************************************************
 * Copyright 2017 Graz University of Technology
 * EAAF-Core Components has been developed in a cooperation between EGIZ,  
 * A-SIT+, A-SIT, and Graz University of Technology.
 *
 * Licensed under the EUPL, Version 1.2 or - as soon they will be approved by
 * the European Commission - subsequent versions of the EUPL (the "Licence");
 * You may not use this work except in compliance with the Licence.
 * You may obtain a copy of the Licence at:
 * https://joinup.ec.europa.eu/news/understanding-eupl-v12
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the Licence is distributed on an "AS IS" basis,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the Licence for the specific language governing permissions and
 * limitations under the Licence.
 *
 * This product combines work with different licenses. See the "NOTICE" text
 * file for details on the various modules and licenses.
 * The "NOTICE" text file is part of the distribution. Any derivative works
 * that you distribute must include a readable copy of the "NOTICE" text file.
 *******************************************************************************/
/*******************************************************************************
 *******************************************************************************/
/*******************************************************************************
 *******************************************************************************/
package at.gv.egiz.eaaf.core.impl.idp.process.spring;

import java.util.Objects;

import javax.annotation.PostConstruct;

import org.apache.commons.lang3.BooleanUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.expression.BeanFactoryResolver;
import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;

import at.gv.egiz.eaaf.core.api.idp.process.ExpressionEvaluationContext;
import at.gv.egiz.eaaf.core.api.idp.process.ExpressionEvaluator;
import at.gv.egiz.eaaf.core.impl.idp.process.model.Transition;

/**
 * Expression evaluator for processing {@link Transition} conditions allowing to reference Spring beans from the
 * application context.
 * 
 * @author tknall
 * 
 */
public class SpringExpressionEvaluator implements ExpressionEvaluator {

	private Logger log = LoggerFactory.getLogger(getClass());
	private ExpressionParser parser = new SpelExpressionParser();
	private StandardEvaluationContext evaluationContext = new StandardEvaluationContext();

	@Autowired(required = false)
	private ApplicationContext ctx;

	@PostConstruct
	private void init() {
		if (ctx != null) {
			evaluationContext.setBeanResolver(new BeanFactoryResolver(ctx));
		}
	}

	@Override
	public boolean evaluate(ExpressionEvaluationContext expressionContext, String expression) {
		Objects.requireNonNull(expression, "Expression must not be null.");
		log.trace("Evaluating '{}'.", expression);

		Expression expr = parser.parseExpression(expression);
		Boolean result = expr.getValue(evaluationContext, expressionContext, Boolean.class);
		if (result == null) {
			log.warn("Evaluation of '{}' results in null-value.", expression);
		} else {
			log.debug("Expression '{}' -> {}", expression, result);
		}

		return BooleanUtils.isTrue(result);
	}

}