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/* 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.activiti.engine.impl.el;

import java.util.Map;
import javax.el.ELContext;
import javax.el.MethodNotFoundException;
import javax.el.PropertyNotFoundException;
import javax.el.ValueExpression;
import org.activiti.engine.ActivitiException;
import org.activiti.engine.delegate.Expression;
import org.activiti.engine.delegate.VariableScope;
import org.activiti.engine.impl.context.Context;
import org.activiti.engine.impl.delegate.invocation.ExpressionGetInvocation;
import org.activiti.engine.impl.delegate.invocation.ExpressionSetInvocation;
import org.activiti.engine.impl.interceptor.DelegateInterceptor;

/**
 * Expression implementation backed by a JUEL {@link ValueExpression}.
 *


 */
public class JuelExpression implements Expression {

    private String expressionText;
    private ValueExpression valueExpression;

    public JuelExpression(ValueExpression valueExpression, String expressionText) {
        this.valueExpression = valueExpression;
        this.expressionText = expressionText;
    }

    @Override
    public Object getValue(VariableScope variableScope) {
        ELContext elContext = Context.getProcessEngineConfiguration()
                                     .getExpressionManager()
                                     .getElContext(variableScope);
        return getValueFromContext(elContext, Context.getProcessEngineConfiguration().getDelegateInterceptor());
    }

    @Override
    public void setValue(Object value, VariableScope variableScope) {
        ELContext elContext = Context.getProcessEngineConfiguration()
                                     .getExpressionManager()
                                     .getElContext(variableScope);
        try {
            ExpressionSetInvocation invocation = new ExpressionSetInvocation(valueExpression, elContext, value);
            Context.getProcessEngineConfiguration().getDelegateInterceptor().handleInvocation(invocation);
        } catch (Exception e) {
            throw new ActivitiException("Error while evaluating expression: " + expressionText, e);
        }
    }

    @Override
    public String toString() {
        if (valueExpression != null) {
            return valueExpression.getExpressionString();
        }
        return super.toString();
    }

    @Override
    public String getExpressionText() {
        return expressionText;
    }

    @Override
    public Object getValue(ExpressionManager expressionManager,
        DelegateInterceptor delegateInterceptor, Map availableVariables) {
        ELContext elContext = expressionManager.getElContext(availableVariables);
        return getValueFromContext(elContext, delegateInterceptor);
    }

    private Object getValueFromContext(ELContext elContext,
        DelegateInterceptor delegateInterceptor) {
        try {
            ExpressionGetInvocation invocation = new ExpressionGetInvocation(valueExpression, elContext);
            delegateInterceptor.handleInvocation(invocation);
            return invocation.getInvocationResult();
        } catch (PropertyNotFoundException pnfe) {
            throw new ActivitiException("Unknown property used in expression: " + expressionText, pnfe);
        } catch (MethodNotFoundException mnfe) {
            throw new ActivitiException("Unknown method used in expression: " + expressionText, mnfe);
        } catch (Exception ele) {
            throw new ActivitiException("Error while evaluating expression: " + expressionText, ele);
        }
    }
}