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This is a plugin to Madura Objects. It provides a rules/constraint engine to assist with validation, deriving new values from user inputs (eg total of invoices entered on this customer) an manipulating metadata (eg because the amount is above X we make some field readonly). Note that the Java that is using the monitored objects is quite unaware of the rules layer implemented here. That means you can change rules without having to go back to your Java code, and it also means you don't have to wonder if everything implemented the same rules. Anything using that Java object has the rules (unless you turn them all off).

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/*******************************************************************************
 * Copyright (c)2014 Prometheus Consulting
 *
 * 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 nz.co.senanque.rulesparser;
import java.lang.reflect.Method;
import java.util.List;

import nz.co.senanque.rules.OperationsImpl;
import nz.co.senanque.rules.RuleSession;
import nz.co.senanque.rules.annotations.Function;
import nz.co.senanque.rules.annotations.InternalFunction;

import org.jdom.Document;
import org.jdom.Element;

/**
 * 
 * @author Roger Parkinson
 * @version $Revision: 1.4 $
 */

public final class FunctionDescriptorFactory
{
	public FunctionDescriptorFactory()
	{
	}
	
	@SuppressWarnings("unchecked")
	public void parse(Document doc, FunctionDescriptorHolder rtp)
	{
	    for (Element e: (List)doc.getRootElement().getChildren())
	    {
	        FunctionDescriptor fd = new FunctionDescriptor(e);
	        rtp.addFunction(fd);
	        if (fd.getOperator() != null)
	        {
	            rtp.addOperator(fd.getOperator(),fd);
	        }
	    }
	}
    public void loadOperators(FunctionDescriptorHolder rtp)
    {
        loadOperators(OperationsImpl.class,rtp);
        loadOperators(RuleSession.class,rtp);
        for (Class clazz: rtp.getExternalFunctionClasses())
        {
            loadExternalOperators(clazz,rtp);
        }
    }
    private void loadOperators(Class clazz, FunctionDescriptorHolder rtp)
    {
        for (Method method: clazz.getMethods())
        {
            InternalFunction function = method.getAnnotation(InternalFunction.class);
            if (function != null)
            {
                FunctionDescriptor fd = new FunctionDescriptor(method,function);
                rtp.addFunction(fd);
                if (fd.getOperator() != null)
                {
                    rtp.addOperator(fd.getOperator(),fd);
                }
            }
        }
    }
    private void loadExternalOperators(Class clazz, FunctionDescriptorHolder rtp)
    {
        for (Method method: clazz.getMethods())
        {
            Function function = method.getAnnotation(Function.class);
            if (function != null)
            {
                FunctionDescriptor fd = new FunctionDescriptor(method,function);
                rtp.addFunction(fd);
                if (fd.getOperator() != null)
                {
                    rtp.addOperator(fd.getOperator(),fd);
                }
            }
        }
    }
}