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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.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.apache.commons.lang.StringUtils;

import nz.co.senanque.schemaparser.FieldDescriptor;

/**
 * Encapsulates a Rule abstract (real rules, formulae and constraints descend from this).
 * 
 * @author Roger Parkinson
 * @version $Revision: 1.4 $
 */
public abstract class AbstractRule implements Comparable
{
	private List m_conditions = new ArrayList();
	private List m_actions = new ArrayList();
    private String m_name;
    private String m_className;
    private String m_message;
    private String m_comment;
    private List m_messageArguments = new ArrayList();

    public AbstractRule()
	{
	}
	public abstract String toString();
	
	/**
	 * @see java.lang.Comparable#compareTo(Object)
	 * 
	 * We need this because we sort by the number of conditions on the rule
	 * The comparison is done in reverse because we want the high conditions at the top
	 */
	public final int compareTo(AbstractRule o)
	{
		Integer us = new Integer(this.getSpecificity());
		Integer them = new Integer(o.getSpecificity());
		return them.compareTo(us);
	}
	public final int getSpecificity()
	{
		return m_conditions.size();
	}
	protected final void addAction(Expression e)
	{
		m_actions.add(e);
	}
	protected final void addCondition(Expression e)
	{
		m_conditions.add(e);
	}
	public final String getName()
	{
		return m_name;
	}
	private final static String getList(String title, List list)
	{
		StringBuilder ret = new StringBuilder();
		for (Expression expression:list)
		{
            ret.append(title);
            ret.append(expression.toString());
            ret.append("    end\n");
		}
		return ret.toString();
	}
	public final String getActions()
	{
		return getList("    action\n",m_actions);
	}
	public final String getConditions()
	{
		return getList("    condition\n",m_conditions);
	}
    public String getClassName()
    {
        return m_className;
    }
    public void setClassName(String className)
    {
        m_className = className;
    }
    public String getMessage()
    {
        return m_message;
    }
    public void setMessage(String message)
    {
        m_message = message;
    }
    public void setName(String name)
    {
        m_name = name;
    }
    public Set getAllFieldsReferredTo()
    {
        Set ret = new HashSet();
        for (Expression expression: m_conditions)
        {
            ret.addAll(expression.getAllFieldsReferredTo());
        }
        for (Expression expression: m_actions)
        {
            ret.addAll(expression.getAllFieldsReferredTo());
        }
        ret.addAll(m_messageArguments);
        return ret;
    }
    public List getConditionList()
    {
        return m_conditions;
    }
    public List getActionList()
    {
        return m_actions;
    }
    public Set getAllFieldsRead()
    {
        Set ret = new HashSet();
        Set parameters = new HashSet();
        for (Expression expression: m_conditions)
        {
        	parameters.addAll(expression.getAllFieldsRead());
        }
        for (Expression expression: m_actions)
        {
        	parameters.addAll(expression.getAllFieldsRead());
        }
        for (Parameter parameter: parameters)
        {
        	FieldDescriptor fieldDescriptor = parameter.getFieldDescriptor();
        	if (!fieldDescriptor.getClazz().equals(m_className))
        	{
        		String parameterName = parameter.getValue();
        		String[] parameterNames = StringUtils.split(parameterName,".");
        		if (parameterNames != null)
        		{
        			parameterName = parameterNames[0];
        		}
        		FieldDescriptor fd = new FieldDescriptor(m_className,parameterName,m_className,parameter.isList());
        		ret.add(fd);
        	}
        	ret.add(fieldDescriptor);
        }
        return ret;
    }
    public void setComment(String comment)
    {
        m_comment = comment;
    }
    public String getComment()
    {
        return m_comment;
    }
    public void addMessageArgument(String operand, FieldDescriptor fieldDescriptor)
    {
        if (fieldDescriptor.isList())
        {
            throw new RuleParserException("List parameters in messages are not allowed");
        }
        Parameter parameter = new Parameter(operand,fieldDescriptor,false);
        m_messageArguments.add(parameter);
        
    }
    public List getMessageArguments()
    {
        return m_messageArguments;
    }
	public Set getAllFieldsOutput() {
		Set ret = new HashSet();
		for (Expression action: m_actions)
		{
			if (action.isAssign())
			{
				Parameter parameter = action.getAllFieldsReferredTo().iterator().next();
				if (parameter.isAssign())
				{
					ret.add(parameter.getFieldDescriptor());
				}
			}
		}
		return ret;
	}
	
	public String getDescription() {
		StringBuilder ret = new StringBuilder();
		if (m_message != null) {
			ret.append(m_message);
			if (m_name != null) {
				ret.append(" (");
				ret.append(m_name);
				ret.append(")");
			}
		} else if (m_name != null) {
			ret.append(m_name);
		} else {
			ret.append("");
		}
		return ret.toString();
	}

}