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JPMML class model evaluator
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/*
 * Copyright (c) 2014 Villu Ruusmann
 *
 * This file is part of JPMML-Evaluator
 *
 * JPMML-Evaluator is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * JPMML-Evaluator is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with JPMML-Evaluator.  If not, see .
 */
package org.jpmml.evaluator;

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Objects;

/**
 * 
 * A registry of Java user-defined functions (Java UDFs).
 * 
 */
public class FunctionRegistry {

	private FunctionRegistry(){
	}

	/**
	 * 
	 * Gets a function for a name.
	 * 

	 *
	 * 

	 * First, if the name is registered with a singleton function instance, returns that instance.
	 * After that, if the name represents a {@link Function} class on the application classpath, loads it, and returns a newly created instance.
	 * 
	 */
	static
	public Function getFunction(String name){

		if(name == null){
			return null;
		} // End if

		if(FunctionRegistry.functions.containsKey(name)){
			Function function = FunctionRegistry.functions.get(name);

			return function;
		}

		Class functionClazz;

		if(FunctionRegistry.functionClazzes.containsKey(name)){
			functionClazz = FunctionRegistry.functionClazzes.get(name);
		} else

		{
			functionClazz = loadFunctionClass(name);

			FunctionRegistry.functionClazzes.put(name, functionClazz);
		} // End if

		if(functionClazz != null){
			Function function;

			try {
				function = (Function)functionClazz.newInstance();
			} catch(IllegalAccessException | InstantiationException | ExceptionInInitializerError e){
				throw (EvaluationException)new EvaluationException()
					.initCause(e);
			}

			return function;
		}

		return null;
	}

	/**
	 * 
	 * Registers a function by its default name.
	 * 
	 */
	static
	public void putFunction(Function function){
		putFunction(function.getName(), function);
	}

	/**
	 * 
	 * Registers a function by a name other than its default name.
	 * 
	 */
	static
	public void putFunction(String name, Function function){
		FunctionRegistry.functions.put(Objects.requireNonNull(name), function);
	}

	/**
	 * 
	 * Registers a function class.
	 * 
	 */
	static
	public void putFunction(String name, Class functionClazz){
		FunctionRegistry.functionClazzes.put(Objects.requireNonNull(name), checkClass(functionClazz));
	}

	static
	public void removeFunction(String name){
		FunctionRegistry.functions.remove(name);
		FunctionRegistry.functionClazzes.remove(name);
	}

	static
	private Class loadFunctionClass(String name){
		Class clazz;

		try {
			ClassLoader classLoader = (Thread.currentThread()).getContextClassLoader();

			if(classLoader == null){
				classLoader = (FunctionRegistry.class).getClassLoader();
			}

			clazz = classLoader.loadClass(name);
		} catch(ClassNotFoundException cnfe){
			return null;
		}

		return checkClass(clazz);
	}

	static
	private Class checkClass(Class clazz){

		if(!(Function.class).isAssignableFrom(clazz)){
			throw new TypeCheckException(Function.class, clazz);
		}

		return clazz;
	}

	private static final Map functions = new LinkedHashMap<>();

	private static final Map> functionClazzes = new LinkedHashMap<>();
}