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/*
 * Copyright 2014 the original author or authors.
 *
 * 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 leap.lang.el;

import java.util.Map;
import java.util.WeakHashMap;

import leap.lang.Args;
import leap.lang.reflect.ReflectField;

public class ElConstantField implements ElProperty {
	
	private static final Object lock = new Object();
	private static final Map, Map> constants = 
			new WeakHashMap, Map>();
	
	public static ElConstantField of(ReflectField field) {
		if(!field.isFinal()){
			return null;
		}
		
		Class cls = field.getDeclaringClass();
		String   name = field.getName();

		synchronized (lock) {
			Map cache = constants.get(cls);
			
			if(null == cache){
				cache = new WeakHashMap();
				constants.put(cls, cache);
			}
			
			ElConstantField f = cache.get(name);
			if(null == f){
				f = new ElConstantField(field);
				cache.put(name, f);
			}
			
			return f;
        }
	}

	private final Object value;

	private ElConstantField(ReflectField field) {
		Args.assertTrue(field.isStatic() && field.isFinal(),"Must be static final field");
		this.value = field.getValue(null);
	}
	
	@Override
	public Object getValue(ElEvalContext context, Object instance) throws Throwable {
		return value;
	}
}