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package com.buabook.spring.properties;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.beans.factory.support.AbstractBeanFactory;

import com.google.common.base.Strings;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;

/**
 * Spring Properties Programmatic Access
 * Provides programmatic access to the Spring properties defined in the application.
 * NOTE: By default, this class caches results indefinitely once queried from the property file. Override
 * {@link #buildNewCache()} if you wish to change this behaviour.
 * (c) 2015 Sport Trades Ltd
 * 
 * @author Jas Rajasansir
 * @version 1.0.0
 * @since 6 Oct 2015
 */
public class PropertyLoader {
	private final AbstractBeanFactory beanFactory;
	
	private final LoadingCache cache;

	
	/** @see PropertyLoader */
	public PropertyLoader(AbstractBeanFactory beanFactory) {
		this.beanFactory = beanFactory;
		this.cache = buildNewCache();
	}
	
	/** 
	 * NOTE: It is recommended in most cases to use Spring's {@link Value} annotation to load
	 * property configuration. This method is supplied in the rare cases that you need to programmatically 
	 * define the key.
	 * @param property The property name to load, without the Spring ${ and } tags (these
	 * will be added automatically)
	 * @return The specified property value
	 */
	public String getProperty(String property) {
		if(Strings.isNullOrEmpty(property))
			return null;
		
		return cache.getUnchecked(property);
	}
	
	
	/** 
	 * Provides the cache to store properties loaded via the {@link AbstractBeanFactory}.
	 * This can be overridden if necessary to customise the cache. Use {@link #getCacheLoader()} as the {@link CacheLoader}.
	 * @see CacheBuilder
	 */
	protected LoadingCache buildNewCache() {
		return CacheBuilder.newBuilder().build(getCacheLoader());
	}
	
	
	private String getPropertyFromSpring(String property) {
		String propertyName = "${" + property + "}";
		String propertyValue = "";
		
		try {
			propertyValue = beanFactory.resolveEmbeddedValue(propertyName);
		} catch(IllegalArgumentException e) {
			// If the property doesn't exist, an IllegalArgumentException will be thrown. We'll catch it and just return empty string
		}
		
		return propertyValue;
	}
	
	private CacheLoader getCacheLoader() {
		return new CacheLoader() {
			@Override
			public String load(String key) throws Exception {
				return getPropertyFromSpring(key);
			}
		};
	}
}