/* ResourceLoader.java

	Purpose:
		
	Description:
		
	History:
		Tue Aug 30 18:31:26     2005, Created by tomyeh

Copyright (C) 2005 Potix Corporation. All Rights Reserved.

{{IS_RIGHT
	This program is distributed under LGPL Version 2.1 in the hope that
	it will be useful, but WITHOUT ANY WARRANTY.
}}IS_RIGHT
*/
package org.zkoss.web.util.resource;

import java.io.File;
import java.io.FileNotFoundException;
import java.net.URL;

import javax.servlet.ServletContext;

import org.zkoss.util.resource.Loader;
import org.zkoss.util.logging.Log;

/**
 * A semi-implemented loader to used with {@link ResourceCaches#get}
 * to retrieve servlet resources.
 *
 * @author tomyeh
 */
abstract public class ResourceLoader<V> implements Loader<ResourceInfo, V> {
	private static final Log log = Log.lookup(ResourceLoader.class);

	protected ResourceLoader() {
	}

	/** Parses the specified file and returns the result which
	 * will be stored into the cache ({@link ResourceCaches#get}).
	 *
	 * <p>Deriving must override this method.
	 *
	 * @param extra the extra paramter passed from {@link ResourceCaches#get}.
	 */
	abstract protected V parse(String path, File file, Object extra)
	throws Exception;
	/** Parses the specified URL and returns the result which
	 * will be stored into the cache ({@link ResourceCaches#get}).
	 *
	 * <p>Deriving must override this method.
	 *
	 * @param extra the extra paramter passed from {@link ResourceCaches#get}.
	 */
	abstract protected V parse(String path, URL url, Object extra)
	throws Exception;

	public boolean shallCheck(ResourceInfo src, long expiredMillis) {
		return expiredMillis > 0;
		//FUTURE: prolong if src.url's protocol is http, https or ftp
	}
	public long getLastModified(ResourceInfo src) {
		if (src.url != null) {
			try {
				final long v = src.url.openConnection().getLastModified();
				return v != -1 ? v: 0; //not to reload (5.0.6 for better performance)
			} catch (Throwable ex) {
				return -1; //reload (might be removed)
			}
		}

		final long v = src.file.lastModified();
		return v == -1 ? 0: //not to reload if unknown (5.0.6 for better performance)
			v == 0 ? -1: v; //0 means nonexistent so reload
	}
	public V load(ResourceInfo src) throws Exception {
		if (src.url != null)
			return parse(src.path, src.url, src.extra);
		//PATCH: IT MIGHT BE A web-fragment RESOURCE. IN THIS CASE THE FILE WON'T EXIST 
		//BUT IT'S CONTENT CAN STILL BE RETRIEVED AS A BYTE-STREAM
//System.out.println("AKI2");
		if (!src.file.exists() && ((ServletContextLocator) src.extra).getResourceAsStream(src.path) == null) {
			if (log.debugable()) log.debug("Not found: "+src.file);
			return null; //File not found
		}

		if (log.debugable()) log.debug("Loading "+src.file);
		try {
			return parse(src.path, src.file, src.extra);
		} catch (FileNotFoundException ex) {
			return null;
		}
	}
}