/* 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 java.net.URLConnection;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.zkoss.util.resource.Loader;

/**
 * A semi-implemented loader to used with {@link ResourceCaches#get}
 * to retrieve servlet resources.
 *
 * @author tomyeh
 */
public abstract class ResourceLoader<V> implements Loader<ResourceInfo, V> {
	private static final Logger log = LoggerFactory.getLogger(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 parameter passed from {@link ResourceCaches#get}.
	 */
	protected abstract 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 parameter passed from {@link ResourceCaches#get}.
	 */
	protected abstract 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) {
			URLConnection conn = null;
			try {
				conn = src.url.openConnection();
				final long v = conn.getLastModified();
				return v != -1 ? v : 0; //not to reload (5.0.6 for better performance)
			} catch (Throwable ex) {
				return -1; //reload (might be removed)
			} finally {
				if (conn != null) {
					try {
						conn.getInputStream().close();
					} catch (Throwable e) {
						log.warn("The connection cannot be closed", e);
					}
				}
			}
		}

		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);

		// Bug ZK-1132
		if (!src.file.exists() && src.extra != null
				&& ((ServletContextLocator) src.extra).getResourceAsStream(src.path) == null) {
			if (log.isDebugEnabled())
				log.debug("Not found: " + src.file);
			return null; //File not found
		}

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