/*
    * Copyright 2002-2011 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 org.springframework.core.io;
  
  import java.io.File;
  import java.io.IOException;
  import java.io.InputStream;
  import java.net.HttpURLConnection;
  import java.net.URI;
  import java.net.URL;
  import java.net.URLConnection;
  
  import org.springframework.util.ResourceUtils;
  
  /**
   * Abstract base class for resources which resolve URLs into File references,
   * such as {@link UrlResource} or {@link ClassPathResource}.
   *
   * <p>Detects the "file" protocol as well as the JBoss "vfs" protocol in URLs,
   * resolving file system references accordingly.
   *
   * @author Juergen Hoeller
   * @since 3.0
   */
  public abstract class AbstractFileResolvingResource extends AbstractResource {
  
  	/**
  	 * This implementation returns a File reference for the underlying class path
  	 * resource, provided that it refers to a file in the file system.
  	 * @see org.springframework.util.ResourceUtils#getFile(java.net.URL, String)
  	 */
  	@Override
  	public File getFile() throws IOException {
  		URL url = getURL();
  		if (url.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
  			return VfsResourceDelegate.getResource(url).getFile();
  		}
  		return ResourceUtils.getFile(url, getDescription());
  	}
  
  	/**
  	 * This implementation determines the underlying File
  	 * (or jar file, in case of a resource in a jar/zip).
  	 */
  	@Override
  	protected File getFileForLastModifiedCheck() throws IOException {
  		URL url = getURL();
  		if (ResourceUtils.isJarURL(url)) {
  			URL actualUrl = ResourceUtils.extractJarFileURL(url);
  			if (actualUrl.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
  				return VfsResourceDelegate.getResource(actualUrl).getFile();
  			}
  			return ResourceUtils.getFile(actualUrl, "Jar URL");
  		}
  		else {
  			return getFile();
  		}
  	}
  
  	/**
  	 * This implementation returns a File reference for the underlying class path
  	 * resource, provided that it refers to a file in the file system.
  	 * @see org.springframework.util.ResourceUtils#getFile(java.net.URI, String)
  	 */
  	protected File getFile(URI uri) throws IOException {
  		if (uri.getScheme().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
  			return VfsResourceDelegate.getResource(uri).getFile();
  		}
  		return ResourceUtils.getFile(uri, getDescription());
  	}
  
  
  	@Override
  	public boolean exists() {
  		try {
  			URL url = getURL();
  			if (ResourceUtils.isFileURL(url)) {
  				// Proceed with file system resolution...
  				return getFile().exists();
  			}
  			else {
  				// Try a URL connection content-length header...
  				URLConnection con = url.openConnection();
  				ResourceUtils.useCachesIfNecessary(con);
  				HttpURLConnection httpCon =
 						(con instanceof HttpURLConnection ? (HttpURLConnection) con : null);
 				if (httpCon != null) {
 					httpCon.setRequestMethod("HEAD");
 					int code = httpCon.getResponseCode();
 					if (code == HttpURLConnection.HTTP_OK) {
 						return true;
 					}
 					else if (code == HttpURLConnection.HTTP_NOT_FOUND) {
 						return false;
 					}
 				}
 				if (con.getContentLength() >= 0) {
 					return true;
 				}
 				if (httpCon != null) {
 					// no HTTP OK status, and no content-length header: give up
 					httpCon.disconnect();
 					return false;
 				}
 				else {
 					// Fall back to stream existence: can we open the stream?
 					InputStream is = getInputStream();
 					is.close();
 					return true;
 				}
 			}
 		}
 		catch (IOException ex) {
 			return false;
 		}
 	}
 
 	@Override
 	public boolean isReadable() {
 		try {
 			URL url = getURL();
 			if (ResourceUtils.isFileURL(url)) {
 				// Proceed with file system resolution...
 				File file = getFile();
 				return (file.canRead() && !file.isDirectory());
 			}
 			else {
 				return true;
 			}
 		}
 		catch (IOException ex) {
 			return false;
 		}
 	}
 
 	@Override
 	public long contentLength() throws IOException {
 		URL url = getURL();
 		if (ResourceUtils.isFileURL(url)) {
 			// Proceed with file system resolution...
 			return getFile().length();
 		}
 		else {
 			// Try a URL connection content-length header...
 			URLConnection con = url.openConnection();
 			ResourceUtils.useCachesIfNecessary(con);
 			if (con instanceof HttpURLConnection) {
 				((HttpURLConnection) con).setRequestMethod("HEAD");
 			}
 			return con.getContentLength();
 		}
 	}
 
 	@Override
 	public long lastModified() throws IOException {
 		URL url = getURL();
 		if (ResourceUtils.isFileURL(url) || ResourceUtils.isJarURL(url)) {
 			// Proceed with file system resolution...
 			return super.lastModified();
 		}
 		else {
 			// Try a URL connection last-modified header...
 			URLConnection con = url.openConnection();
 			ResourceUtils.useCachesIfNecessary(con);
 			if (con instanceof HttpURLConnection) {
 				((HttpURLConnection) con).setRequestMethod("HEAD");
 			}
 			return con.getLastModified();
 		}
 	}
 
 
 	/**
 	 * Inner delegate class, avoiding a hard JBoss VFS API dependency at runtime.
 	 */
 	private static class VfsResourceDelegate {
 
 		public static Resource getResource(URL url) throws IOException {
 			return new VfsResource(VfsUtils.getRoot(url));
 		}
 
 		public static Resource getResource(URI uri) throws IOException {
 			return new VfsResource(VfsUtils.getRoot(uri));
 		}
 	}
 
 }