/*
    * Copyright (C) 2009-2010, Google Inc.
    * and other copyright owners as documented in the project's IP log.
    *
    * This program and the accompanying materials are made available
    * under the terms of the Eclipse Distribution License v1.0 which
    * accompanies this distribution, is reproduced below, and is
    * available at http://www.eclipse.org/org/documents/edl-v10.php
    *
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   * without modification, are permitted provided that the following
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   *   notice, this list of conditions and the following disclaimer.
   *
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   * - Neither the name of the Eclipse Foundation, Inc. nor the
   *   names of its contributors may be used to endorse or promote
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   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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  package org.eclipse.jgit.http.server.glue;
  
  import java.io.IOException;
  import java.util.Enumeration;
  import java.util.NoSuchElementException;
  import java.util.Set;
  
  import javax.servlet.Filter;
  import javax.servlet.FilterChain;
  import javax.servlet.ServletConfig;
  import javax.servlet.ServletContext;
  import javax.servlet.ServletException;
  import javax.servlet.ServletRequest;
  import javax.servlet.ServletResponse;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  /**
   * Encapsulates the entire serving stack for a single URL.
   * <p>
   * Subclasses provide the implementation of {@link #match(HttpServletRequest)},
   * which is called by {@link MetaServlet} in registration order to determine the
   * pipeline that will be used to handle a request.
   * <p>
   * The very bottom of each pipeline is a single {@link HttpServlet} that will
   * handle producing the response for this pipeline's URL. {@link Filter}s may
   * also be registered and applied around the servlet's processing, to manage
   * request attributes, set standard response headers, or completely override the
   * response generation.
   */
  abstract class UrlPipeline {
  	/** Filters to apply around {@link #servlet}; may be empty but never null. */
  	private final Filter[] filters;
  
  	/** Instance that must generate the response; never null. */
  	private final HttpServlet servlet;
  
  	UrlPipeline(final Filter[] filters, final HttpServlet servlet) {
  		this.filters = filters;
  		this.servlet = servlet;
  	}
  
  	/**
  	 * Initialize all contained filters and servlets.
  	 *
  	 * @param context
  	 *            the servlet container context our {@link MetaServlet} is
  	 *            running within.
  	 * @param inited
  	 *            <i>(input/output)</i> the set of filters and servlets which
  	 *            have already been initialized within the container context. If
  	 *            those same instances appear in this pipeline they are not
  	 *            initialized a second time. Filters and servlets that are first
  	 *            initialized by this pipeline will be added to this set.
  	 * @throws ServletException
 	 *             a filter or servlet is unable to initialize.
 	 */
 	void init(final ServletContext context, final Set<Object> inited)
 			throws ServletException {
 		for (Filter ref : filters)
 			initFilter(ref, context, inited);
 		initServlet(servlet, context, inited);
 	}
 
 	private static void initFilter(final Filter ref,
 			final ServletContext context, final Set<Object> inited)
 			throws ServletException {
 		if (!inited.contains(ref)) {
 			ref.init(new NoParameterFilterConfig(ref.getClass().getName(),
 					context));
 			inited.add(ref);
 		}
 	}
 
 	private static void initServlet(final HttpServlet ref,
 			final ServletContext context, final Set<Object> inited)
 			throws ServletException {
 		if (!inited.contains(ref)) {
 			ref.init(new ServletConfig() {
 				public String getInitParameter(String name) {
 					return null;
 				}
 
 				public Enumeration<String> getInitParameterNames() {
 					return new Enumeration<String>() {
 						public boolean hasMoreElements() {
 							return false;
 						}
 
 						public String nextElement() {
 							throw new NoSuchElementException();
 						}
 					};
 				}
 
 				public ServletContext getServletContext() {
 					return context;
 				}
 
 				public String getServletName() {
 					return ref.getClass().getName();
 				}
 			});
 			inited.add(ref);
 		}
 	}
 
 	/**
 	 * Destroy all contained filters and servlets.
 	 *
 	 * @param destroyed
 	 *            <i>(input/output)</i> the set of filters and servlets which
 	 *            have already been destroyed within the container context. If
 	 *            those same instances appear in this pipeline they are not
 	 *            destroyed a second time. Filters and servlets that are first
 	 *            destroyed by this pipeline will be added to this set.
 	 */
 	void destroy(final Set<Object> destroyed) {
 		for (Filter ref : filters)
 			destroyFilter(ref, destroyed);
 		destroyServlet(servlet, destroyed);
 	}
 
 	private static void destroyFilter(Filter ref, Set<Object> destroyed) {
 		if (!destroyed.contains(ref)) {
 			ref.destroy();
 			destroyed.add(ref);
 		}
 	}
 
 	private static void destroyServlet(HttpServlet ref, Set<Object> destroyed) {
 		if (!destroyed.contains(ref)) {
 			ref.destroy();
 			destroyed.add(ref);
 		}
 	}
 
 	/**
 	 * Determine if this pipeline handles the request's URL.
 	 * <p>
 	 * This method should match on the request's {@code getPathInfo()} method,
 	 * as {@link MetaServlet} passes the request along as-is to each pipeline's
 	 * match method.
 	 *
 	 * @param req
 	 *            current HTTP request being considered by {@link MetaServlet}.
 	 * @return {@code true} if this pipeline is configured to handle the
 	 *         request; {@code false} otherwise.
 	 */
 	abstract boolean match(HttpServletRequest req);
 
 	/**
 	 * Execute the filters and the servlet on the request.
 	 * <p>
 	 * Invoked by {@link MetaServlet} once {@link #match(HttpServletRequest)}
 	 * has determined this pipeline is the correct pipeline to handle the
 	 * current request.
 	 *
 	 * @param req
 	 *            current HTTP request.
 	 * @param rsp
 	 *            current HTTP response.
 	 * @throws ServletException
 	 *             request cannot be completed.
 	 * @throws IOException
 	 *             IO error prevents the request from being completed.
 	 */
 	void service(HttpServletRequest req, HttpServletResponse rsp)
 			throws ServletException, IOException {
 		if (0 < filters.length)
 			new Chain(filters, servlet).doFilter(req, rsp);
 		else
 			servlet.service(req, rsp);
 	}
 
 	private static class Chain implements FilterChain {
 		private final Filter[] filters;
 
 		private final HttpServlet servlet;
 
 		private int filterIdx;
 
 		Chain(final Filter[] filters, final HttpServlet servlet) {
 			this.filters = filters;
 			this.servlet = servlet;
 		}
 
 		public void doFilter(ServletRequest req, ServletResponse rsp)
 				throws IOException, ServletException {
 			if (filterIdx < filters.length)
 				filters[filterIdx++].doFilter(req, rsp, this);
 			else
 				servlet.service(req, rsp);
 		}
 	}
 }