/*
    * Copyright (C) 2015, Google Inc. and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.transport;
  
  import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_AGENT;
  
  import java.util.Set;
  
  import org.eclipse.jgit.util.StringUtils;
  
  /**
   * User agent to be reported by this JGit client and server on the network.
   * <p>
   * On HTTP transports this user agent string is always supplied by the JGit
   * client in the {@code User-Agent} HTTP header.
   * <p>
   * On native transports this user agent string is always sent when JGit is a
   * server. When JGit is a client the user agent string will be supplied to the
   * remote server only if the remote server advertises its own agent identity.
   *
   * @since 4.0
   */
  public class UserAgent {
  	private static volatile String userAgent = computeUserAgent();
  
  	private static String computeUserAgent() {
  		return clean("JGit/" + computeVersion()); //$NON-NLS-1$
  	}
  
  	private static String computeVersion() {
  		Package pkg = UserAgent.class.getPackage();
  		if (pkg != null) {
  			String ver = pkg.getImplementationVersion();
  			if (!StringUtils.isEmptyOrNull(ver)) {
  				return ver;
  			}
  		}
  		return "unknown"; //$NON-NLS-1$
  	}
  
  	static String clean(String s) {
  		s = s.trim();
  		StringBuilder b = new StringBuilder(s.length());
  		for (int i = 0; i < s.length(); i++) {
  			char c = s.charAt(i);
  			if (c <= 32 || c >= 127) {
  				if (b.length() > 0 && b.charAt(b.length() - 1) == '.')
  					continue;
  				c = '.';
  			}
  			b.append(c);
  		}
  		return b.length() > 0 ? b.toString() : null;
  	}
  
  	/**
  	 * Get the user agent string advertised by JGit.
  	 *
  	 * @return a string similar to {@code "JGit/4.0"}; null if the agent has
  	 *         been cleared and should not be shared with a peer.
  	 */
  	public static String get() {
  		return userAgent;
  	}
  
  	/**
  	 * Change the user agent string advertised by JGit.
  	 * <p>
  	 * The new string should start with {@code "JGit/"} (for example
  	 * {@code "JGit/4.0"}) to advertise the implementation as JGit based.
  	 * <p>
  	 * Spaces and other whitespace should be avoided as these will be
  	 * automatically converted to {@code "."}.
  	 * <p>
  	 * User agent strings are restricted to printable ASCII.
  	 *
  	 * @param agent
  	 *            new user agent string for this running JGit library. Setting
  	 *            to null or empty string will avoid sending any identification
  	 *            to the peer.
  	 */
  	public static void set(String agent) {
  		userAgent = StringUtils.isEmptyOrNull(agent) ? null : clean(agent);
  	}
  
  	static String getAgent(Set<String> options, String transportAgent) {
  		if (options == null || options.isEmpty()) {
  			return transportAgent;
  		}
  		for (String o : options) {
  			if (o.startsWith(OPTION_AGENT)
 					&& o.length() > OPTION_AGENT.length()
 					&& o.charAt(OPTION_AGENT.length()) == '=') {
 				return o.substring(OPTION_AGENT.length() + 1);
 			}
 		}
 		return transportAgent;
 	}
 
 	static boolean hasAgent(Set<String> options) {
 		return getAgent(options, null) != null;
 	}
 
 	private UserAgent() {
 	}
 }