/*
 * 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.
 On HTTP transports this user agent string is always supplied by the JGit client in the User-Agent HTTP header. 

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/**
 * 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.
Returns:
a string similar to "JGit/4.0"; null if the agent has been cleared and should not be shared with a peer./**
	 * 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.
 The new string should start with "JGit/" (for example "JGit/4.0") to advertise the implementation as JGit based. 
 Spaces and other whitespace should be avoided as these will be automatically converted to ".". 

User agent strings are restricted to printable ASCII.
Params:
agent – 
           new user agent string for this running JGit library. Setting
           to null or empty string will avoid sending any identification
           to the peer./**
	 * 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() {
	}
}