/*
 * Copyright (C) 2012, 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.http.server;

import javax.servlet.http.HttpServletRequest;

/**
 * Parses Git client User-Agent strings.
 */
public class ClientVersionUtil {
	/**
	 * An invalid version of Git
	 *
	 * @return maximum version array, indicating an invalid version of Git.
	 */
	public static int[] invalidVersion() {
		return new int[] { Integer.MAX_VALUE };
	}

	/**
	 * Parse a Git client User-Agent header value.
	 *
	 * @param version
	 *            git client version string, of the form "git/1.7.9".
	 * @return components of the version string. {@link #invalidVersion()} if
	 *         the version string cannot be parsed.
	 */
	public static int[] parseVersion(String version) {
		if (version != null && version.startsWith("git/"))
			return splitVersion(version.substring("git/".length()));
		return invalidVersion();
	}

	private static int[] splitVersion(String versionString) {
		char[] str = versionString.toCharArray();
		int[] ver = new int[4];
		int end = 0;
		int acc = 0;
		for (int i = 0; i < str.length; i++) {
			char c = str[i];
			if ('0' <= c && c <= '9') {
				acc *= 10;
				acc += c - '0';
			} else if (c == '.') {
				if (end == ver.length)
					ver = grow(ver);
				ver[end++] = acc;
				acc = 0;
			} else if (c == 'g' && 0 < i && str[i - 1] == '.' && 0 < end) {
				// Non-tagged builds may contain a mangled git describe output.
				// "1.7.6.1.45.gbe0cc". The 45 isn't a valid component. Drop it.
				ver[end - 1] = 0;
				acc = 0;
				break;
			} else if (c == '-' && (i + 2) < str.length
					&& str[i + 1] == 'r' && str[i + 2] == 'c') {
				// Release candidates aren't the same as a final release.
				if (acc > 0)
					acc--;
				break;
			} else
				break;
		}
		if (acc != 0) {
			if (end == ver.length)
				ver = grow(ver);
			ver[end++] = acc;
		} else {
			while (0 < end && ver[end - 1] == 0)
				end--;
		}
		if (end < ver.length) {
			int[] n = new int[end];
			System.arraycopy(ver, 0, n, 0, end);
			ver = n;
		}
		return ver;
	}

	private static int[] grow(int[] tmp) {
		int[] n = new int[tmp.length + 1];
		System.arraycopy(tmp, 0, n, 0, tmp.length);
		return n;
	}

	/**
	 * Compare two version strings for natural ordering.
	 *
	 * @param a
	 *            first parsed version string.
	 * @param b
	 *            second parsed version string.
	 * @return &lt; 0 if a is before b; 0 if a equals b; &gt;0 if a is after b.
	 */
	public static int compare(int[] a, int[] b) {
		for (int i = 0; i < a.length && i < b.length; i++) {
			int cmp = a[i] - b[i];
			if (cmp != 0)
				return cmp;
		}
		return a.length - b.length;
	}

	/**
	 * Convert a parsed version back to a string.
	 *
	 * @param ver
	 *            the parsed version array.
	 * @return a string, e.g. "1.6.6.0".
	 */
	public static String toString(int[] ver) {
		StringBuilder b = new StringBuilder();
		for (int v : ver) {
			if (b.length() > 0)
				b.append('.');
			b.append(v);
		}
		return b.toString();
	}

	/**
	 * Check if a Git client has the known push status bug.
	 * <p>
	 * These buggy clients do not display the status report from a failed push
	 * over HTTP.
	 *
	 * @param version
	 *            parsed version of the Git client software.
	 * @return true if the bug is present.
	 * @deprecated no widely used Git versions need this any more
	 */
	@Deprecated
	public static boolean hasPushStatusBug(int[] version) {
		return false;
	}

	/**
	 * Check if a Git client has the known chunked request body encoding bug.
	 * <p>
	 * Git 1.7.5 contains a unique bug where chunked requests are malformed.
	 * This applies to both fetch and push.
	 *
	 * @param version
	 *            parsed version of the Git client software.
	 * @param request
	 *            incoming HTTP request.
	 * @return true if the client has the chunked encoding bug.
	 * @deprecated no widely used Git versions need this any more
	 */
	@Deprecated
	public static boolean hasChunkedEncodingRequestBug(
			int[] version, HttpServletRequest request) {
		return false;
	}

	private ClientVersionUtil() {
	}
}