/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.commons.net.ntp;

/**
 * Common NtpUtils Helper class.
 *
 */
public final class NtpUtils {

    /**
     * Returns 32-bit integer address to IPv4 address string "%d.%d.%d.%d" format.
     *
     * @param address the 32-bit address
     * @return the raw IP address in a string format.
     */
    public static String getHostAddress(final int address) {
        return ((address >>> 24) & 0xFF) + "." + ((address >>> 16) & 0xFF) + "." + ((address >>> 8) & 0xFF) + "." + ((address >>> 0) & 0xFF);
    }

    /**
     * Return human-readable name of message mode type (RFC 1305).
     *
     * @param mode the mode type
     * @return mode name
     */
    public static String getModeName(final int mode) {
        switch (mode) {
        case NtpV3Packet.MODE_RESERVED:
            return "Reserved";
        case NtpV3Packet.MODE_SYMMETRIC_ACTIVE:
            return "Symmetric Active";
        case NtpV3Packet.MODE_SYMMETRIC_PASSIVE:
            return "Symmetric Passive";
        case NtpV3Packet.MODE_CLIENT:
            return "Client";
        case NtpV3Packet.MODE_SERVER:
            return "Server";
        case NtpV3Packet.MODE_BROADCAST:
            return "Broadcast";
        case NtpV3Packet.MODE_CONTROL_MESSAGE:
            return "Control";
        case NtpV3Packet.MODE_PRIVATE:
            return "Private";
        default:
            return "Unknown";
        }
    }

    /**
     * Returns NTP packet reference identifier as IP address.
     *
     * @param packet NTP packet
     * @return the packet reference id (as IP address) in "%d.%d.%d.%d" format.
     */
    public static String getRefAddress(final NtpV3Packet packet) {
        final int address = (packet == null) ? 0 : packet.getReferenceId();
        return getHostAddress(address);
    }

    /**
     * Get refId as reference clock string (e.g. GPS, WWV, LCL). If string is invalid (non-ASCII character) then returns empty string "". For details refer to
     * the <A HREF="http://www.eecis.udel.edu/~mills/ntp/html/refclock.html#list">Comprehensive List of Clock Drivers</A>.
     *
     * @param message the message to check
     * @return reference clock string if primary NTP server
     */
    public static String getReferenceClock(final NtpV3Packet message) {
        if (message == null) {
            return "";
        }
        final int refId = message.getReferenceId();
        if (refId == 0) {
            return "";
        }
        final StringBuilder buf = new StringBuilder(4);
        // start at highest-order byte (0x4c434c00 -> LCL)
        for (int shiftBits = 24; shiftBits >= 0; shiftBits -= 8) {
            final char c = (char) ((refId >>> shiftBits) & 0xff);
            if (c == 0) { // 0-terminated ASCII string
                break;
            }
            if (!Character.isLetterOrDigit(c)) {
                return "";
            }
            buf.append(c);
        }
        return buf.toString();
    }

}
