/*
    * 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
    *
    *      https://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;
  
  import java.io.ObjectInputStream;
  import java.io.ObjectOutputStream;
  import java.io.Serializable;
  import java.text.DateFormat;
  import java.text.SimpleDateFormat;
  import java.util.Date;
  import java.util.Locale;
  import java.util.TimeZone;
  
  /**
   * TimeStamp class represents the Network Time Protocol (NTP) timestamp as defined in RFC-1305 and SNTP (RFC-2030). It is represented as a 64-bit unsigned
   * fixed-point number in seconds relative to 0-hour on 1-January-1900. The 32-bit low-order bits are the fractional seconds whose precision is about 200
   * picoseconds. Assumes overflow date when date passes MAX_LONG and reverts back to 0 is 2036 and not 1900. Test for most significant bit: if MSB=0 then 2036
   * basis is used otherwise 1900 if MSB=1.
   * <p>
   * Methods exist to convert NTP timestamps to and from the equivalent Java date representation, which is the number of milliseconds since the standard base time
   * known as "the epoch", namely January 1, 1970, 00:00:00 GMT.
   * </p>
   *
   * @see java.util.Date
   */
  public class TimeStamp implements Serializable, Comparable<TimeStamp> {
      private static final long serialVersionUID = 8139806907588338737L;
  
      /**
       * Baseline NTP time if bit-0=0 is 7-Feb-2036 @ 06:28:16 UTC
       */
      protected static final long msb0baseTime = 2085978496000L;
  
      /**
       * Baseline NTP time if bit-0=1 is 1-Jan-1900 @ 01:00:00 UTC
       */
      protected static final long msb1baseTime = -2208988800000L;
  
      /**
       * Default NTP date string format. E.g. Fri, Sep 12 2003 21:06:23.860. See {@code java.text.SimpleDateFormat} for code descriptions.
       */
      public static final String NTP_DATE_FORMAT = "EEE, MMM dd yyyy HH:mm:ss.SSS";
  
      /**
       * Left-pad 8-character hexadecimal string with 0's
       *
       * @param buf   StringBuilder which is appended with leading 0's.
       * @param l     a long.
       */
      private static void appendHexString(final StringBuilder buf, final long l) {
          final String s = Long.toHexString(l);
          for (int i = s.length(); i < 8; i++) {
              buf.append('0');
          }
          buf.append(s);
      }
  
      /**
       * Convert NTP timestamp hexstring (e.g. "c1a089bd.fc904f6d") to the NTP 64-bit unsigned fixed-point number.
       *
       * @param hexString the string to convert
       * @return NTP 64-bit timestamp value.
       * @throws NumberFormatException - if the string does not contain a parsable timestamp.
       */
      protected static long decodeNtpHexString(final String hexString) throws NumberFormatException {
          if (hexString == null) {
              throw new NumberFormatException("null");
          }
          final int ind = hexString.indexOf('.');
          if (ind == -1) {
              if (hexString.isEmpty()) {
                  return 0;
              }
              return Long.parseLong(hexString, 16) << 32; // no decimal
          }
  
          return Long.parseLong(hexString.substring(0, ind), 16) << 32 | Long.parseLong(hexString.substring(ind + 1), 16);
      }
  
      /**
       * Gets an NTP timestamp object and initializes it so that it represents the time at which it was allocated, measured to the nearest millisecond.
       *
       * @return NTP timestamp object set to the current time.
       * @see System#currentTimeMillis()
      */
     public static TimeStamp getCurrentTime() {
         return getNtpTime(System.currentTimeMillis());
     }
 
     // initialization of static time bases
     /*
      * static { TimeZone utcZone = TimeZone.getTimeZone("UTC"); Calendar calendar = Calendar.getInstance(utcZone); calendar.set(1900, Calendar.JANUARY, 1, 0, 0,
      * 0); calendar.set(Calendar.MILLISECOND, 0); msb1baseTime = calendar.getTime().getTime(); calendar.set(2036, Calendar.FEBRUARY, 7, 6, 28, 16);
      * calendar.set(Calendar.MILLISECOND, 0); msb0baseTime = calendar.getTime().getTime(); }
      */
 
     /**
      * Gets an NTP timestamp object from a Java time. Note that Java time (milliseconds) by definition has less precision than NTP time
      * (picoseconds) so converting Ntptime to Javatime and back to Ntptime loses precision. For example, Tue, Dec 17 2002 09:07:24.810 is represented by a
      * single Java-based time value of f22cd1fc8a, but its NTP equivalent are all values from c1a9ae1c.cf5c28f5 to c1a9ae1c.cf9db22c.
      *
      * @param dateMillis the milliseconds since January 1, 1970, 00:00:00 GMT.
      * @return NTP timestamp object at the specified date.
      */
     public static TimeStamp getNtpTime(final long dateMillis) {
         return new TimeStamp(toNtpTime(dateMillis));
     }
 
     /**
      * Gets a Java standard time from a 64-bit NTP timestamp.
      *
      * Note that java time (milliseconds) by definition has less precision than NTP time (picoseconds) so converting NTP timestamp to Java time and back to NTP
      * timestamp loses precision. For example, Tue, Dec 17 2002 09:07:24.810 EST is represented by a single Java-based time value of f22cd1fc8a, but its NTP
      * equivalent are all values ranging from c1a9ae1c.cf5c28f5 to c1a9ae1c.cf9db22c.
      *
      * @param ntpTimeValue the input time
      * @return the number of milliseconds since January 1, 1970, 00:00:00 GMT represented by this NTP timestamp value.
      */
     public static long getTime(final long ntpTimeValue) {
         final long seconds = ntpTimeValue >>> 32 & 0xffffffffL; // high-order 32-bits
         long fraction = ntpTimeValue & 0xffffffffL; // low-order 32-bits
 
         // Use round-off on fractional part to preserve going to lower precision
         fraction = Math.round(1000D * fraction / 0x100000000L);
 
         /*
          * If the most significant bit (MSB) on the seconds field is set we use a different time base. The following text is a quote from RFC-2030 (SNTP v4):
          *
          * If bit 0 is set, the UTC time is in the range 1968-2036 and UTC time is reckoned from 0h 0m 0s UTC on 1 January 1900. If bit 0 is not set, the time
          * is in the range 2036-2104 and UTC time is reckoned from 6h 28m 16s UTC on 7 February 2036.
          */
         final long msb = seconds & 0x80000000L;
         if (msb == 0) {
             // use base: 7-Feb-2036 @ 06:28:16 UTC
             return msb0baseTime + seconds * 1000 + fraction;
         }
         // use base: 1-Jan-1900 @ 01:00:00 UTC
         return msb1baseTime + seconds * 1000 + fraction;
     }
 
     /**
      * Parses the string argument as a NTP hexidecimal timestamp representation string (e.g. "c1a089bd.fc904f6d").
      *
      * @param s   hexstring.
      * @return the Timestamp represented by the argument in hexidecimal.
      * @throws NumberFormatException - if the string does not contain a parsable timestamp.
      */
     public static TimeStamp parseNtpString(final String s) throws NumberFormatException {
         return new TimeStamp(decodeNtpHexString(s));
     }
 
     /**
      * Converts Java time to 64-bit NTP time representation.
      *
      * @param millis Java time
      * @return NTP timestamp representation of Java time value.
      */
     protected static long toNtpTime(final long millis) {
         final boolean useBase1 = millis < msb0baseTime; // time < Feb-2036
         final long baseTimeMillis;
         if (useBase1) {
             baseTimeMillis = millis - msb1baseTime; // dates <= Feb-2036
         } else {
             // if base0 needed for dates >= Feb-2036
             baseTimeMillis = millis - msb0baseTime;
         }
 
         long seconds = baseTimeMillis / 1000;
         final long fraction = baseTimeMillis % 1000 * 0x100000000L / 1000;
 
         if (useBase1) {
             seconds |= 0x80000000L; // set high-order bit if msb1baseTime 1900 used
         }
 
         return seconds << 32 | fraction;
     }
 
     /**
      * Converts 64-bit NTP timestamp value to a {@code String}. The NTP timestamp value is represented as hexadecimal string with seconds separated by
      * fractional seconds by a decimal point; e.g. c1a089bd.fc904f6d == Tue, Dec 10 2002 10:41:49.986
      *
      * @param ntpTime the 64 bit timestamp
      * @return NTP timestamp 64-bit long value as hexadecimal string with seconds separated by fractional seconds.
      */
     public static String toString(final long ntpTime) {
         final StringBuilder buf = new StringBuilder();
         // high-order second bits (32..63) as hexstring
         appendHexString(buf, ntpTime >>> 32 & 0xffffffffL);
 
         // low-order fractional seconds bits (0..31) as hexstring
         buf.append('.');
         appendHexString(buf, ntpTime & 0xffffffffL);
 
         return buf.toString();
     }
 
     /**
      * NTP timestamp value: 64-bit unsigned fixed-point number as defined in RFC-1305 with high-order 32 bits the seconds field and the low-order 32-bits the
      * fractional field.
      */
     private final long ntpTime;
 
     /**
      * Formats dates.
      */
     private DateFormat simpleFormatter;
 
     /**
      * Formats UTC strings.
      */
     private DateFormat utcFormatter;
 
     /**
      * Constructs a newly allocated NTP timestamp object that represents the Java Date argument.
      *
      * @param d   the Date to be represented by the Timestamp object.
      */
     public TimeStamp(final Date d) {
         ntpTime = d == null ? 0 : toNtpTime(d.getTime());
     }
 
     /**
      * Constructs a newly allocated NTP timestamp object that represents the native 64-bit long argument.
      *
      * @param ntpTime the timestamp
      */
     public TimeStamp(final long ntpTime) {
         this.ntpTime = ntpTime;
     }
 
     /**
      * Constructs a newly allocated NTP timestamp object that represents the value represented by the string in hexdecimal form (e.g. "c1a089bd.fc904f6d").
      *
      * @param hexStamp the hexadecimal timestamp
      * @throws NumberFormatException - if the string does not contain a parsable timestamp.
      */
     public TimeStamp(final String hexStamp) throws NumberFormatException {
         ntpTime = decodeNtpHexString(hexStamp);
     }
 
     /**
      * Compares two Timestamps numerically.
      *
      * @param anotherTimeStamp   the {@code TimeStamp} to be compared.
      * @return the value {@code 0} if the argument TimeStamp is equal to this TimeStamp; a value less than {@code 0} if this TimeStamp is numerically
      *         less than the TimeStamp argument; and a value greater than {@code 0} if this TimeStamp is numerically greater than the TimeStamp argument
      *         (signed comparison).
      */
     @Override
     public int compareTo(final TimeStamp anotherTimeStamp) {
         final long thisVal = ntpTime;
         final long anotherVal = anotherTimeStamp.ntpTime;
         return Long.compare(thisVal, anotherVal);
     }
 
     /**
      * Compares this object against the specified object. The result is {@code true} if and only if the argument is not {@code null} and is a
      * {@code Long} object that contains the same {@code long} value as this object.
      *
      * @param obj the object to compare with.
      * @return {@code true} if the objects are the same; {@code false} otherwise.
      */
     @Override
     public boolean equals(final Object obj) {
         if (obj instanceof TimeStamp) {
             return ntpTime == ((TimeStamp) obj).ntpValue();
         }
         return false;
     }
 
     /**
      * Gets a Date for an NTP timestamp.
      *
      * @return NTP Timestamp in Java Date
      */
     public Date getDate() {
         return new Date(getTime(ntpTime));
     }
 
     /**
      * Gets the low-order 32-bits representing the fractional seconds.
      *
      * @return fractional seconds represented by this NTP timestamp.
      */
     public long getFraction() {
         return ntpTime & 0xffffffffL;
     }
 
     /**
      * Gets the high-order 32-bits representing the seconds of this NTP timestamp.
      *
      * @return seconds represented by this NTP timestamp.
      */
     public long getSeconds() {
         return ntpTime >>> 32 & 0xffffffffL;
     }
 
     /**
      * Gets a Java standard time in milliseconds from the NTP timestamp.
      *
      * @return the number of milliseconds since January 1, 1970, 00:00:00 GMT represented by this NTP timestamp value.
      */
     public long getTime() {
         return getTime(ntpTime);
     }
 
     /**
      * Computes a hash code for this Timestamp. The result is the exclusive OR of the two halves of the primitive {@code long} value represented by this
      * {@code TimeStamp} object. That is, the hash code is the value of the expression: <blockquote>
      *
      * <pre>
      * {@code
      * (int) (this.ntpValue() ^ (this.ntpValue() >>> 32))
      * }
      * </pre>
      *
      * </blockquote>
      *
      * @return a hash code value for this object.
      */
     @Override
     public int hashCode() {
         return (int) (ntpTime ^ ntpTime >>> 32);
     }
 
     /**
      * Returns the value of this Timestamp as a long value.
      *
      * @return the 64-bit long value represented by this object.
      */
     public long ntpValue() {
         return ntpTime;
     }
 
     /**
      * Throws UnsupportedOperationException.
      *
      * @param ignored Ignored.
      */
     private void readObject(final ObjectInputStream ignored) {
         throw new UnsupportedOperationException("Serialization is not supported");
     }
 
     /**
      * Converts this {@code TimeStamp} object to a {@code String} of the form: <blockquote>
      *
      * <pre>
      * EEE, MMM dd yyyy HH:mm:ss.SSS
      * </pre>
      *
      * </blockquote> See java.text.SimpleDataFormat for code descriptions.
      *
      * @return a string representation of this date.
      */
     public String toDateString() {
         if (simpleFormatter == null) {
             simpleFormatter = new SimpleDateFormat(NTP_DATE_FORMAT, Locale.US);
             simpleFormatter.setTimeZone(TimeZone.getDefault());
         }
         final Date ntpDate = getDate();
         return simpleFormatter.format(ntpDate);
     }
 
     /**
      * Converts this {@code TimeStamp} object to a {@code String}. The NTP timestamp 64-bit long value is represented as hexadecimal string with
      * seconds separated by fractional seconds by a decimal point; e.g. c1a089bd.fc904f6d == Tue, Dec 10 2002 10:41:49.986
      *
      * @return NTP timestamp 64-bit long value as hexadecimal string with seconds separated by fractional seconds.
      */
     @Override
     public String toString() {
         return toString(ntpTime);
     }
 
     /*
      * Serialization is unnecessary for this class. Reject attempts to do so until such time as the Serializable attribute can be dropped.
      */
 
     /**
      * Converts this {@code TimeStamp} object to a {@code String} of the form: <blockquote>
      *
      * <pre>
      * EEE, MMM dd yyyy HH:mm:ss.SSS UTC
      * </pre>
      *
      * </blockquote> See java.text.SimpleDataFormat for code descriptions.
      *
      * @return a string representation of this date in UTC.
      */
     public String toUTCString() {
         if (utcFormatter == null) {
             utcFormatter = new SimpleDateFormat(NTP_DATE_FORMAT + " 'UTC'", Locale.US);
             utcFormatter.setTimeZone(TimeZone.getTimeZone("UTC"));
         }
         final Date ntpDate = getDate();
         return utcFormatter.format(ntpDate);
     }
 
     /**
      * Always throws {@link UnsupportedOperationException}.
      *
      * @param ignored ignored.
      * @throws UnsupportedOperationException Always thrown.
      */
     private void writeObject(final ObjectOutputStream ignored) {
         throw new UnsupportedOperationException("Serialization is not supported");
     }
 
 }