/*
    * 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.logging.log4j.core.pattern;
  
  import java.text.DateFormat;
  import java.text.FieldPosition;
  import java.text.NumberFormat;
  import java.text.ParsePosition;
  import java.util.Date;
  import java.util.TimeZone;
  
  
  /**
   * CachedDateFormat optimizes the performance of a wrapped
   * DateFormat.  The implementation is not thread-safe.
   * If the millisecond pattern is not recognized,
   * the class will only use the cache if the
   * same value is requested.
   */
  final class CachedDateFormat extends DateFormat {
      /**
       * Constant used to represent that there was no change
       * observed when changing the millisecond count.
       */
      public static final int NO_MILLISECONDS = -2;
  
      /**
       * Constant used to represent that there was an
       * observed change, but was an expected change.
       */
      public static final int UNRECOGNIZED_MILLISECONDS = -1;
  
      /**
       * Supported digit set.  If the wrapped DateFormat uses
       * a different unit set, the millisecond pattern
       * will not be recognized and duplicate requests
       * will use the cache.
       */
      private static final String DIGITS = "0123456789";
  
      /**
       * First magic number used to detect the millisecond position.
       */
      private static final int MAGIC1 = 654;
  
      /**
       * Expected representation of first magic number.
       */
      private static final String MAGICSTRING1 = "654";
  
      /**
       * Second magic number used to detect the millisecond position.
       */
      private static final int MAGIC2 = 987;
  
      /**
       * Expected representation of second magic number.
       */
      private static final String MAGICSTRING2 = "987";
  
      /**
       * Expected representation of 0 milliseconds.
       */
      private static final String ZERO_STRING = "000";
  
      private static final int BUF_SIZE = 50;
  
      private static final int MILLIS_IN_SECONDS = 1000;
  
      private static final int DEFAULT_VALIDITY = 1000;
  
      private static final int THREE_DIGITS = 100;
  
      private static final int TWO_DIGITS = 10;
  
      private static final long SLOTS = 1000L;
  
      /**
       * Wrapped formatter.
       */
      private final DateFormat formatter;
  
      /**
       * Index of initial digit of millisecond pattern or
       * UNRECOGNIZED_MILLISECONDS or NO_MILLISECONDS.
      */
     private int millisecondStart;
 
     /**
      * Integral second preceding the previous convered Date.
      */
     private long slotBegin;
 
     /**
      * Cache of previous conversion.
      */
     private StringBuffer cache = new StringBuffer(BUF_SIZE);
 
     /**
      * Maximum validity period for the cache.
      * Typically 1, use cache for duplicate requests only, or
      * 1000, use cache for requests within the same integral second.
      */
     private final int expiration;
 
     /**
      * Date requested in previous conversion.
      */
     private long previousTime;
 
     /**
      * Scratch date object used to minimize date object creation.
      */
     private final Date tmpDate = new Date(0);
 
     /**
      * Creates a new CachedDateFormat object.
      *
      * @param dateFormat Date format, may not be null.
      * @param expiration maximum cached range in milliseconds.
      *                   If the dateFormat is known to be incompatible with the
      *                   caching algorithm, use a value of 0 to totally disable
      *                   caching or 1 to only use cache for duplicate requests.
      */
     public CachedDateFormat(final DateFormat dateFormat, final int expiration) {
         if (dateFormat == null) {
             throw new IllegalArgumentException("dateFormat cannot be null");
         }
 
         if (expiration < 0) {
             throw new IllegalArgumentException("expiration must be non-negative");
         }
 
         formatter = dateFormat;
         this.expiration = expiration;
         millisecondStart = 0;
 
         //
         //   set the previousTime so the cache will be invalid
         //        for the next request.
         previousTime = Long.MIN_VALUE;
         slotBegin = Long.MIN_VALUE;
     }
 
     /**
      * Finds start of millisecond field in formatted time.
      *
      * @param time      long time, must be integral number of seconds
      * @param formatted String corresponding formatted string
      * @param formatter DateFormat date format
      * @return int position in string of first digit of milliseconds,
      *         -1 indicates no millisecond field, -2 indicates unrecognized
      *         field (likely RelativeTimeDateFormat)
      */
     public static int findMillisecondStart(final long time, final String formatted, final DateFormat formatter) {
         long slotBegin = (time / MILLIS_IN_SECONDS) * MILLIS_IN_SECONDS;
 
         if (slotBegin > time) {
             slotBegin -= MILLIS_IN_SECONDS;
         }
 
         int millis = (int) (time - slotBegin);
 
         int magic = MAGIC1;
         String magicString = MAGICSTRING1;
 
         if (millis == MAGIC1) {
             magic = MAGIC2;
             magicString = MAGICSTRING2;
         }
 
         String plusMagic = formatter.format(new Date(slotBegin + magic));
 
         /**
          *   If the string lengths differ then
          *      we can't use the cache except for duplicate requests.
          */
         if (plusMagic.length() != formatted.length()) {
             return UNRECOGNIZED_MILLISECONDS;
         } else {
             // find first difference between values
             for (int i = 0; i < formatted.length(); i++) {
                 if (formatted.charAt(i) != plusMagic.charAt(i)) {
                     //
                     //   determine the expected digits for the base time
                     StringBuffer formattedMillis = new StringBuffer("ABC");
                     millisecondFormat(millis, formattedMillis, 0);
 
                     String plusZero = formatter.format(new Date(slotBegin));
 
                     //   If the next 3 characters match the magic
                     //      string and the expected string
                     if (
                         (plusZero.length() == formatted.length())
                             && magicString.regionMatches(
                             0, plusMagic, i, magicString.length())
                             && formattedMillis.toString().regionMatches(
                             0, formatted, i, magicString.length())
                             && ZERO_STRING.regionMatches(
                             0, plusZero, i, ZERO_STRING.length())) {
                         return i;
                     } else {
                         return UNRECOGNIZED_MILLISECONDS;
                     }
                 }
             }
         }
 
         return NO_MILLISECONDS;
     }
 
     /**
      * Formats a Date into a date/time string.
      *
      * @param date          the date to format.
      * @param sbuf          the string buffer to write to.
      * @param fieldPosition remains untouched.
      * @return the formatted time string.
      */
     public StringBuffer format(Date date, StringBuffer sbuf, FieldPosition fieldPosition) {
         format(date.getTime(), sbuf);
 
         return sbuf;
     }
 
     /**
      * Formats a millisecond count into a date/time string.
      *
      * @param now Number of milliseconds after midnight 1 Jan 1970 GMT.
      * @param buf the string buffer to write to.
      * @return the formatted time string.
      */
     public StringBuffer format(long now, StringBuffer buf) {
         //
         // If the current requested time is identical to the previously
         //     requested time, then append the cache contents.
         //
         if (now == previousTime) {
             buf.append(cache);
 
             return buf;
         }
 
         //
         //   If millisecond pattern was not unrecognized
         //     (that is if it was found or milliseconds did not appear)
         //
         if (millisecondStart != UNRECOGNIZED_MILLISECONDS &&
             //    Check if the cache is still valid.
             //    If the requested time is within the same integral second
             //       as the last request and a shorter expiration was not requested.
             (now < (slotBegin + expiration)) && (now >= slotBegin) && (now < (slotBegin + SLOTS))) {
             //
             //    if there was a millisecond field then update it
             //
             if (millisecondStart >= 0) {
                 millisecondFormat((int) (now - slotBegin), cache, millisecondStart);
             }
 
             //
             //   update the previously requested time
             //      (the slot begin should be unchanged)
             previousTime = now;
             buf.append(cache);
 
             return buf;
         }
 
         //
         //  could not use previous value.
         //    Call underlying formatter to format date.
         cache.setLength(0);
         tmpDate.setTime(now);
         cache.append(formatter.format(tmpDate));
         buf.append(cache);
         previousTime = now;
         slotBegin = (previousTime / MILLIS_IN_SECONDS) * MILLIS_IN_SECONDS;
 
         if (slotBegin > previousTime) {
             slotBegin -= MILLIS_IN_SECONDS;
         }
 
         //
         //    if the milliseconds field was previous found
         //       then reevaluate in case it moved.
         //
         if (millisecondStart >= 0) {
             millisecondStart =
                 findMillisecondStart(now, cache.toString(), formatter);
         }
 
         return buf;
     }
 
     /**
      * Formats a count of milliseconds (0-999) into a numeric representation.
      *
      * @param millis Millisecond coun between 0 and 999.
      * @param buf    String buffer, may not be null.
      * @param offset Starting position in buffer, the length of the
      *               buffer must be at least offset + 3.
      */
     private static void millisecondFormat(
         final int millis, final StringBuffer buf, final int offset) {
         buf.setCharAt(offset, DIGITS.charAt(millis / THREE_DIGITS));
         buf.setCharAt(offset + 1, DIGITS.charAt((millis / TWO_DIGITS) % TWO_DIGITS));
         buf.setCharAt(offset + 2, DIGITS.charAt(millis % TWO_DIGITS));
     }
 
     /**
      * Set timezone.
      * <p/>
      * Setting the timezone using getCalendar().setTimeZone()
      * will likely cause caching to misbehave.
      *
      * @param timeZone TimeZone new timezone
      */
     public void setTimeZone(final TimeZone timeZone) {
         formatter.setTimeZone(timeZone);
         previousTime = Long.MIN_VALUE;
         slotBegin = Long.MIN_VALUE;
     }
 
     /**
      * This method is delegated to the formatter which most
      * likely returns null.
      *
      * @param s   string representation of date.
      * @param pos field position, unused.
      * @return parsed date, likely null.
      */
     public Date parse(String s, ParsePosition pos) {
         return formatter.parse(s, pos);
     }
 
     /**
      * Gets number formatter.
      *
      * @return NumberFormat number formatter
      */
     public NumberFormat getNumberFormat() {
         return formatter.getNumberFormat();
     }
 
     /**
      * Gets maximum cache validity for the specified SimpleDateTime
      * conversion pattern.
      *
      * @param pattern conversion pattern, may not be null.
      * @return Duration in milliseconds from an integral second
      *         that the cache will return consistent results.
      */
     public static int getMaximumCacheValidity(final String pattern) {
         //
         //   If there are more "S" in the pattern than just one "SSS" then
         //      (for example, "HH:mm:ss,SSS SSS"), then set the expiration to
         //      one millisecond which should only perform duplicate request caching.
         //
         int firstS = pattern.indexOf('S');
 
         if ((firstS >= 0) && (firstS != pattern.lastIndexOf("SSS"))) {
             return 1;
         }
 
         return DEFAULT_VALIDITY;
     }
 }