package org.webslinger.util;

 import java.text.SimpleDateFormat;

 import java.util.Calendar;

 import java.util.Locale;

 import java.util.TimeZone;

 // not Thread-safe

 public final class RolloverLogic {

     protected final Calendar cal;

     protected final SimpleDateFormat formatter;

     protected final Period period;

     protected long rolloverTime;

     protected static enum Period {

         YEAR(Calendar.YEAR),

         MONTH(Calendar.MONTH),

         DAY(Calendar.DAY_OF_MONTH),

         AM_PM(Calendar.AM_PM),

         HOUR(Calendar.HOUR_OF_DAY),

         MINUTE(Calendar.MINUTE),

         SECOND(Calendar.SECOND);

         private final int field;

         Period(int field) {

             this.field = field;

         }

         public int field() {

             return field;

         }

     };

     public RolloverLogic(String pattern) {

         this(pattern, System.currentTimeMillis(), Locale.getDefault(), TimeZone.getDefault());

     }

     public RolloverLogic(String pattern, Locale locale, TimeZone timeZone) {

         this(pattern, System.currentTimeMillis(), locale, timeZone);

     }

     public RolloverLogic(String pattern, long currentTime) {

         this(pattern, currentTime, Locale.getDefault(), TimeZone.getDefault());

     }

     public RolloverLogic(String pattern, long currentTime, Locale locale, TimeZone timeZone) {

         cal = Calendar.getInstance(timeZone, locale);

         formatter = new SimpleDateFormat(pattern);

         cal.setTimeInMillis(0);

         Period period = null;

         String s = formatter.format(cal.getTime());

         for (Period periodCheck: Period.values()) {

             cal.add(periodCheck.field(), 1);

             if (!formatter.format(cal.getTime()).equals(s)) period = periodCheck;

             cal.add(periodCheck.field(), -1);

         }

         if (period == null) throw new IllegalArgumentException("Couldn't detect check frequency");

         this.period = period;

         cal.setTimeInMillis(currentTime);

         cal.add(period.field(), 1);

         for (Period p: Period.values()) {

             cal.set(p.field(), 0);

         }

         rolloverTime = cal.getTimeInMillis();

     }

     public final String getPattern() {

         return formatter.toPattern();

     }

     public final long getRolloverTime() {

         return rolloverTime;

     }

     public final boolean checkRollover() {

         long millis = System.currentTimeMillis();

         if (millis < rolloverTime) return false;

         do {

             cal.add(period.field(), 1);

         } while ((rolloverTime = cal.getTimeInMillis()) < millis);

         return true;

     }

     public final String getCurrentFormat() {

         return formatter.format(cal.getTime());

     }

 }