/*
    * 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.lang3.time;
  
  import java.time.LocalDateTime;
  import java.time.OffsetDateTime;
  import java.time.ZoneId;
  import java.time.ZonedDateTime;
  import java.util.Calendar;
  import java.util.Locale;
  import java.util.Locale.Category;
  import java.util.Map;
  import java.util.Objects;
  
  /**
   * Helps use {@link Calendar}s.
   *
   * @since 3.10
   */
  public class CalendarUtils {
  
      /**
       * The singleton instance for {@link Calendar#getInstance()}. The instance is created when the class is initialized and is based on the current time in the
       * default time zone with the default {@link Category#FORMAT} locale.
       *
       * @see CalendarUtils#getInstance()
       */
      public static final CalendarUtils INSTANCE = getInstance();
  
      /**
       * Creates a new instance based on the current time in the default time zone with the default {@link Category#FORMAT} locale.
       *
       * @return a new instance.
       * @since 3.14.0
       */
      public static CalendarUtils getInstance() {
          return new CalendarUtils(Calendar.getInstance());
      }
  
      /**
       * Gets a CalendarUtils using the default time zone and specified locale. The {@code CalendarUtils} returned is based on the current time in the
       * default time zone with the given locale.
       *
       * @param locale the locale for the week data
       * @return a Calendar.
       */
      static CalendarUtils getInstance(final Locale locale) {
          return new CalendarUtils(Calendar.getInstance(locale), locale);
      }
  
      /**
       * Converts a Calendar to a LocalDateTime.
       *
       * @param calendar the Calendar to convert.
       * @return a LocalDateTime.
       * @since 3.17.0
       */
      public static LocalDateTime toLocalDateTime(final Calendar calendar) {
          return LocalDateTime.ofInstant(calendar.toInstant(), toZoneId(calendar));
      }
  
      /**
       * Converts a Calendar to a OffsetDateTime.
       *
       * @param calendar the Calendar to convert.
       * @return a OffsetDateTime.
       * @since 3.17.0
       */
      public static OffsetDateTime toOffsetDateTime(final Calendar calendar) {
          return OffsetDateTime.ofInstant(calendar.toInstant(), toZoneId(calendar));
      }
  
      /**
       * Converts a Calendar to a ZonedDateTime.
       *
       * @param calendar the Calendar to convert.
       * @return a ZonedDateTime.
       * @since 3.17.0
       */
      public static ZonedDateTime toZonedDateTime(final Calendar calendar) {
          return ZonedDateTime.ofInstant(calendar.toInstant(), toZoneId(calendar));
      }
  
      private static ZoneId toZoneId(final Calendar calendar) {
         return calendar.getTimeZone().toZoneId();
     }
 
     private final Calendar calendar;
 
     private final Locale locale;
 
     /**
      * Creates an instance for the given Calendar.
      *
      * @param calendar A Calendar.
      */
     public CalendarUtils(final Calendar calendar) {
         this(calendar, Locale.getDefault());
     }
     /**
      * Creates an instance for the given Calendar.
      *
      * @param calendar A Calendar.
      * @param locale A Locale.
      */
     CalendarUtils(final Calendar calendar, final Locale locale) {
         this.calendar = Objects.requireNonNull(calendar, "calendar");
         this.locale = Objects.requireNonNull(locale, "locale");
     }
 
     /**
      * Gets the current day of month.
      *
      * @return the current day of month.
      */
     public int getDayOfMonth() {
         return calendar.get(Calendar.DAY_OF_MONTH);
     }
 
     /**
      * Gets the current day of year.
      *
      * @return the current day of year.
      * @since 3.13.0
      */
     public int getDayOfYear() {
         return calendar.get(Calendar.DAY_OF_YEAR);
     }
 
     /**
      * Gets the current month.
      *
      * @return the current month.
      */
     public int getMonth() {
         return calendar.get(Calendar.MONTH);
     }
 
     /**
      * Gets month names in the requested style.
      * @param style Must be a valid {@link Calendar#getDisplayNames(int, int, Locale)} month style.
      * @return Styled names of months
      */
     String[] getMonthDisplayNames(final int style) {
         // Unfortunately standalone month names are not available in DateFormatSymbols,
         // so we have to extract them.
         final Map<String, Integer> displayNames = calendar.getDisplayNames(Calendar.MONTH, style, locale);
         if (displayNames == null) {
             return null;
         }
         final String[] monthNames = new String[displayNames.size()];
         displayNames.forEach((k, v) -> monthNames[v] = k);
         return monthNames;
     }
 
     /**
      * Gets full standalone month names as used in "LLLL" date formatting.
      * @return Long names of months
      */
     String[] getStandaloneLongMonthNames() {
         return getMonthDisplayNames(Calendar.LONG_STANDALONE);
     }
 
     /**
      * Gets short standalone month names as used in "LLLL" date formatting.
      * @return Short names of months
      */
     String[] getStandaloneShortMonthNames() {
         return getMonthDisplayNames(Calendar.SHORT_STANDALONE);
     }
 
     /**
      * Gets the current year.
      *
      * @return the current year.
      */
     public int getYear() {
         return calendar.get(Calendar.YEAR);
     }
 
     /**
      * Converts this instance to a {@link LocalDateTime}.
      *
      * @return a LocalDateTime.
      * @since 3.17.0
      */
     public LocalDateTime toLocalDateTime() {
         return toLocalDateTime(calendar);
     }
 
     /**
      * Converts this instance to a {@link OffsetDateTime}.
      *
      * @return a OffsetDateTime.
      * @since 3.17.0
      */
     public OffsetDateTime toOffsetDateTime() {
         return toOffsetDateTime(calendar);
     }
 
     /**
      * Converts this instance to a {@link ZonedDateTime}.
      *
      * @return a ZonedDateTime.
      * @since 3.17.0
      */
     public ZonedDateTime toZonedDateTime() {
         return toZonedDateTime(calendar);
     }
 
 }