context: /* 
   * 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.
   */
  
  using System;
  using Lucene.Net.Search;
  using NumericUtils = Lucene.Net.Util.NumericUtils;
  
  namespace Lucene.Net.Documents
  {
  	
  	/// <summary> Provides support for converting dates to strings and vice-versa.
  	/// The strings are structured so that lexicographic sorting orders 
  	/// them by date, which makes them suitable for use as field values 
  	/// and search terms.
  	/// 
  	/// <p/>This class also helps you to limit the resolution of your dates. Do not
  	/// save dates with a finer resolution than you really need, as then
  	/// RangeQuery and PrefixQuery will require more memory and become slower.
  	/// 
  	/// <p/>Compared to <see cref="DateField" /> the strings generated by the methods
  	/// in this class take slightly more space, unless your selected resolution
  	/// is set to <c>Resolution.DAY</c> or lower.
  	/// 
  	/// <p/>
  	/// Another approach is <see cref="NumericUtils" />, which provides
  	/// a sortable binary representation (prefix encoded) of numeric values, which
  	/// date/time are.
      /// For indexing a <see cref="DateTime" />, convert it to unix timestamp as
  	/// <c>long</c> and
  	/// index this as a numeric value with <see cref="NumericField" />
  	/// and use <see cref="NumericRangeQuery{T}" /> to query it.
  	/// </summary>
  	public class DateTools
  	{
  		
          private static readonly System.String YEAR_FORMAT = "yyyy";
          private static readonly System.String MONTH_FORMAT = "yyyyMM";
          private static readonly System.String DAY_FORMAT = "yyyyMMdd";
          private static readonly System.String HOUR_FORMAT = "yyyyMMddHH";
          private static readonly System.String MINUTE_FORMAT = "yyyyMMddHHmm";
          private static readonly System.String SECOND_FORMAT = "yyyyMMddHHmmss";
          private static readonly System.String MILLISECOND_FORMAT = "yyyyMMddHHmmssfff";
  		
  		//private static readonly System.Globalization.Calendar calInstance = new System.Globalization.GregorianCalendar();
  		
  		// cannot create, the class has static methods only
  		private DateTools()
  		{
  		}
  		
  		/// <summary> Converts a Date to a string suitable for indexing.
  		/// 
  		/// </summary>
  		/// <param name="date">the date to be converted
  		/// </param>
  		/// <param name="resolution">the desired resolution, see
  		/// <see cref="Round(DateTime, DateTools.Resolution)" />
  		/// </param>
  		/// <returns> a string in format <c>yyyyMMddHHmmssSSS</c> or shorter,
  		/// depending on <c>resolution</c>; using GMT as timezone 
  		/// </returns>
  		public static System.String DateToString(System.DateTime date, Resolution resolution)
  		{
  			return TimeToString(date.Ticks / TimeSpan.TicksPerMillisecond, resolution);
  		}
  		
  		/// <summary> Converts a millisecond time to a string suitable for indexing.
  		/// 
  		/// </summary>
  		/// <param name="time">the date expressed as milliseconds since January 1, 1970, 00:00:00 GMT
  		/// </param>
  		/// <param name="resolution">the desired resolution, see
  		/// <see cref="Round(long, DateTools.Resolution)" />
  		/// </param>
  		/// <returns> a string in format <c>yyyyMMddHHmmssSSS</c> or shorter,
  		/// depending on <c>resolution</c>; using GMT as timezone
  		/// </returns>
  		public static System.String TimeToString(long time, Resolution resolution)
  		{
              var date = new System.DateTime(Round(time, resolution));
  			
  			if (resolution == Resolution.YEAR)
  			{
                  return date.ToString(YEAR_FORMAT, System.Globalization.CultureInfo.InvariantCulture);
  			}
  			else if (resolution == Resolution.MONTH)
  			{
                  return date.ToString(MONTH_FORMAT, System.Globalization.CultureInfo.InvariantCulture);
  			}
  			else if (resolution == Resolution.DAY)
  			{
                  return date.ToString(DAY_FORMAT, System.Globalization.CultureInfo.InvariantCulture);
  			}
  			else if (resolution == Resolution.HOUR)
  			{
                  return date.ToString(HOUR_FORMAT, System.Globalization.CultureInfo.InvariantCulture);
  			}
  			else if (resolution == Resolution.MINUTE)
  			{
                  return date.ToString(MINUTE_FORMAT, System.Globalization.CultureInfo.InvariantCulture);
  			}
  			else if (resolution == Resolution.SECOND)
  			{
                  return date.ToString(SECOND_FORMAT, System.Globalization.CultureInfo.InvariantCulture);
  			}
  			else if (resolution == Resolution.MILLISECOND)
  			{
                  return date.ToString(MILLISECOND_FORMAT, System.Globalization.CultureInfo.InvariantCulture);
  			}
  			
  			throw new System.ArgumentException("unknown resolution " + resolution);
  		}
  		
  		/// <summary> Converts a string produced by <c>timeToString</c> or
  		/// <c>DateToString</c> back to a time, represented as the
  		/// number of milliseconds since January 1, 1970, 00:00:00 GMT.
  		/// 
  		/// </summary>
  		/// <param name="dateString">the date string to be converted
  		/// </param>
  		/// <returns> the number of milliseconds since January 1, 1970, 00:00:00 GMT
  		/// </returns>
  		/// <throws>  ParseException if <c>dateString</c> is not in the  </throws>
  		/// <summary>  expected format 
  		/// </summary>
  		public static long StringToTime(System.String dateString)
  		{
  			return StringToDate(dateString).Ticks;
  		}
  		
  		/// <summary> Converts a string produced by <c>timeToString</c> or
  		/// <c>DateToString</c> back to a time, represented as a
  		/// Date object.
  		/// 
  		/// </summary>
  		/// <param name="dateString">the date string to be converted
  		/// </param>
  		/// <returns> the parsed time as a Date object 
  		/// </returns>
  		/// <throws>  ParseException if <c>dateString</c> is not in the  </throws>
  		/// <summary>  expected format 
  		/// </summary>
  		public static System.DateTime StringToDate(System.String dateString)
  		{
              System.DateTime date;
              if (dateString.Length == 4)
              {
                  date = new System.DateTime(Convert.ToInt16(dateString.Substring(0, 4)),
                      1, 1, 0, 0, 0, 0);
              }
              else if (dateString.Length == 6)
              {
                  date = new System.DateTime(Convert.ToInt16(dateString.Substring(0, 4)),
                      Convert.ToInt16(dateString.Substring(4, 2)),
                      1, 0, 0, 0, 0);
              }
              else if (dateString.Length == 8)
              {
                  date = new System.DateTime(Convert.ToInt16(dateString.Substring(0, 4)),
                      Convert.ToInt16(dateString.Substring(4, 2)),
                      Convert.ToInt16(dateString.Substring(6, 2)),
                      0, 0, 0, 0);
              }
              else if (dateString.Length == 10)
              {
                  date = new System.DateTime(Convert.ToInt16(dateString.Substring(0, 4)),
                      Convert.ToInt16(dateString.Substring(4, 2)),
                      Convert.ToInt16(dateString.Substring(6, 2)),
                      Convert.ToInt16(dateString.Substring(8, 2)),
                      0, 0, 0);
              }
              else if (dateString.Length == 12)
              {
                  date = new System.DateTime(Convert.ToInt16(dateString.Substring(0, 4)),
                      Convert.ToInt16(dateString.Substring(4, 2)),
                      Convert.ToInt16(dateString.Substring(6, 2)),
                      Convert.ToInt16(dateString.Substring(8, 2)),
                      Convert.ToInt16(dateString.Substring(10, 2)),
                      0, 0);
              }
              else if (dateString.Length == 14)
              {
                  date = new System.DateTime(Convert.ToInt16(dateString.Substring(0, 4)),
                      Convert.ToInt16(dateString.Substring(4, 2)),
                      Convert.ToInt16(dateString.Substring(6, 2)),
                      Convert.ToInt16(dateString.Substring(8, 2)),
                      Convert.ToInt16(dateString.Substring(10, 2)),
                      Convert.ToInt16(dateString.Substring(12, 2)),
                      0);
              }
              else if (dateString.Length == 17)
              {
                  date = new System.DateTime(Convert.ToInt16(dateString.Substring(0, 4)),
                      Convert.ToInt16(dateString.Substring(4, 2)),
                      Convert.ToInt16(dateString.Substring(6, 2)),
                      Convert.ToInt16(dateString.Substring(8, 2)),
                      Convert.ToInt16(dateString.Substring(10, 2)),
                      Convert.ToInt16(dateString.Substring(12, 2)),
                      Convert.ToInt16(dateString.Substring(14, 3)));
              }
              else
              {
                  throw new System.FormatException("Input is not valid date string: " + dateString);
              }
              return date;
  		}
  
  	    /// <summary> Limit a date's resolution. For example, the date <c>2004-09-21 13:50:11</c>
  	    /// will be changed to <c>2004-09-01 00:00:00</c> when using
  	    /// <c>Resolution.MONTH</c>. 
  	    /// 
  	    /// </summary>
  	    /// <param name="date"></param>
  	    /// <param name="resolution">The desired resolution of the date to be returned
  	    /// </param>
  	    /// <returns> the date with all values more precise than <c>resolution</c>
  	    /// set to 0 or 1
  	    /// </returns>
  	    public static System.DateTime Round(System.DateTime date, Resolution resolution)
  		{
  			return new System.DateTime(Round(date.Ticks / TimeSpan.TicksPerMillisecond, resolution));
  		}
  		
  		/// <summary> Limit a date's resolution. For example, the date <c>1095767411000</c>
  		/// (which represents 2004-09-21 13:50:11) will be changed to 
  		/// <c>1093989600000</c> (2004-09-01 00:00:00) when using
  		/// <c>Resolution.MONTH</c>.
  		/// 
  		/// </summary>
  		/// <param name="time">The time in milliseconds (not ticks).</param>
  		/// <param name="resolution">The desired resolution of the date to be returned
  		/// </param>
  		/// <returns> the date with all values more precise than <c>resolution</c>
  		/// set to 0 or 1, expressed as milliseconds since January 1, 1970, 00:00:00 GMT
  		/// </returns>
  		public static long Round(long time, Resolution resolution)
  		{
              var dt = new System.DateTime(time * TimeSpan.TicksPerMillisecond);
  			
  			if (resolution == Resolution.YEAR)
  			{
                  dt = dt.AddMonths(1 - dt.Month);
                  dt = dt.AddDays(1 - dt.Day);
                  dt = dt.AddHours(0 - dt.Hour);
                  dt = dt.AddMinutes(0 - dt.Minute);
                  dt = dt.AddSeconds(0 - dt.Second);
                  dt = dt.AddMilliseconds(0 - dt.Millisecond);
              }
  			else if (resolution == Resolution.MONTH)
  			{
                  dt = dt.AddDays(1 - dt.Day);
                  dt = dt.AddHours(0 - dt.Hour);
                  dt = dt.AddMinutes(0 - dt.Minute);
  
gt:                 dt = dt.AddSeconds(0 - dt.Second);