查找两个时区之间的所有时区偏移周期

我的代码将为两个日期之间的所有周期提供目标时区和源时区之间以秒为单位的偏移量。

下面的代码将这样做:

// example start and end date
DateTime startDate = DateTime.SpecifyKind(DateTime.Now.Date, DateTimeKind.Unspecified);
DateTime endDate = startDate.AddYears(10);
// the timezones to use
var sourceZone = TimeZoneInfo.FindSystemTimeZoneById("GMT Standard Time");
var destinationZone = TimeZoneInfo.FindSystemTimeZoneById("Mountain Standard Time");
// the periods and timezone offsets
var results = new List<Tuple<DateTime, DateTime, double>>();
// loop variables
DateTime currentDate = startDate;
DateTime periodStartDate = currentDate;
// the current period offset (in seconds)
double? currentOffset = null;
while (currentDate < endDate)
{
    DateTime destTime;
    // if the current time is invalid for the source timezone
    // then advance time until it is not invalid
    while (sourceZone.IsInvalidTime(currentDate))
        currentDate = currentDate.AddMinutes(30d);
    destTime = TimeZoneInfo.ConvertTime(currentDate, sourceZone, destinationZone);
    // calculate the offset for this iteration
    double iterationOffset = destTime.Subtract(currentDate).TotalSeconds;
    if (currentOffset == null)
        // the current offset is null so use the iteration offset
        currentOffset = iterationOffset;
    else if (iterationOffset != currentOffset.Value)
    {
        // the current offset doesn't equal the iteration offset
        // that means that a period has been identified
        // add the period to the list
        results.Add(Tuple.Create(periodStartDate, currentDate, currentOffset.Value));
        // the start of the period is the new current date
        periodStartDate = currentDate;
        // the current offset becomes the iteration offset
        currentOffset = iterationOffset;
    }
    // increment the day by 30 minutes
    currentDate = currentDate.AddMinutes(30d);
}
foreach (var item in results)
    Console.WriteLine("{0}'t{1}'t{2}", item.Item1, item.Item2, item.Item3);

结果:

╔═══════════════════════╦═══════════════════════╦════════╗
║      PeriodStart      ║       PeriodEnd       ║ Offset ║
╠═══════════════════════╬═══════════════════════╬════════╣
║ 7/13/2015 12:00:00 AM ║ 10/25/2015 1:00:00 AM ║ -25200 ║
║ 10/25/2015 1:00:00 AM ║ 11/1/2015 8:00:00 AM  ║ -21600 ║
║ 11/1/2015 8:00:00 AM  ║ 3/13/2016 9:00:00 AM  ║ -25200 ║
║ 3/13/2016 9:00:00 AM  ║ 3/27/2016 2:00:00 AM  ║ -21600 ║
║ 3/27/2016 2:00:00 AM  ║ 10/30/2016 1:00:00 AM ║ -25200 ║
║ 10/30/2016 1:00:00 AM ║ 11/6/2016 8:00:00 AM  ║ -21600 ║
║ 11/6/2016 8:00:00 AM  ║ 3/12/2017 9:00:00 AM  ║ -25200 ║
║ 3/12/2017 9:00:00 AM  ║ 3/26/2017 2:00:00 AM  ║ -21600 ║
║ 3/26/2017 2:00:00 AM  ║ 10/29/2017 1:00:00 AM ║ -25200 ║
║ 10/29/2017 1:00:00 AM ║ 11/5/2017 8:00:00 AM  ║ -21600 ║
║ 11/5/2017 8:00:00 AM  ║ 3/11/2018 9:00:00 AM  ║ -25200 ║
║          ...          ║          ...          ║   ...  ║
╚═══════════════════════╩═══════════════════════╩════════╝

现在，虽然这似乎有效，但我知道这不是最有效的方法。我基本上坚持将其转换为不需要使用硬编码的时间增量来查找偏移量发生变化的所有周期的方法。

using System;
using System.Linq;
using NodaTime;
...
// Get some time zones.  You can use Tzdb or Bcl zones here.
DateTimeZone sourceZone = DateTimeZoneProviders.Bcl["GMT Standard Time"]; // London
DateTimeZone destinationZone = DateTimeZoneProviders.Bcl["Mountain Standard Time"]; // Denver
// Determine the period of time we're interested in evaluating.
// I'm taking today in the source time zone, up to 10 years in the future.
Instant now = SystemClock.Instance.Now;
Instant start = sourceZone.AtStartOfDay(now.InZone(sourceZone).Date).ToInstant();
Instant end = start.InZone(sourceZone).LocalDateTime.PlusYears(10).InZoneLeniently(sourceZone).ToInstant();
// Get the intervals for our each of the zones over these periods
var sourceIntervals = sourceZone.GetZoneIntervals(start, end);
var destinationIntervals = destinationZone.GetZoneIntervals(start, end);
// Find all of the instants we care about, including the start and end points,
// and all transitions from either zone in between
var instants = sourceIntervals.Union(destinationIntervals)
    .SelectMany(x => new[] {x.Start, x.End})
    .Union(new[] {start, end})
    .OrderBy(x => x).Distinct()
    .Where(x => x >= start && x < end)
    .ToArray();
// Loop through the instants
for (int i = 0; i < instants.Length -1; i++)
{
    // Get this instant and the next one
    Instant instant1 = instants[i];
    Instant instant2 = instants[i + 1];
    // convert each instant to the source zone
    ZonedDateTime zdt1 = instant1.InZone(sourceZone);
    ZonedDateTime zdt2 = instant2.InZone(sourceZone);
    // Get the offsets for instant1 in each zone 
    Offset sourceOffset = zdt1.Offset;
    Offset destOffset = destinationZone.GetUtcOffset(instant1);
    // Calc the difference between the offsets
    int deltaSeconds = (destOffset.Milliseconds - sourceOffset.Milliseconds)/1000;
    // Convert to the same types you had in your example (optional)
    DateTime dt1 = zdt1.ToDateTimeUnspecified();
    DateTime dt2 = zdt2.ToDateTimeUnspecified();
    // emit output
    Console.WriteLine("{0}'t{1}'t{2}", dt1, dt2, deltaSeconds);
}