根据时间表查找下一个循环日期

假设我需要找出下一个计划日期是什么时候，当我知道计划是基于8/1/2014的开始日期，它应该每7天运行一次，当前日期是8/10/2014。我应该得到2014年8月14日的日期。我最终想让这段代码每X小时、每X天、每X周工作一次，但现在我只是用几天来测试。我有下面的代码，我用来计算下一个运行时间，但我让它为一个日期工作，然后它失败了另一个。仅供参考，我使用选项来指定当前日期用于测试目的。我做错了什么?

public class ScheduleComputer
{
    public DateTime GetNextRunTime(ScheduleRequest request)
    {
        var daysSinceBase = ((int)((request.CurrentDate - request.BaseDate).TotalDays)) + 1;
        var partialIntervalsSinceBaseDate = daysSinceBase % request.Interval;
        var fullIntervalsSinceBaseDate = daysSinceBase / request.Interval;
        var daysToNextRun = 0;
        if (partialIntervalsSinceBaseDate > 0)
        {
            daysToNextRun = (request.Interval - partialIntervalsSinceBaseDate) + 1;
        }
        var nextRunDate = request.BaseDate.AddDays((fullIntervalsSinceBaseDate * request.Interval) + daysToNextRun - 1);
        return nextRunDate;
    }
}
public class ScheduleRequest
{
    private readonly DateTime _currentDate;
    public ScheduleRequest()
    {
        _currentDate = DateTime.Now;
    }
    public ScheduleRequest(DateTime currentDate)
    {
        _currentDate = currentDate;
    }
    public DateTime CurrentDate
    {
        get { return _currentDate; }
    }
    public DateTime BaseDate { get; set; }
    public Schedule Schedule { get; set; }
    public int Interval { get; set; }
}
public enum Schedule
{
    Hourly,
    Daily,
    Weekly
}

这里是我的单元测试

[TestFixture]
public class ScheduleComputerTests
{
    private ScheduleComputer _scheduleComputer;
    [SetUp]
    public void SetUp()
    {
        _scheduleComputer = new ScheduleComputer();
    }
    [Test]
    public void ThisTestPassesAndItShould()
    {
        var scheduleRequest = new ScheduleRequest(currentDate: DateTime.Parse("8/14/2014"))
        {
            BaseDate = DateTime.Parse("8/1/2014"),
            Schedule = Schedule.Daily,
            Interval = 7
        };
        var result = _scheduleComputer.GetNextRunTime(scheduleRequest);
        Assert.AreEqual(DateTime.Parse("8/14/2014"), result);
    }
    [Test]
    public void ThisTestFailsAndItShouldNot()
    {
        var scheduleRequest = new ScheduleRequest(currentDate: DateTime.Parse("8/2/2014"))
        {
            BaseDate = DateTime.Parse("8/1/2014"),
            Schedule = Schedule.Daily,
            Interval = 7
        };
        var result = _scheduleComputer.GetNextRunTime(scheduleRequest);
        Assert.AreEqual(DateTime.Parse("8/7/2014"), result);
    }

仅供参考，我在这里看到了这篇文章，但我似乎无法根据我的需要量身定制。

——UPDATE 1——

这是我更新的代码。我知道我用变量使它冗长，这样我可以更好地理解逻辑(希望这不会对性能产生太大影响)。我还添加了处理不同时间段(小时、天、周)的逻辑，并添加了扩展方法，使代码更简洁。然而，这段代码似乎在几小时和几天内完美地工作，但在几周内就失败了。有些地方我没有正确地乘或除7。

public class ScheduleComputer
{
    public DateTime GetNextRunTime(ScheduleRequest request)
    {
        var timeBetwenCurrentAndBase = request.CurrentDate - request.BaseDate;
        var totalPeriodsBetwenCurrentAndBase = timeBetwenCurrentAndBase.TotalPeriods(request.Schedule);
        var fractionalIntervals = totalPeriodsBetwenCurrentAndBase % request.Interval;
        var partialIntervalsLeft = request.Interval - fractionalIntervals;
        if (request.Schedule != Schedule.Hourly) partialIntervalsLeft = partialIntervalsLeft - 1;
        var nextRunTime = request.CurrentDate.AddPeriods(partialIntervalsLeft, request.Schedule);
        return nextRunTime;
    }
}
public static class ScheduleComputerExtensions
{
    public static double TotalPeriods(this TimeSpan timeBetwenCurrentAndBase, Schedule schedule)
    {
        switch (schedule)
        {
            case Schedule.Hourly: return timeBetwenCurrentAndBase.TotalHours;
            case Schedule.Daily: return timeBetwenCurrentAndBase.TotalDays;
            case Schedule.Weekly: return timeBetwenCurrentAndBase.TotalDays * 7;
            default: throw new ApplicationException("Invalid Schedule Provided");
        }
    }
    public static DateTime AddPeriods(this DateTime dateTime, double partialIntervalsLeft, Schedule schedule)
    {
        switch (schedule)
        {
            case Schedule.Hourly: return dateTime.AddHours(partialIntervalsLeft);
            case Schedule.Daily: return dateTime.AddDays(partialIntervalsLeft);
            case Schedule.Weekly: return dateTime.AddDays(partialIntervalsLeft * 7);
            default: throw new ApplicationException("Invalid Schedule Provided");
        }
    }
}