Linq lambda表达式-查找一周中距离当前日期最近的一天（现在）

Question

例如，我有星期一、星期四和星期日作为抽签日期。找到离日期时间最近的星期几的方法是什么。现在使用Linq Lambda？我用正常功能完成了这一点，但我想知道如何使用Linq Lambda？

我的方法示例：

    public static DateTime GetSoonestDrawDate(this DateTime from, IEnumerable<LotteryDrawDate> drawDates)
    {

        int hour = 0;
        int minute = 0;

        bool todayDrawOnly = true;

        int difference = 7;
        int tempDifference = 0;

        int todayDay = (int)from.DayOfWeek;
        int drawCutOffDay = 0;

        if (todayDay == 0)
        {
            todayDay = 7;
        }

        var tempCutOffTime = new TimeSpan(23, 59, 59);

        foreach (var drawDate in drawDates)
        {
            // DayId is DayOfWeek
            drawCutOffDay = drawDate.DayId;

            if (drawCutOffDay < todayDay)
            {
                drawCutOffDay += 7;
            }

            tempDifference = drawCutOffDay - todayDay;

            var cutOffTime = new TimeSpan();
            cutOffTime = TimeSpan.Parse(drawDate.CutOffTime);

            if ((difference > tempDifference) || difference == 0)
            {
                // draw date is not today
                if (tempDifference != 0)
                {
                    difference = tempDifference;
                    hour = cutOffTime.Hours;
                    minute = cutOffTime.Minutes;
                    todayDrawOnly = false;
                }
                // same day, cutOffTime still available
                if ((tempDifference == 0 && cutOffTime > from.TimeOfDay))
                {
                    // we use tempCutOffTime to compare newest cutOffTime in case we have more cutOffTimes on the same day
                    // in that case we have to select the soonest cutOffTime of the day
                    if (cutOffTime < tempCutOffTime)
                    {
                        difference = tempDifference;
                        hour = cutOffTime.Hours;
                        minute = cutOffTime.Minutes;
                        todayDrawOnly = true;
                        tempCutOffTime = cutOffTime;
                    }
                }
                // same day selected only, but cutOffTime passed, so we add another week only in case there is only one draw date and draw date is on the same day
                else if (tempDifference == 0 && cutOffTime < from.TimeOfDay && todayDrawOnly == true)
                {
                    if (cutOffTime < tempCutOffTime)
                    {
                        difference = 7;
                        hour = cutOffTime.Hours;
                        minute = cutOffTime.Minutes;
                        todayDrawOnly = true;
                        tempCutOffTime = cutOffTime;
                    }
                }
            }
        }

        from = from.AddDays(difference);

        DateTime soonest = new DateTime(from.Year, from.Month, from.Day, hour, minute, 0);

        return soonest;
    }

Answer 1

如果你想要一个简单的抽签日硬编码列表，你可以这样做：

DateTime GetNextDate(DateTime from)
{
    DayOfWeek target;
    switch (from.DayOfWeek)
    {
        case DayOfWeek.Friday:
        case DayOfWeek.Saturday:
        case DayOfWeek.Sunday:
            target = DayOfWeek.Sunday;
            break;
        case DayOfWeek.Monday:
            target = DayOfWeek.Monday;
            break;
        case DayOfWeek.Tuesday:
        case DayOfWeek.Wednesday:
        case DayOfWeek.Thursday:
            target = DayOfWeek.Thursday;
            break;
        default:
            throw new ArgumentException("from");
    }
    while (from.DayOfWeek != target)
        from = from.AddDays(1);
    return from;
}

Answer 2

找到未来最近一天的简单方法如下：

DayOfWeek[] draw_days = { DayOfWeek.Sunday, DayOfWeek.Monday, DayOfWeek.Thursday };
Console.WriteLine(
  "Nearest Draw Date: {0}",
  draw_days.Min(d => (d <= DateTime.Now.DayOfWeek) ? (d + 7) : d)
);

Answer 3

因为您没有展示lotterydawdate的样子，所以我只使用DayOfWeek准备了一个小样本。你必须把时间延长到你自己的时间。

public static DateTime GetSoonestDrawDate(this DateTime from, IEnumerable<DayOfWeek> drawDates)
{
    var realDrawDates = drawDates.SelectMany(x => new[] { (int)x, (int)x + 7 }).OrderBy(x => x);
    var difference = realDrawDates.SkipWhile(x => x < (int)from.DayOfWeek).First() - (int)from.DayOfWeek;
    return from.AddDays(difference);
}

小测试代码：

var drawDates = new[] { DayOfWeek.Monday, DayOfWeek.Wednesday, DayOfWeek.Saturday };

for (int i = 0; i < 15; i++)
{
    var from = DateTime.Now.AddDays(i);
    Console.WriteLine("{0} - {1}", from.ToShortDateString(), GetSoonestDrawDate(from, drawDates).ToShortDateString());
}

打印（从-下一页）：

11/18/2013 - 11/18/2013
11/19/2013 - 11/20/2013
11/20/2013 - 11/20/2013
11/21/2013 - 11/23/2013
11/22/2013 - 11/23/2013
11/23/2013 - 11/23/2013
11/24/2013 - 11/25/2013
11/25/2013 - 11/25/2013
11/26/2013 - 11/27/2013
11/27/2013 - 11/27/2013
11/28/2013 - 11/30/2013
11/29/2013 - 11/30/2013
11/30/2013 - 11/30/2013
12/1/2013 - 12/2/2013
12/2/2013 - 12/2/2013