C# 根据第几周和季度 获取开始时间和结束时间

/// <summary>
/// 根据第几周 获取开始时间和结束时间
/// </summary>
/// <param name="week">周数</param>
/// <param name="month">月份</param>
/// <returns></returns>
private Tuple<DateTime, DateTime> GetWeeks(int? week, int? month)
{

DateTime dt = DateTime.Parse($"{DateTime.Now.Year}-{month.Value}-{DateTime.Now.Day}");
string[] arrDate0 = new string[6];
string[] arrDate1 = new string[6];
//年
int year = dt.Year;
//月
//当前月第一天
DateTime weekStart = new DateTime(year, month.Value, 1);
//该月的最后一天
DateTime monEnd = weekStart.AddMonths(1).AddDays(-1);
int i = 1;
//当前月第一天是星期几
int dayOfWeek = Convert.ToInt32(weekStart.DayOfWeek.ToString("d"));
//该月第一周结束日期
DateTime weekEnd = dayOfWeek == 0 ? weekStart : weekStart.AddDays(7 - dayOfWeek);
string content = "";
// content += "第" + i + "周起始日期： " + weekStart.ToShortDateString() + "   结束日期： " + weekEnd.ToShortDateString() + "\n";
arrDate0[0] = weekStart.ToString("yyyy-MM-dd 00:00:00");
arrDate1[0] = weekEnd.ToString("yyyy-MM-dd 23:59:59");

//当日期小于或等于该月的最后一天

while (weekEnd.AddDays(1) <= monEnd)
{
i++;
//该周的开始时间
weekStart = weekEnd.AddDays(1);
//该周结束时间
weekEnd = weekEnd.AddDays(7) > monEnd ? monEnd : weekEnd.AddDays(7);

arrDate0[i - 1] = weekStart.ToString("yyyy-MM-dd 00:00:00");
arrDate1[i - 1] = weekEnd.ToString("yyyy-MM-dd 23:59:59");
// content += "第" + i + "周起始日期： " + weekStart.ToShortDateString() + "   结束日期： " + weekEnd.ToShortDateString() + "\n";
}

content += year + "年" + month + "月共有" + i + "周\n";
return Tuple.Create(DateTime.Parse(arrDate0[week.Value]), DateTime.Parse(arrDate1[week.Value]));
}

/// <summary>
/// 根据季度 获取开始时间和结束时间
/// </summary>
/// <param name="quarter">季度</param>
/// <returns></returns>
private Tuple<DateTime, DateTime> GetQurater(string quarter)
{
DateTime dt = new DateTime();
switch (quarter)
{
case "一季度":
dt = DateTime.Parse($"{DateTime.Now.Year},1, 01");
break;
case "二季度":
dt = DateTime.Parse($"{DateTime.Now.Year},4, 01");
break;
case "三季度":
dt = DateTime.Parse($"{DateTime.Now.Year},7, 01");
break;
case "四季度":
dt = DateTime.Parse($"{DateTime.Now.Year},10, 01");
break;

}

//本季度初
string start = dt.AddMonths(0 - (dt.Month - 1) % 3).AddDays(1 - dt.Day).ToString("yyyy-MM-01 00:00:00");  //本季度初
//获取本季度的最后一天
string end = dt.AddMonths(0 - (dt.Month - 1) % 3).AddDays(1 - dt.Day).AddMonths(3).AddDays(-1).ToString("yyyy-MM-dd 23:59:59"); ;  //

return Tuple.Create(DateTime.Parse(start), DateTime.Parse(end));
}