C# 计算 指定年第几周，加减N周后时间范围

Code

        /// <summary>
        /// 计算 指定年第几周，加减N周后时间范围
        /// </summary>
        /// <param name="year">指定年</param>
        /// <param name="week">第几周</param>
        /// <param name="weekDiffNum">加减N周</param>
        [Theory]
        [InlineData(2022, 2, -2)]
        [InlineData(2023, 2, -2)]
        [InlineData(2023, 3, 1)]
        [InlineData(2023, 4, -2)]
        public void CalcWeekDiff(int year, int week, int weekDiffNum)
        {
            //  今年第一天
            var firstDay = new DateTime(year, 1, 1);
            //  今年第一周的最后一天 = 6（礼拜天是0，礼拜六是6） - 当前天是本周第几天
            var firstWeekLastDay = firstDay.AddDays(6 - (int)firstDay.DayOfWeek);
            TestOutputHelper.WriteLine($"year:{year}\t第一天:{firstDay.ToShortString()}\t在第一周中属于第几天:{(int)firstDay.DayOfWeek}\tRange:[{firstWeekLastDay.AddDays(-6).ToShortString()} => {firstWeekLastDay.ToShortString()}]");
            //  得到指定周最后一天
            var specifyDate = firstWeekLastDay.AddDays((week - 1) * 7);
            TestOutputHelper.WriteLine($"第[{week}]周\tRange:[{specifyDate.AddDays(-6).ToShortString()} => {specifyDate.ToShortString()}]");
            //  计算指定周后的范围
            var calcDiffDate = specifyDate.AddDays(weekDiffNum * 7);
            TestOutputHelper.WriteLine($"操作[{weekDiffNum}]周\tRange:[{calcDiffDate.AddDays(-6).ToShortString()} => {calcDiffDate.ToShortString()}]");
        }

Result

year:2022    第一天:2022-01-01    在第一周中属于第几天:6    Range:[2021-12-26 => 2022-01-01]
第[2]周    Range:[2022-01-02 => 2022-01-08]
操作[-2]周    Range:[2021-12-19 => 2021-12-25]