using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    public static void Main()
    {
        // 示例数据：日期和对应的值
        var data = new List<DataItem>
        {
            new DataItem { Date = new DateTime(2023, 1, 1), Value = 10 },
            new DataItem { Date = new DateTime(2023, 1, 2), Value = 20 },
            new DataItem { Date = new DateTime(2023, 1, 8), Value = 30 },
            new DataItem { Date = new DateTime(2023, 1, 9), Value = 40 },
            new DataItem { Date = new DateTime(2023, 1, 15), Value = 50 },
            new DataItem { Date = new DateTime(2023, 1, 16), Value = 60 },
            new DataItem { Date = new DateTime(2023, 1, 22), Value = 70 },
            new DataItem { Date = new DateTime(2023, 1, 23), Value = 80 },
        };

        // 按每7天分组并求和
        var result = data.GroupBy(
            item => (item.Date - data.Min(d => d.Date)).Days / 7, // 计算周数
            (week, items) => new 
            {
                WeekNumber = week,
                StartDate = items.Min(i => i.Date),
                EndDate = items.Max(i => i.Date),
                TotalValue = items.Sum(i => i.Value)
            })
            .OrderBy(g => g.WeekNumber)
            .ToList();

        // 输出结果
        foreach (var group in result)
        {
            Console.WriteLine($"Week {group.WeekNumber + 1}: {group.StartDate:yyyy-MM-dd} to {group.EndDate:yyyy-MM-dd}, Total: {group.TotalValue}");
        }
    }
}

public class DataItem
{
    public DateTime Date { get; set; }
    public int Value { get; set; }
}

var referenceDate = new DateTime(2023, 1, 1); // 自定义参考日期
var result = data.GroupBy(
    item => (item.Date - referenceDate).Days / 7,
    // 其余代码相同