namespace Admin.NET.Plugin.AiDOP.Infrastructure.S8;

/// <summary>
/// 首版按服务器自然周期对齐大屏统计口径；显式日期范围优先于 period。
/// </summary>
public static class S8PeriodHelper
{
    /// <summary>
    /// 将 period 字符串解析为半开区间 [from, to)。
    /// 支持 today / this_week / this_month（大小写容错）。
    /// 非法或空值返回 (null, null)，调用方保持全量行为。
    /// </summary>
    public static (DateTime? from, DateTime? to) Resolve(string? period)
    {
        if (string.IsNullOrWhiteSpace(period)) return (null, null);

        var today = DateTime.Today;
        return period.Trim().ToLowerInvariant() switch
        {
            "today" => (today, today.AddDays(1)),
            "this_week" => ResolveThisWeek(today),
            "this_month" => (new DateTime(today.Year, today.Month, 1), new DateTime(today.Year, today.Month, 1).AddMonths(1)),
            _ => (null, null),
        };
    }

    private static (DateTime? from, DateTime? to) ResolveThisWeek(DateTime today)
    {
        // 周一作为周起始（DayOfWeek.Monday = 1）
        var offset = ((int)today.DayOfWeek - (int)DayOfWeek.Monday + 7) % 7;
        var monday = today.AddDays(-offset);
        return (monday, monday.AddDays(7));
    }
}