using System;

namespace BF
{
	public static class TimeHelper
	{
		public static long GetDayBeginTimestamp(long timestamp, int timeZoneOffset)
		{
			// 将时间戳转换为UTC时间
			DateTime utcTime = DateTimeOffset.FromUnixTimeSeconds(timestamp).UtcDateTime;
			// 应用时区偏移（不考虑夏令时）
			if (timeZoneOffset != 0)
			{
				utcTime = utcTime.AddHours(timeZoneOffset);
			}
			// 构造当天0点的UTC时间
			DateTime utcDayBegin = new DateTime(utcTime.Year, utcTime.Month, utcTime.Day, 0, 0, 0, DateTimeKind.Utc);
			// 减去时区偏移量恢复UTC时间
			if (timeZoneOffset != 0)
			{
				utcDayBegin = utcDayBegin.AddHours(-timeZoneOffset);
			}
			// 转换为时间戳并减去时区偏移
			long utcDayBeginTimestamp = new DateTimeOffset(utcDayBegin).ToUnixTimeSeconds();
			return utcDayBeginTimestamp;
		}
	}
}