C# DateTime 扩展类 常用方法

    /// <summary>
    /// Extension methods for <see cref="DateTime"/>.
    /// </summary>
    public static class DateTimeExtensions
    {
   
        /// <summary>
        /// Converts a DateTime to a Unix Timestamp
        /// </summary>
        /// <param name="target">This DateTime</param>
        /// <returns></returns>
        public static double ToUnixTimestamp(this DateTime target)
        {
   
            var origin = new DateTime(1970, 1, 1, 0, 0, 0, 0);
            var diff = target - origin;
            return Math.Floor(diff.TotalSeconds);
        }

        /// <summary>
        /// Converts a Unix Timestamp in to a DateTime
        /// </summary>
        /// <param name="unixTime">This Unix Timestamp</param>
        /// <returns></returns>
        public static DateTime FromUnixTimestamp(this double unixTime)
        {
   
            var epoch = new DateTime(1970, 1, 1, 0, 0, 0, 0);
            return epoch.AddSeconds(unixTime);
        }

        /// <summary>
        /// Gets the value of the End of the day (23:59)
        /// </summary>
        /// <param name="target"></param>
        /// <returns></returns>
        public static DateTime ToDayEnd(this DateTime target)
        {
   
            return target.Date.AddDays(1).AddMilliseconds(-1);
        }

        /// <summary>
        /// Gets the First Date of the week for the specified date
        /// </summary>
        /// <param name="dt">this DateTime</param>
        /// <param name="startOfWeek">The Start Day of the Week (ie, Sunday/Monday)</param>
        /// <returns>The First Date of the week</returns>
        public static DateTime StartOfWeek(this DateTime dt, DayOfWeek startOfWeek)
        {
   
            var diff = dt.DayOfWeek - startOfWeek;

            if (diff < 0)
                diff += 7;

            return dt.AddDays(-1 * diff).Date;