Extension methods for converting DateTime to Epoch.

using System;

namespace MyNameSpace
{
    public static class EpochDateTimeExtensions
    {
        /// <summary>
        /// Converts the given date value to epoch time.
        /// </summary>
        /// <remarks>
        /// https://raw.githubusercontent.com/IdentityModel/Thinktecture.IdentityModel/master/source/Core/Extensions/DateTimeExtensions.cs
        /// </remarks>
        public static long ToEpochTime(this DateTime dateTime)
        {
            var date = dateTime.ToUniversalTime();
            var ticks = date.Ticks - new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc).Ticks;
            var ts = ticks / TimeSpan.TicksPerSecond;
            return ts;
        }

        /// <summary>
        /// Converts the given date value to epoch time.
        /// </summary>
        public static long ToEpochTime(this DateTimeOffset dateTime)
        {
            var date = dateTime.ToUniversalTime();
            var ticks = date.Ticks - new DateTimeOffset(1970, 1, 1, 0, 0, 0, TimeSpan.Zero).Ticks;
            var ts = ticks / TimeSpan.TicksPerSecond;
            return ts;
        }

        /// <summary>
        /// Converts the given epoch time to a <see cref="DateTime"/> with <see cref="DateTimeKind.Utc"/> kind.
        /// </summary>
        public static DateTime ToDateTimeFromEpoch(this long intDate)
        {
            var timeInTicks = intDate * TimeSpan.TicksPerSecond;
            return new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc).AddTicks(timeInTicks);
        }

        /// <summary>
        /// Converts the given epoch time to a UTC <see cref="DateTimeOffset"/>.
        /// </summary>
        public static DateTimeOffset ToDateTimeOffsetFromEpoch(this long intDate)
        {
            var timeInTicks = intDate * TimeSpan.TicksPerSecond;
            return new DateTimeOffset(1970, 1, 1, 0, 0, 0, TimeSpan.Zero).AddTicks(timeInTicks);
        }
    }
}