Weight randomized evergreen tweets by time since last sent in C#

gistfile1.txt

using System;
using System.Linq;

namespace WeightByTime
{
    record Tweet(long id, long time);

    static class UnixTime
    {
        public static long EpochTime(this DateTime dateTime) =>
            (long)dateTime.ToUniversalTime().Subtract(DateTime.UnixEpoch).TotalMilliseconds;

        public static long EpochTime(this string date) =>
            DateTime.Parse(date).EpochTime();
    }

    class Program
    {
        static readonly Random random = new();

        static void Main(string[] args)
        {
            var tweets = new Tweet[]
            {
                new Tweet(1, "3 Feb 2021 07:21:32 GMT".EpochTime()),
                new Tweet(2, "6 Feb 2021 12:31:46 GMT".EpochTime()),
                new Tweet(3, "19 Feb 2021 17:16:46 GMT".EpochTime()),
                new Tweet(4, "26 Feb 2021 06:14:26 GMT".EpochTime()),
                new Tweet(5, "2 Mar 2021 02:53:12 GMT".EpochTime()),
                new Tweet(6, "5 Mar 2021 17:27:34 GMT".EpochTime()),
                new Tweet(7, "6 Mar 2021 15:19:37 GMT".EpochTime()),
                new Tweet(8, "12 Mar 2021 18:22:37 GMT".EpochTime()),
                new Tweet(9, "17 Mar 2021 03:01:15 GMT".EpochTime()),
                new Tweet(10, "19 Mar 2021 14:12:13 GMT".EpochTime()),
            };

            for (int i = 0; i < 100; i++)
            {
                var weightedTweet = FindWeightedTweet(tweets);
                Console.WriteLine("Found " + weightedTweet);
            }
        }

        private static Tweet FindWeightedTweet(Tweet[] tweets)
        {
            var weights = tweets.Select(t => t.time);
            var min = weights.Min();
            var max = weights.Max() - min;
            var weightedTweets = tweets.Select(t => new Tweet(t.id, (max - (t.time - min)) / 1000));
            var totalWeights = weightedTweets.Select(t => t.time).Sum();
            var randomWeight = random.Next((int)totalWeights);
            var total = 0L;
            foreach (var tweet in weightedTweets)
            {
                total += tweet.time;
                if (total > randomWeight) return tweet;
            }
            return weightedTweets.Last();
        }
    }
}

According to the .NET System.Random documentation, if you don't ensure that the Random object is accessed in a thread-safe way, calls to methods that return random numbers return 0.

To make this threadsafe, replace line 19 with this:

        /// <summary>
        /// Static instance of random 
        /// </summary>
        /// <remarks>
        /// <see cref="https://docs.microsoft.com/en-us/dotnet/api/system.random?view=net-5.0#Multiple"/>
        /// </remarks>
        static readonly Random random = new();

        static object randomLocker = new object();

        /// <summary>
        /// Threadsafe call to random.Next
        /// </summary>
        /// <param name="max">Maximum value</param>
        /// <returns>Random number from 0 to max - 1</returns>
        static int Next(int max)
        {
            lock (randomLocker)
            {
                return random.Next(max);
            }
        }

and line 72 with this:

            var randomWeight = Next((int)totalWeights);