Refactoring to have a greater separation of concern.

MongoDbGenericRepository/Utils/RandomExtensions.cs

@@ -0,0 +1,60 @@
+using System;
+
+namespace MongoDbGenericRepository.Utils
+{
+    // Thanks BlueRaja - Danny Pflughoeft https://stackoverflow.com/a/13095144/5103354
+    /// <summary>
+    /// Extensions for the random number generator <see cref="Random"/>
+    /// </summary>
+    public static class RandomExtensions
+    {
+        /// <summary>
+        /// Returns a random long from min (inclusive) to max (exclusive)
+        /// </summary>
+        /// <param name="random">The given random instance</param>
+        /// <param name="min">The inclusive minimum bound</param>
+        /// <param name="max">The exclusive maximum bound.  Must be greater than min</param>
+        public static long NextLong(this Random random, long min, long max)
+        {
+            if (max <= min)
+                throw new ArgumentOutOfRangeException("max", "max must be > min!");
+
+            //Working with ulong so that modulo works correctly with values > long.MaxValue
+            ulong uRange = (ulong)(max - min);
+
+            //Prevent a modulo bias; see https://stackoverflow.com/a/10984975/238419
+            //for more information.
+            //In the worst case, the expected number of calls is 2 (though usually it's
+            //much closer to 1) so this loop doesn't really hurt performance at all.
+            ulong ulongRand;
+            do
+            {
+                byte[] buf = new byte[8];
+                random.NextBytes(buf);
+                ulongRand = (ulong)BitConverter.ToInt64(buf, 0);
+            } while (ulongRand > ulong.MaxValue - ((ulong.MaxValue % uRange) + 1) % uRange);
+
+            return (long)(ulongRand % uRange) + min;
+        }
+
+        /// <summary>
+        /// Returns a random long from 0 (inclusive) to max (exclusive)
+        /// </summary>
+        /// <param name="random">The given random instance</param>
+        /// <param name="max">The exclusive maximum bound.  Must be greater than 0</param>
+        public static long NextLong(this Random random, long max)
+        {
+            return random.NextLong(0, max);
+        }
+
+        /// <summary>
+        /// Returns a random long over all possible values of long (except long.MaxValue, similar to
+        /// random.Next())
+        /// </summary>
+        /// <param name="random">The given random instance</param>
+        public static long NextLong(this Random random)
+        {
+            return random.NextLong(long.MinValue, long.MaxValue);
+        }
+    }
+}