refactor: clean up logic a little bit

repository just passes in previous version and next version, method will do the math so that it only has to exist in one location

Author: the-avid-engineer

src/EntityDb.Common/Exceptions/OptimisticConcurrencyException.cs

@@ -7,8 +7,8 @@ namespace EntityDb.Common.Exceptions
     /// <summary>
     ///     The exception that is logged when an actor passes a <see cref="ITransaction{TEntity}" /> to an
     ///     <see cref="ITransactionRepository{TEntity}" /> with a
-    ///     <see cref="ITransactionCommand{TEntity}.ExpectedPreviousVersionNumber" /> unequal to the actual previous version
-    ///     number.
+    ///     <see cref="ITransactionCommand{TEntity}.EntityVersionNumber" /> that is not the next number
+    ///     after the previous version number.
     /// </summary>
     /// <remarks>
     ///     A program will not be able to catch this exception if it is thrown.
@@ -18,14 +18,14 @@ namespace EntityDb.Common.Exceptions
     public sealed class OptimisticConcurrencyException : Exception
     {
         /// <summary>
-        ///     Throws a new <see cref="OptimisticConcurrencyException" /> if <paramref name="expectedPreviousVersionNumber" /> is
-        ///     not equal to <paramref name="actualPreviousVersionNumber" />.
+        ///     Throws a new <see cref="OptimisticConcurrencyException" /> if <paramref name="nextVersionNumber" />
+        ///     is not the next number after <paramref name="previousVersionNumber" />.
         /// </summary>
-        /// <param name="expectedPreviousVersionNumber"></param>
-        /// <param name="actualPreviousVersionNumber"></param>
-        public static void ThrowIfMismatch(ulong expectedPreviousVersionNumber, ulong actualPreviousVersionNumber)
+        /// <param name="previousVersionNumber">The previous version number.</param>
+        /// <param name="nextVersionNumber">The next version number.</param>
+        public static void ThrowIfDiscontinuous(ulong previousVersionNumber, ulong nextVersionNumber)
         {
-            if (expectedPreviousVersionNumber != actualPreviousVersionNumber)
+            if (nextVersionNumber != previousVersionNumber + 1)
             {
                 throw new OptimisticConcurrencyException();
             }

src/EntityDb.MongoDb/Transactions/MongoDbTransactionRepository.cs

@@ -92,13 +92,13 @@ await SourceDocument.InsertOne(clientSessionHandle, mongoDatabase,
 
                     foreach (var transactionCommand in transaction.Commands)
                     {
-                        var actualPreviousVersionNumber =
+                        VersionZeroReservedException.ThrowIfZero(transactionCommand.EntityVersionNumber);
+                        
+                        var previousVersionNumber =
                             await CommandDocument.GetLastEntityVersionNumber(clientSessionHandle, mongoDatabase,
                                 transactionCommand.EntityId);
 
-                        VersionZeroReservedException.ThrowIfZero(transactionCommand.EntityVersionNumber);
-                        OptimisticConcurrencyException.ThrowIfMismatch(transactionCommand.EntityVersionNumber - 1,
-                            actualPreviousVersionNumber);
+                        OptimisticConcurrencyException.ThrowIfDiscontinuous(previousVersionNumber, transactionCommand.EntityVersionNumber);
 
                         await CommandDocument.InsertOne(clientSessionHandle, mongoDatabase,
                             CommandDocument.BuildOne(logger, transaction, transactionCommand));