Add support to reading backwards by changing ReadVersion type

Author: Jamil Maqdis Anton

src/Read.fs

@@ -4,7 +4,11 @@ open System.Threading
 open SqlStreamStore.Streams
 
 module Read =
-    let private fromReadVersion: uint -> int = fun readVersion -> int (readVersion)
+    let private fromReadVersion: ReadVersion -> int =
+        function
+        | ReadVersion.Start -> int (Position.Start)
+        | ReadVersion.End -> int (Position.End)
+        | ReadVersion.SpecificVersion version -> int (version)
 
     let readFromAllStream: SqlStreamStore.IStreamStore -> ReadingDirection -> StartPositionInclusive -> MessageCount -> Async<ReadAllPage> =
         fun store readingDirection startPositionInclusive msgCount ->

src/Types.fs

@@ -13,15 +13,19 @@ type MessageDetails =
 
 type StreamName = string
 
+[<RequireQualifiedAccessAttribute>]
+type ReadVersion =
+     | Start
+     | End
+     | SpecificVersion of uint
+
 [<RequireQualifiedAccessAttribute>]
 type AppendVersion =
     | Any
     | EmptyStream
     | NoStream
     | SpecificVersion of int
 
-and ReadVersion = uint
-
 type StartPositionInclusive = int64
 type MessageCount = int
 

tests/ReadTests.fs

@@ -37,7 +37,7 @@ let tests =
               do! Append.appendNewMessages inMemStore streamName appendVersion msgList
                   |> Async.Ignore
 
-              let readVersion = 0u
+              let readVersion = ReadVersion.Start
 
               let! readResult = Read.readFromStream inMemStore ReadingDirection.Forward streamName readVersion 10
 
@@ -46,4 +46,42 @@ let tests =
               |> fun sorted ->
                   ExpectExtra.equal guidString1 (sorted.[0].MessageId.ToString())
                   ExpectExtra.equal guidString2 (sorted.[1].MessageId.ToString())
+          }
+          testAsync "Should read Backward from specific stream." {
+              let inMemStore = new SqlStreamStore.InMemoryStreamStore()
+
+              let streamName = "test"
+
+              let appendVersion = AppendVersion.NoStream
+
+              let guidString1 = "11111111-1111-1111-1111-111111111111"
+
+              let guidString2 = "22222222-2222-2222-2222-222222222222"
+
+              let msg1 =
+                  { id = StreamMessageId.Custom(System.Guid.Parse(guidString1))
+                    type_ = "testing"
+                    jsonData = "{}"
+                    jsonMetadata = "{}" }
+
+              let msg2 =
+                  { id = StreamMessageId.Custom(System.Guid.Parse(guidString2))
+                    type_ = "testing"
+                    jsonData = "{}"
+                    jsonMetadata = "{}" }
+
+              let msgList = [ msg1; msg2 ]
+
+              do! Append.appendNewMessages inMemStore streamName appendVersion msgList
+                  |> Async.Ignore
+
+              let readVersion = ReadVersion.End
+
+              let! readResult = Read.readFromStream inMemStore ReadingDirection.Backward streamName readVersion 10
+
+              readResult.Messages
+              |> Array.sortBy (fun msg -> msg.MessageId)
+              |> fun sorted ->
+                  ExpectExtra.equal guidString2 (sorted.[1].MessageId.ToString())
+                  ExpectExtra.equal guidString1 (sorted.[0].MessageId.ToString())
           } ]