// 1) Create TransactionScope, on Mono and in .NET, and the later one supports TransactionScopeAsyncFlowOption.
// 2) Then, complete the transaction automatically if no exceptions has been thrown.
// If Async or Task, then automatically await the result before complete without blocking the thread.

#if INTERACTIVE
#r "System.Transactions.dll"
#endif
open System
open System.Threading
open System.Threading.Tasks
open System.Transactions

let logmsg act threadid transId =
    let tidm = match String.IsNullOrEmpty threadid with | true -> "" | false -> " at thread " + threadid
    let msg = "Transaction " + transId + " " + act + tidm
    Console.WriteLine msg
    //Logary.Logger.log (Logary.Logging.getCurrentLogger()) (Logary.Message.eventDebug msg) |> start

let getTransactionId() =
    match Transaction.Current <> null && Transaction.Current.TransactionInformation <> null with
    | true -> Transaction.Current.TransactionInformation.LocalIdentifier
    | false -> ""

let transactionWithManualComplete<'T>() =
    match Type.GetType ("Mono.Runtime") <> null with
    | true -> new Transactions.TransactionScope()
    | false ->
        // Mono would fail to compilation, so we have to construct this via reflection:
        // new Transactions.TransactionScope(Transactions.TransactionScopeAsyncFlowOption.Enabled)
        let transactionAssembly = System.Reflection.Assembly.GetAssembly typeof<TransactionScope>
        let asynctype = transactionAssembly.GetType "System.Transactions.TransactionScopeAsyncFlowOption"
        let transaction = typeof<TransactionScope>.GetConstructor [|asynctype|]
        transaction.Invoke [|1|] :?> TransactionScope

let transactionWith<'T> (func: unit -> 'T) =
    use scope = transactionWithManualComplete()
    let transId = getTransactionId()
    logmsg "started" Thread.CurrentThread.Name transId
    let res = func()
    match box res with
    | :? Task as task -> 
        let commit = Action<Task>(fun a -> 
            logmsg "completed" Thread.CurrentThread.Name transId
            scope.Complete()
            )
        let commitTran1 = task.ContinueWith(commit, TaskContinuationOptions.OnlyOnRanToCompletion)
        let commitTran2 = task.ContinueWith((fun _ -> 
            logmsg "failed" Thread.CurrentThread.Name transId), TaskContinuationOptions.NotOnRanToCompletion)
        res
    | item when item <> null && item.GetType().Name = "FSharpAsync`1" ->
        let msg = "Use transactionWithAsync"
        //Logary.Logger.log (Logary.Logging.getCurrentLogger()) (Logary.Message.eventError msg) |> start
        failwith msg 
    | _ -> 
        logmsg "completed" System.Threading.Thread.CurrentThread.Name transId
        scope.Complete()
        res

let transactionWithAsync<'T> (func: unit -> Async<'T>) =
    async {
        use scope = transactionWithManualComplete()
        let transId = getTransactionId()
        logmsg "started" Thread.CurrentThread.Name transId
        let! res = func()
        logmsg "completed" Thread.CurrentThread.Name transId
        scope.Complete()
        return res
    }

(*
let ``example usage`` =
    transactionWith <| fun () -> 
        Console.WriteLine "Normal source code in transaction"
        Console.WriteLine "e.g. database operations!"
        Console.WriteLine "Return values and "
        Console.WriteLine "C# Task classes supported."

let ``example usage FSharpAsync`` =
    transactionWithAsync <| fun () -> async {
        Console.WriteLine "Async source code in transaction"
        return "hello!"
    }
exampleusageFSharpAsync |> Async.RunSynchronously;;
*)