Agent for countdown

authentication.fs

    module private CountdownExpiryAgent =
        open Modal

        type Operation =
            | Reset of remainingSecs: int
            | Tick
            | RegisterHandler of logout: (unit -> unit)

        let agent (rv: Var<int>) courtesy = 
            MailboxProcessor.Start(fun inbox -> 
                let rec loop state: Async<unit>  =
                    let (rvCountdown, logout) = state
                    async {
                        let! msg = inbox.Receive()

                        match msg with
                        | Reset time ->
                            Var.Set rvCountdown time
                            return! loop (rvCountdown, logout)
                        | Tick ->
                            if rvCountdown.Value = courtesy then
                                JQuery.Of("#courtesyExpiryModal").ModalShow() |> ignore

                            if rvCountdown.Value = 0 then
                                do logout |> Option.iter(fun act -> act())
                                return! loop (rvCountdown, logout)
                            else
                                Var.Set rvCountdown (rvCountdown.Value - 1)
                                Console.Log rvCountdown.Value
                                return! loop (rvCountdown, logout)
                    
                        | RegisterHandler (logout) ->
                            return! loop (rvCountdown, Some logout)
                            
                    }
                loop (rv, None))

        let startTick (agent: MailboxProcessor<Operation>) =
            async {
                while true do
                    do! Async.Sleep 1000
                    do agent.Post Operation.Tick
            } |> Async.Start
        
        let countdown = Var.Create 0

        let post =
            let lifetime =
                match TokenStorage.get(), TokenStorage.getTimeStamp()  with
                    | Some token, Some stamp ->
                        let payload = Jwt.getPayload token
                        match payload.exp - payload.iat with
                            // Target time is already passed, the token is expired
                            | lifetime when Jwt.JwtPayload.GetTimeTarget stamp payload < 0 ->
                                Console.Log "Token expired."; 0
                    
                            | lifetime -> lifetime
                    | _ -> 
                        Console.Log "Token not found."; 0
            Var.Set countdown lifetime
            let courtesyWindow = 60
            let agent = agent countdown courtesyWindow
            startTick agent
            agent.Post

authentication1.fs

let run() = 
        let modalOptions =
            { Id = "courtesyExpiryModal"
              Title = "Your session is about to expire"
              Content = div [ p [ text "Your secure session to this web portal is close to expiring."; br []; text "Please indicate whether you would prefer to remain logged in?" ]
                              p [ CountdownExpiryAgent.countdown.View |> View.Map (sprintf "Time remaining: %i seconds") |> Doc.TextView ] ]
              PositiveAction = Title "Keep me logged in", Action (fun () -> renewToken() |> Async.Ignore)
              NegativeAction = Title "Log out", Action (fun () -> async { do logout() }) }

        Modal.createModal modalOptions
        CountdownExpiryAgent.post (CountdownExpiryAgent.RegisterHandler logout)
        Doc.Empty

do CountdownExpiryAgent.post (CountdownExpiryAgent.Reset 120)