As continuation for my previous post I want to create a daemon which runs jobs using created cron code.

module Daemon =
    [<Literal>]
    let INTERVAL = 30000

    let internalRun interval (now: unit->DateTime) (jobs: seq<Job>) =
        // to dispose System.Threading.Timer properly
        let createDisposable f =
            {
                new IDisposable with
                    member x.Dispose() = f()
            }

        // event fot Timer
        let timerElapsed obj =
            let checkJob = () |> now |> Schedule.isTime
            jobs
            |> Seq.map (fun x ->
                let schedule = Schedule.generate x.cron
                (schedule, x.action)
            )
            |> Seq.filter (fun (x, y) -> checkJob x)
            |> Seq.map (fun (x, y) -> y)
            |> Async.Parallel
            |> Async.RunSynchronously
            |> ignore

        // timer
        let localTimer = new Timer(timerElapsed, null, Timeout.Infinite, interval)
        // start timer
        localTimer.Change(0, interval) |> ignore
        // return timer as IDisposable
        createDisposable (fun() -> localTimer.Dispose())

    // get DateTime
    let now = fun () -> DateTime.UtcNow
    // public method to call
    let run jobs = internalRun INTERVAL now jobs

How to use the daemon above:

type Job = { action: Async<unit>; cron: string }

let act id =
    async {
        printfn "Execution %A" id
    }
let jobs = [|1; 2|] |> Array.map (fun id ->
    {
        action = act id;
        cron = "* * * * *"
    })
let daemon = run jobs

Unfortunately I don’t see the good way to wtite unit test for this code as there is hardcoded dependency to System.Threading.Timer.

Feel free to comment if you see the solution. Thanks in advance.