#if INTERACTIVE
#r "WindowsBase.dll"
#r "PresentationCore.dll"
#r "PresentationFramework.dll"
#endif

open System.Windows
open System.Windows.Input

let getLocation (element : #IInputElement) (args : #MouseEventArgs) =
  let position = args.GetPosition element
  position.X, position.Y

let getMouseClicks (element : #IInputElement) =
  let mouseDowns = element.MouseLeftButtonDown |> Event.map (fun _ -> true)
  let mouseUps   = element.MouseLeftButtonUp   |> Event.map (fun _ -> false)
  mouseDowns |> Event.merge mouseUps

let getMouseDiffs (element : #IInputElement) =
  let mouseMoves = element.MouseMove |> Event.map (getLocation element)
  mouseMoves
  |> Event.zip mouseMoves
  |> Event.map (fun ((fstX, fstY), (sndX, sndY)) -> fstX - sndX, fstY - sndY)

let getMouseDrag (element : #IInputElement) =
  getMouseClicks element
  |> Event.collect (fun leftDown ->
       printfn "Left down %b" leftDown
       getMouseDiffs element
       |> Event.filter (fun _ -> printfn "Inner Left down %b" leftDown; leftDown))

let getMouseDrag' (element : #IInputElement) =
  let event = new Event<_>()
  let ok = ref false
  getMouseClicks element |> Event.add (fun arg -> ok := arg)
  getMouseDiffs  element
    |> Event.add (fun arg -> if !ok then event.Trigger arg)
  event.Publish