DownloadManager.elm

-- Only works with Elm 0.15
import Html
import Task
import Port
import Debug
import Dict
import Time

-- MODEL

type alias DownloadId = Int

type alias Progress = Int

type alias Download =
  { filename: String
  , percent: Progress
  }

type alias Model = 
  { order: List DownloadId
  , downloads: Dict.Dict DownloadId Download
  }

initialModel : Model
initialModel =
  { order = [ 1, 2 ]
  , downloads = Dict.empty
      |> Dict.insert 1 {filename = "cats.jpg", percent = 0 }
      |> Dict.insert 2 {filename = "hats.jpg", percent = 50}
  }

-- UPDATE

type Action
  = UpdateDownload DownloadId Progress

updateProgress : Progress -> Download -> Download
updateProgress percent download = { download | percent <- percent }

updateDownload : (Download -> Download) -> DownloadId -> Model -> Model
updateDownload fn id model =
  { model | downloads <- Dict.update id (Maybe.map fn) model.downloads }

step : Action -> Model -> Model
step action = case action of
  UpdateDownload id progress ->
    updateDownload (updateProgress progress) id

-- RENDERING

downloadToString : Download -> String
downloadToString d = (d.filename ++ " (" ++ (toString d.percent) ++ "%)")

scene : Model -> Html.Html
scene model = 
  model.order
  |> List.map (\id -> Html.li []
    [ model.downloads
      |> Dict.get id
      |> Maybe.map downloadToString
      |> Maybe.map Html.text
      |> Maybe.withDefault (Html.text "BAD")
    ])
  |> Html.ul []

-- PORTS

port results : Port.Port Action

update : DownloadId -> Time.Time -> Progress -> Task.Task () (List ())
update id t percent =
  Task.sequence
    [ Task.sleep t
    , Port.send results.address (UpdateDownload id percent)
    ]

-- WIRING

model : Varying Model
model = Stream.fold step initialModel results.stream

main : Varying Html.Html
main = Varying.map scene model

perform
  Task.sequence <|
    List.map (uncurry (update 1)) <|
    [ (500, 10)
    , (500, 24)
    , (200, 42)
    , (300, 64)
    , (800, 95)
    , (100, 100)
    ]

perform
  Task.sequence <|
    List.map (uncurry (update 2)) <|
    [ (900, 52)
    , (200, 53)
    , (100, 54)
    , (100, 55)
    , (500, 60)
    , (100, 63)
    , (100, 68)
    , (100, 71)
    , (100, 73)
    , (100, 77)
    , (100, 79)
    , (100, 81)
    ]