selfcheckout.elm

import Signal
import Graphics.Element exposing (..)
import Graphics.Input exposing (..)
import Graphics.Input.Field exposing (..)
import List
import String
import Window
import Task exposing (Task)
import Text
import Keyboard

type alias Item = Float
type alias Model = { items : List Item
                   , receipt : String
                   , field : Content
                   , windowSize : (Int, Int)
                   }

type Action = Reset
            | ScanItem
            | UndoScan
            | UpdateField Content
            | UpdateWindowSize (Int, Int)

model : Signal Model
model =
  Signal.foldp
    update
    emptyModel
    (Signal.merge actions.signal <| Signal.filterMap (\x -> if x then Just ScanItem else Nothing) Reset Keyboard.enter)

actions : Signal.Mailbox Action
actions = Signal.mailbox Reset

main =
  Signal.map view model

view : Model -> Element
view model =
  let windowWidth = fst model.windowSize
      windowHeight = snd model.windowSize
      centeredContainer = \value -> container windowWidth (heightOf value) middle value
      visualElements =
        [ "You're buying $" ++ toString (List.sum model.items) ++ " worth of junk, " ++ toString (List.length model.items) ++ " items in total"
          |> Text.fromString
          |> centered
          |> centeredContainer
        , field defaultStyle (UpdateField >> Signal.message actions.address) "Item Cost" model.field
          |> centeredContainer
        , button (Signal.message actions.address ScanItem) "Add Item"
          |> height 20
          |> centeredContainer
        ]
        |> List.intersperse (spacer 20 20)
  in
    visualElements
    ++
    [ button (Signal.message actions.address UndoScan) "Undo Last Scan"
      |> height 20
      |> centeredContainer
    ]
    |> flow down

emptyModel : Model
emptyModel = { items = []
             , receipt = ""
             , field = noContent
             , windowSize = (0,0)
             }

update : Action -> Model -> Model
update action model =
  case action of
    Reset ->
      { emptyModel
      | windowSize = model.windowSize
      }
    ScanItem ->
      case String.toFloat model.field.string of
        Ok item -> { model
                   | items = model.items ++ [item]
                   , field = noContent
                   }
        Err _ -> { model
                 | field = noContent
                 }
    UndoScan ->
      { model
      | items = List.reverse <| List.drop 1 <| List.reverse model.items
      }
    UpdateField f ->
      { model
      | field = f
      }
    UpdateWindowSize s ->
      { model
      | windowSize = s
      }

port windowSizeUpdate : Signal (Task x ())
port windowSizeUpdate =
  Signal.map UpdateWindowSize Window.dimensions
  |> Signal.map (Signal.send actions.address)