DropDown.elm

module Page.Helper.Dropdown exposing (Dropdown, Msg(..), init, isDroppedDown, itemHasBeenClicked, update)

-- TYPES


type Dropdown
    = Internal { show : Bool, itemClicked : Bool }


init : Dropdown
init =
    Internal { show = False, itemClicked = False }



-- INFO


itemHasBeenClicked : Dropdown -> Bool
itemHasBeenClicked (Internal status) =
    status.itemClicked


isDroppedDown : Dropdown -> Bool
isDroppedDown (Internal status) =
    status.show



-- UPDATE


type Msg
    = ItemMouseDown
    | LostFocus
    | ToggleShow


update : Msg -> Dropdown -> Dropdown
update msg (Internal status) =
    case msg of
        ItemMouseDown ->
            Internal { status | itemClicked = True }

        LostFocus ->
            if status.itemClicked then
                Internal status

            else
                Internal { status | show = False }

        ToggleShow ->
            Internal
                { status
                    | show = not status.show
                    , itemClicked = False
                }

Main.elm

import Page.Helper.Dropdown as Dropdown

type Msg
    = GotMenuMsg Dropdown.Msg

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case ( msg, model ) of
        ( GotMenuMsg subMsg, _ ) ->
            let
                subModel =
                    Dropdown.update subMsg (Session.menu (toSession model))
            in
            ( mapSessionConfig (\c -> { c | menu = subModel }) model
            , Cmd.none
            )


view : Model -> Document Msg
view model =
    let
        viewPage page toMsg config =
            let
                { title, body } =
                    Page.view GotMenuMsg (Session.viewer (toSession model)) page config
            in
            { title = title
            , body = List.map (Html.map toMsg) body
            }

Page.elm

import Page.Helper.Dropdown as Dropdown

view : (Dropdown.Msg -> msg) -> Session -> { title : String, content : Element msg } -> Document msg
view menuMsg session { title, content, modal } =

Session.elm

import Page.Helper.Dropdown as Dropdown exposing (Dropdown)

type Session
    = Guest Nav.Key Config


type alias Config =
    { menu : Dropdown
    }
    

menu : Session -> Dropdown
menu =
    .menu << config

config : Session -> Config
config session =
    case session of
        Guest _ conf ->
            conf