Add this to Route.href to prevent click but not Cmd or middle clicks

[wking-io]

https://github.com/elm-lang/html/issues/110

[wking-io]

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        NewLocation location ->
            let
                newRoute =
                    parseLocation location
            in
                { model | page = newRoute } ! []

        NewPage page ->
            model ! [ Navigation.newUrl (Routing.pageToUrl page) ]

href : ( Route -> Cmd Msg) -> Route -> List (Attribute Msg)
href msg route =
    [ href (routeToString route)
    , onPreventDefaultClick (msg route)
    ]


onPreventDefaultClick : msg -> Attribute msg
onPreventDefaultClick message =
    onWithOptions "click"
        { defaultOptions | preventDefault = True }
        (preventDefault2
            |> Json.Decode.andThen (maybePreventDefault message)
        )


preventDefault2 : Decoder Bool
preventDefault2 =
    Json.Decode.map2
        (invertedOr)
        (Json.Decode.field "ctrlKey" Json.Decode.bool)
        (Json.Decode.field "metaKey" Json.Decode.bool)


maybePreventDefault : msg -> Bool -> Decoder msg
maybePreventDefault msg preventDefault =
    case preventDefault of
        True ->
            Json.Decode.succeed msg

        False ->
            Json.Decode.fail "Normal link"


invertedOr : Bool -> Bool -> Bool
invertedOr x y =
    not (x || y)