nextleet.elm

module Main exposing (..)

import Html exposing (Html)
import Html.App as App
import Time exposing (Time, second)
import Date exposing (Date)
import Date.Extra as Dx


main : Program Never
main =
    App.program
        { init = init
        , view = view
        , update = update
        , subscriptions = subscriptions
        }



-- MODEL


type alias Model =
    Time


init : ( Model, Cmd Msg )
init =
    ( 0, Cmd.none )



-- UPDATE


type Msg
    = Tick Time


update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        Tick newTime ->
            ( newTime, Cmd.none )



-- SUBSCRIPTIONS


subscriptions : Model -> Sub Msg
subscriptions model =
    Time.every second Tick



-- VIEW


view : Model -> Html Msg
view model =
    let
        now =
            Date.fromTime model

        target =
            nextMomentFrom 13 37 now

        diff =
            Dx.diff Dx.Second now target
    in
        Html.div []
            [ Html.div [] [ Html.text <| toString now ]
            , Html.div [] [ Html.text <| toString target ]
            , Html.div [] [ Html.text <| toString diff ]
            ]


nextMomentFrom : Int -> Int -> Date -> Date
nextMomentFrom h m from =
    let
        sameDayTarget =
            Dx.floor Dx.Day from |> Dx.add Dx.Hour h |> Dx.add Dx.Minute m
    in
        if Dx.compare sameDayTarget from == LT then
            sameDayTarget |> Dx.add Dx.Day 1
        else
            sameDayTarget

Using justinmimbs/elm-date-extra