type Model =
    Model Iso8601Base

type alias Iso8601Base =
    { offsetInMinutes : Maybe Int
    , date : Iso8601DateOption
    , time : Maybe Iso8601TimeOption
    }

{-| Note that a "Year" may differ based on the representation.
For example, 2019-12-30 and 2020-W01-01 are the same date.

So while all members of this sum type share a Year, they're not
freely interchangeable.
-}
type Iso8601DateOption
    = YearMonthDay Int Int Int -- 1999-12-31
    | Year Int -- 1999
    | YearWeek Int Int -- 1999-W52
    | YearWeekDay Int Int Int -- 1999-W52-7
    | YearOrdinal Int Int -- 1999-354


type Iso8601TimeOption
    = Hour Int (Maybe Float) -- 09, 09.5
    | HourMinute Int Int (Maybe Float) -- 09:59, 09:59.5
    | HourMinuteSecond Int Int Int (Maybe Float) -- 09:59:59, 09:59:59.999