给定 IANA 时区和本地时间，将其解析为 Maybe Posix？

Question

在 Elm 中有没有办法在不使用端口的情况下将本地时间（例如 string 2019-03-18T09:10:12.4；没有指定偏移量）和时区（例如Australia/Sydney）转换为可能的Posix值（即，该时间转换为 UTC）？

---

有waratuman/time-extra，但它似乎只适用于 Date 部分。遗憾的是rtfeldman/elm-iso8601-date-strings不使用timezones。

在 JS 中，有诸如moment-tz和date-fns-timezone之类的选项，但是避免 JS 互操作以进行频繁的日期解析会简单得多。

Answer 1

通过结合justinmimbs/time-extra和justinmimbs/timezone-data，您应该能够完全在 Elm 中获得有效的 posix 。

演示：https://ellie-app.com/54tyw9yvsQga1

首先，您需要将您的转换timestampWithoutTimezone为Parts：

toParts : String -> Maybe Parts
toParts timestampWithoutTimezone =
    timestampWithoutTimezone
        |> Regex.find regex
        |> List.map .submatches
        |> List.head
        |> Maybe.andThen Maybe.Extra.combine
        |> Maybe.andThen listToParts

regex : Regex
regex =
    Maybe.withDefault Regex.never <|
        Regex.fromString "^(\\d{4})-(\\d{2})-(\\d{2})T(\\d{2}):(\\d{2}):(\\d{2})\\.(\\d)$"


monthLookup : Dict String Month
monthLookup =
    Dict.fromList [ ( "01", Jan ), ( "02", Feb ), ( "03", Mar ), ( "04", Apr ), ( "05", May ), ( "06", Jun ), ( "07", Jul ), ( "08", Aug ), ( "09", Sep ), ( "10", Oct ), ( "11", Nov ), ( "12", Dec ) ]


listToParts : List String -> Maybe Parts
listToParts list =
    let
        toInt : Int -> Maybe Int
        toInt index =
            list |> List.Extra.getAt index |> Maybe.andThen String.toInt
    in
    Maybe.map2 Parts
        (toInt 0)
        (list |> List.Extra.getAt 1 |> Maybe.andThen (\month -> Dict.get month monthLookup))
        |> Maybe.andThen (\parts -> Maybe.map5 parts (toInt 2) (toInt 3) (toInt 4) (toInt 5) (toInt 6))

然后，使用partsToPosix适当的Zone你可以得到一个 posix 值：

toPosix : Time.Zone -> String -> Maybe Posix
toPosix zone timestampWithoutTimezone =
    timestampWithoutTimezone
        |> toParts
        |> Maybe.map (Time.Extra.partsToPosix zone)

库作者建议您将评估的区域值存储在模型中：

model = { zone = TimeZone.australia__sydney () }

toPosix model.zone "2019-03-18T09:10:12.4"