module Gigasecond exposing (add)

import Date
import Time
import String


add : String -> Result String String
add x =
    x
        |> Date.fromString
        |> Result.map (add' gigasecond)
        |> Result.map format


add' : Time.Time -> Date.Date -> Date.Date
add' t d =
    d
        |> Date.toTime
        |> flip (+) t
        |> Date.fromTime


gigasecond : Time.Time
gigasecond =
    10 ^ 12


format : Date.Date -> String
format date =
    let
        date =
            toGMT date
    in
        --toString date
        [ Date.year date
            |> toString
        , "-"
        , Date.month date
            |> monthToInt
            |> Maybe.withDefault 1
            |> toString
            |> String.pad 2 '0'
        , "-"
        , Date.day date
            |> toString
            |> String.pad 2 '0'
        , "T"
        , Date.hour date
            |> toString
            |> String.pad 2 '0'
        , ":"
        , Date.minute date
            |> toString
            |> String.pad 2 '0'
        , ":"
        , Date.second date
            |> toString
            |> String.pad 2 '0'
        ]
            |> String.concat


monthToInt : Date.Month -> Maybe Int
monthToInt n =
    case n of
        Date.Jan ->
            Just 1

        Date.Feb ->
            Just 2

        Date.Mar ->
            Just 3

        Date.Apr ->
            Just 4

        Date.May ->
            Just 5

        Date.Jun ->
            Just 6

        Date.Jul ->
            Just 7

        Date.Aug ->
            Just 8

        Date.Sep ->
            Just 9

        Date.Oct ->
            Just 10

        Date.Nov ->
            Just 11

        Date.Dec ->
            Just 12


toGMT : Date.Date -> Date.Date
toGMT date =
    let
        tzOffset =
            date
                |> toString
                |> String.split " "
                |> List.drop 5
                |> List.head
                |> Maybe.withDefault "GMT-0000"
                |> String.dropLeft 3
                |> String.toInt
                |> Result.withDefault 0
                |> flip (//) 100
                |> toFloat
                |> (*) -Time.hour
    in
        add' tzOffset date