local new_timetable = require"luatz.timetable".new

--- Parse an RFC 3339 datetime at the given position
-- Returns a time table and the `tz_offset`
-- Return value is not normalised (this preserves a leap second)
-- If the timestamp is only partial (i.e. missing "Z" or time offset) then `tz_offset` will be nil
-- TODO: Validate components are within their boundarys (e.g. 1 <= month <= 12)
local function rfc_3339(str, init)
    local year, month, day, hour, min, sec, patt_end = str:match(
        "^(%d%d%d%d)%-(%d%d)%-(%d%d)[Tt](%d%d%.?%d*):(%d%d):(%d%d)()", init) -- luacheck: ignore 631
    if not year then
        return nil, "Invalid RFC 3339 timestamp"
    end
    year = tonumber(year, 10)
    month = tonumber(month, 10)
    day = tonumber(day, 10)
    hour = tonumber(hour, 10)
    min = tonumber(min, 10)
    sec = tonumber(sec, 10)

    local tt = new_timetable(year, month, day, hour, min, sec)

    local tz_offset
    if str:match("^[Zz]", patt_end) then
        tz_offset = 0
    else
        local hour_offset, min_offset = str:match("^([+-]%d%d):(%d%d)", patt_end)
        if hour_offset then
            tz_offset = tonumber(hour_offset, 10) * 3600 + tonumber(min_offset, 10) * 60
        else -- luacheck: ignore 542
            -- Invalid RFC 3339 timestamp offset (should be Z or (+/-)hour:min)
            -- tz_offset will be nil
        end
    end

    return tt, tz_offset
end

return {
    rfc_3339 = rfc_3339,
}
