# `DSMR.Timestamp`
[🔗](https://github.com/mijnverbruik/dsmr/blob/v1.1.0/lib/dsmr/timestamp.ex#L1)

A DSMR timestamp.

DSMR timestamps contain a naive date and time. Some telegrams also include a
daylight saving time marker: `"W"` for winter time or `"S"` for summer time.

# `t`

```elixir
@type t() :: %DSMR.Timestamp{dst: binary() | nil, value: NaiveDateTime.t()}
```

# `to_datetime`

```elixir
@spec to_datetime(t()) :: {:ok, DateTime.t()} | {:error, :missing_dst}
```

Converts a timestamp to a UTC `DateTime`.

DSMR timestamps are Dutch local time; the DST marker disambiguates the UTC
offset (`"W"` means UTC+1, `"S"` means UTC+2). The fixed offsets make this
conversion work without a timezone database dependency.

Returns `{:error, :missing_dst}` for timestamps without a DST marker
(found in DSMR 2.2/3.0 telegrams), as their UTC offset is ambiguous around
the DST transitions.

## Examples

    iex> DSMR.Timestamp.to_datetime(%DSMR.Timestamp{value: ~N[2017-01-02 19:20:02], dst: "W"})
    {:ok, ~U[2017-01-02 18:20:02Z]}

    iex> DSMR.Timestamp.to_datetime(%DSMR.Timestamp{value: ~N[2017-07-02 19:20:02], dst: "S"})
    {:ok, ~U[2017-07-02 17:20:02Z]}

    iex> DSMR.Timestamp.to_datetime(%DSMR.Timestamp{value: ~N[2017-01-02 19:20:02]})
    {:error, :missing_dst}

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*Consult [api-reference.md](api-reference.md) for complete listing*