Kalecto
=======

Glue between Kalends and Ecto.
For saving dates, times and datetimes in Ecto.

    defp deps do
      [  {:kalecto, ">= 0.0.1"},  ]
    end

The types are:

| Ecto type             | Primitive type             | Kalends type
| ----------------------|----------------------------|---------------------------|
| Kalecto.Date          | date                       | Kalends.Date              |
| Kalecto.Time          | time                       | Kalends.Time              |
| Kalecto.DateTimeUTC   | datetime                   | Kalends.DateTime          |
| Kalecto.NaiveDateTime | datetime                   | Kalends.NaiveDateTime     |

If you have a datetime as a primitive type, you can use NaiveDateTime or DateTimeUTC.
If you have a date as a primitive type, you can use Kalecto.Date.
If you have a time as a primitive type, you can use Kalecto.Time.

Microseconds of NaiveDateTime and DateTimeUTC are discarded/ignored if present.

## Example usage

In your Ecto schema:

    schema "weather" do
      field :city, :string
      field :nice_date, Kalecto.Date
      field :nice_time, Kalecto.Time
      field :nice_datetime, Kalecto.DateTimeUTC
      field :another_datetime, Kalecto.NaiveDateTime
      timestamps
    end

If you have a Kalends DateTime in the Etc/UTC timezone
you can save it in Ecto as a DateTimeUTC.

Let's create a new DateTime to represent "now":

    iex> example_to_be_saved_in_db = Kalends.DateTime.now_utc
    %Kalends.DateTime{abbr: "UTC", day: 2, hour: 16, microsec: 245828, min: 48,
     month: 3, sec: 19, std_off: 0, timezone: "Etc/UTC", utc_off: 0, year: 2015}

Another way of getting a DateTime is parsing JavaScript style milliseconds:

    iex> parsed_datetime = Kalends.DateTime.Parse.js_ms!("1425314899000")
    %Kalends.DateTime{abbr: "UTC", day: 2, hour: 16, microsec: 0, min: 48, month: 3,
     sec: 19, std_off: 0, timezone: "Etc/UTC", utc_off: 0, year: 2015}

Since the field nice_datetime is of the DateTimeUTC type, we can save
Kalends.DateTime structs there if they are in the Etc/UTC timezone:

    weather_struct_to_be_saved = %Weather{nice_datetime: parsed_datetime}

When a Kalecto.DateTimeUTC type is received from the database it is loaded as a
Kalends.DateTime struct. We can use the functions in Kalends to shift this UTC
datetime to another time zone:

    iex> example_loaded_from_db |> Kalends.DateTime.shift_zone!("Europe/Copenhagen")
    %Kalends.DateTime{abbr: "CET", day: 2, hour: 17, microsec: nil, min: 48,
      month: 3, sec: 19, std_off: 0, timezone: "Europe/Copenhagen", utc_off: 3600,
      year: 2015}

Or we could get the unix timestamp:

    iex> example_loaded_from_db |> Kalends.DateTime.Format.unix
    1425314899

Or format it via strftime:

    iex> example_loaded_from_db |> Kalends.DateTime.Format.strftime!("The time is %T and it is %A.")
    "The time is 16:48:19 and it is Monday."

More information about Kalends functionality in the Kalends documentation: http://hexdocs.pm/kalends/

## Roadmap

The next planned feature is being able to save DateTime structs that are not
UTC. Saved DateTimes should preserve the timezone, hour, minute etc. If a
timezone's rules/offset is changed the best case scenario is that the only
thing that changes when the DateTime is loaded from the db is the offset. That
way, if you avoid having the wall time change.