# TzWorld

Resolve timezones from a location using data from the [timezone-boundary-builder](https://github.com/evansiroky/timezone-boundary-builder) project.

## Installation

Add `tz_world` to your list of dependencies in `mix.exs`:

```elixir
def deps do
  [
    {:tz_world, "~> 0.4.0"}
  ]
end
```

After adding `TzWorld` as a dependency, run `mix deps.get` to install it. Then run `mix tz_world.update` to install the timezone data.

**NOTE** No data is installed with the package and until the data is installed with `mix tz_world.update` all calls to `TzWorld.timezone_at/1` will return `{:error, :time_zone_not_found}`.

## Backend selection

`TzWorld` provides alternative strategies for managing access to the backend data. Each backend is implemented as a `GenServer` that needs to be either manually started with `BackendModule.start_link/1` or preferably added to your application's supervision tree.

For example:
```elixir
defmodule MyApp.Application do
  @moduledoc false

  use Application

  def start(_type, _args) do
    children = [
      ...
      TzWorld.Backend.DetsWithIndexCache
    ]

    opts = [strategy: :one_for_one, name: MyApp.Supervisor]
    Supervisor.start_link(children, opts)
  end
end
```
The following backends are available:

* `TzWorld.Backend.Memory` which retains all data in memory for fastest performance at the expense of using approximately 1Gb of memory
* `TzWorld.Backend.Dets` which uses Erlang's `:dets` data store. This uses negligible memory at the expense of slow access times (approximaltey 500ms in testing)
* `TzWorld.Backend.DetsWithIndexCache` which balances memory usage and performance. This backend is recommended in most situations since its performance is similar to `TzWorld.Backend.Memory` (about 5% slower in testing) and uses about 25Mb of memory
* `TzWorld.Backend.Ets` which uses `:ets` for storage. With the default settings of `:compressed` for the `:ets` table its memory consumption is about 512Mb  but with access that is over 20 times slower than `TzWorld.Backend.DetsWithIndexCache`
* `TzWorld.Backend.EtsWithIndexCache` which uses `:ets` for storage with an additional in-memory cache of the bounding boxes. This still uses about 512Mb but is faster than any of the other backends by about 40%

## Installing the Timezones Geo JSON data

Installing `tz_world` from source or from hex does not include the timezones geo JSON data. The data is requried and to install or update it run:
```elixir
mix tz_world.update
```
This task will download, transform, zip and store the timezones geo data. Depending on internet and computer speed this may take a few minutes.

### Updating the Timezone data

From time-to-time the timezones geo JSON data is updated in the [upstream project](https://github.com/evansiroky/timezone-boundary-builder/releases). The mix task `mix tz_world.update` will update the data if it is available. This task can be run at any time, it will detect when new data is available and only download it when a new release is available.

A running application can also be instructed to reload the data by executing `TzWorld.reload_timezone_data`.

## Usage

The primary API is `TzWorld.timezone_at`. It takes either a `Geo.Point` struct or a `longitude` and `latitude` in degrees. Note the parameter order: `longitude`, `latitude`. It also takes and optional second parameter, `backend`, which must be one of the configured and running backend modules.  By default `timezone_at/2` will detect a running backend and will raise an exception if no running backend is found.

```elixir
iex> TzWorld.timezone_at(%Geo.Point{coordinates: {3.2, 45.32}})
{:ok, "Europe/Paris"}

iex> TzWorld.timezone_at({3.2, 45.32})
{:ok, "Europe/Paris"}

iex> TzWorld.timezone_at(%Geo.PointZ{coordinates: {-74.006, 40.7128, 0.0}})
{:ok, "America/New_York"}

iex> TzWorld.timezone_at(%Geo.Point{coordinates: {1.3, 65.62}})
{:error, :time_zone_not_found}
```