# TzWorld


Resolve timezones from a location using data from the

## Installation

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

def deps do
    {:tz_world, "~> 0.5.0"}

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}`.

### Configuration

There is no mandatory configuration required however two options may be
configured in `config.exs`:

config :tz_world,
  # The default is the `priv` directory of `:tz_world`
  data_dir: "geodata/directory",
  # The default is either the trust store included in the
  # libraries `CAStore` or `certifi` or the platform
  # trust store.
  cacertfile: "path/to/ca_trust_store"

## 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.

The recommended backend is `TzWorld.Backend.EtsWithIndexCache`.

For example:

defmodule MyApp.Application do
  @moduledoc false

  use Application

  def start(_type, _args) do
    children = [

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

* `TzWorld.Backend.Memory` which retains all data in memory for fast (but *not*
  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 (approximately 500ms in

* `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.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 required and to install or update it run:

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]( 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

## 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.

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}