# TzWorld
[](https://hex.pm/packages/tz_world)
[](https://hex.pm/packages/tz_world)
[](https://hex.pm/packages/tz_world)
[](https://github.com/kimlai/tz_world)
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, "~> 0.5.0"}
]
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}`.
### Configuration
There is no mandatory configuration required however two options may be
configured in `config.exs`:
```elixir
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:
```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 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
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 required 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}
```
