# Galena
[](https://travis-ci.org/mendrugory/galena)
Galena is a topic consumer-producer library built on top of [GenStage](https://github.com/elixir-lang/gen_stage) for [Elixir](http://elixir-lang.org/).
I highly recommend to initiate your producers/consumers under a [Supervisor](http://elixir-lang.org/docs/stable/elixir/Supervisor).
## Installation
If [available in Hex](https://hex.pm/docs/publish), the package can be installed as:
* Add `galena` to your list of dependencies in `mix.exs`:
```elixir
def deps do
[{:galena, git: "https://github.com/mendrugory/galena.git"}] # or [{:galena, "~> 0.1.0"}] when is available
end
```
## Definition
* Define your Producer(s). Your producer could be connected to external system like RabbitMQ, Kafka, DataBases, ...
Code the function handle_produce(data), where data can be whatever, and
has to return a tuple where the first value has to be a topic and the second one the message.
To guarantee a good perfomance, try to optimize as much as possible this function.
```elixir
defmodule MyProducer do
use Galena.Producer
def handle_produce({topic, data}) do
{topic, data}
end
end
```
* Define your Producer-Consumer(s). A Producer-Consumer will have the functionalities of
a consumer and a producer. It needs an implementation close to a producer (handle_produce(topic, data))
and the initialization of a consumer.
```elixir
defmodule MyProducerConsumer do
use Galena.ProducerConsumer
def handle_produce(topic, data) do
result_topic = topic <> Integer.to_string(:rand.uniform(2))
{result_topic, "modified by producer-consumer: " <> data}
end
end
```
* Define and run your Consumer. Code the function handle_consume(topic, message).
A consumer could be subscribed to different topics of the
same producer or even to different producers. We have to indicate it using a Keyword list as first
parameter which has to contain the information about the producers.
```elixir
# Example
args = [
producers_info: [
{["topic_1", "topic_2", "topic_3"], :producer1},
{["topic_A"], :producer2},
{["topic_a", "topic_b"], :producer3},
{[], :producer4}
]
]
```
```elixir
defmodule MyConsumer do
use Galena.Consumer
def handle_consume(topic, message) do
IO.puts(topic <> ": " <> message)
end
end
```
## Running
* Run and begin to ingest data
```elixir
# One producer
iex> MyProducer.start_link([], [name: :producer])
# One producer-consumer
iex> MyProducerConsumer.start_link([producers_info: [{["topic"], :producer}]], [name: :prod_cons])
# Two consumers
iex> MyConsumer.start_link([producers_info: [{["topic1"], :prod_cons}]], [name: :consumer1])
iex> MyConsumer.start_link([producers_info: [{["topic2"], :prod_cons}]], [name: :consumer2])
# Data ingestion
iex> for i <- 1..100 do, MyProducer.ingest(:producer, {"topic", "Hola" <> Integer.to_string(:rand.uniform(100))})
```
## Test
* Run the tests.
```bash
mix test
```
