# RabbitCarrots

RabbitCarrots is a simple background worker to handle the consumption of RabbitMQ message in Rails applications. It is an opinionated library that solves the consumption of messages among  microservices, given the following conditions:

1. RabbitMQ is used as an event bus for communication.
2. Messages are routed using a single exchange, multiple routing keys.
3. One routing key or more can be bound to a single queue. 
4. The app is a built with Ruby on Rails.

### Considerations

The gem adds a rake task to the project using the Railtie framework of Rails. Therefore, the task should be run as a separate process that is independent from the application server.

## Installation

Install the gem and add to the application's Gemfile by executing:

    $ bundle add rabbit_carrots

If bundler is not being used to manage dependencies, install the gem by executing:

    $ gem install rabbit_carrots

## Usage

Add the following to ```config/initializers/rabbit_carrots.rb```:

```ruby
RabbitCarrots.configure do |c|
  c.rabbitmq_host = ENV.fetch('RABBITMQ__HOST', nil)
  c.rabbitmq_port = ENV.fetch('RABBITMQ__PORT', nil)
  c.rabbitmq_user = ENV.fetch('RABBITMQ__USER', nil)
  c.rabbitmq_password = ENV.fetch('RABBITMQ__PASSWORD', nil)
  c.rabbitmq_vhost = ENV.fetch('RABBITMQ__VHOST', nil)
  c.rabbitmq_exchange_name = ENV.fetch('RABBITMQ__EXCHANGE_NAME', nil)
  c.automatically_recover = true
  c.network_recovery_interval = 5
  c.recovery_attempts = 5
  c.orm = :activerecord || :mongoid
  c.routing_key_mappings =  [
    { routing_keys: ['RK1', 'RK2'], queue: 'QUEUE_NAME', handler: 'CLASS HANDLER IN STRING' },
    { routing_keys: ['RK1', 'RK2'], queue: 'QUEUE_NAME', handler: 'CLASS HANDLER IN STRING' }
  ]
end

```

Note that handler is a class that must implement a method named ```handle!``` that takes 4 parameters as follow: 

```ruby
class DummyEventHandler
   def self.handle!(channel, delivery_info, properties, payload)
      # Handle the received message from the queue 
   end
end
```

Inside the handle message, you can NACK the message without re-queuing by raising ```RabbitCarrots::EventHandlers::Errors::NackMessage``` exception.

To NACK and re-queue, raise ```RabbitCarrots::EventHandlers::Errors::NackAndRequeueMessage``` exception. 

If no errors are thrown, the message will be acknowledged soon after the ```handle!``` method returns. 

Note: Any other unrescued exception raised inside ```handle!``` the that is a subclass of ```StandardError``` will trigger a NACK and re-queue.

### Running

For better scalability and improved performance, you can run rabbit_carrots in standalone mode by invoking the following command:
```bundle exec rake rabbit_carrots:eat```.

#### Puma

For small and medium sized projects, you can delegate the management of the rabbit_carrots to the Puma web server. To achieve that, add the following line to your puma.rb

```plugin :rabbit_carrots```

This will make sure that Puma will manage rabbit carrots as a background service and will gracefully terminate if rabbit_carrots eventually loses connection after multiple automatic recovery. 
## Development

After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and the created tag, and push the `.gem` file to [rubygems.org](https://rubygems.org).

## Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ditkrg/rabbit_carrots. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [code of conduct](https://github.com/[USERNAME]/rabbit_carrots/blob/master/CODE_OF_CONDUCT.md).

## License

The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).

## Code of Conduct

Everyone interacting in the RabbitCarrots project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the [code of conduct](https://github.com/[USERNAME]/rabbit_carrots/blob/master/CODE_OF_CONDUCT.md).