### Slack notifier

This notifier sends notifications to a slack channel using the slack-notifier gem.

#### Usage

Just add the [slack-notifier](https://github.com/stevenosloan/slack-notifier) gem to your `Gemfile`:

```ruby
gem 'slack-notifier'
```

To configure it, you need to set at least the 'webhook_url' option, like this:

```ruby
Rails.application.config.middleware.use ExceptionNotification::Rack,
                                        email: {
                                          email_prefix: '[PREFIX] ',
                                          sender_address: %{"notifier" <notifier@example.com>},
                                          exception_recipients: %w{exceptions@example.com}
                                        },
                                        slack: {
                                          webhook_url: '[Your webhook url]',
                                          channel: '#exceptions',
                                          additional_parameters: {
                                            icon_url: 'http://image.jpg',
                                            mrkdwn: true
                                          }
                                        }
```

The slack notification will include any data saved under `env['exception_notifier.exception_data']`.

An example of how to send the server name to Slack in Rails (put this code in application_controller.rb):

```ruby
before_action :set_notification

def set_notification
  request.env['exception_notifier.exception_data'] = { 'server' => request.env['SERVER_NAME'] }
  # can be any key-value pairs
end
```

If you find this too verbose, you can determine to exclude certain information by doing the following:

```ruby
Rails.application.config.middleware.use ExceptionNotification::Rack,
                                        slack: {
                                          webhook_url: '[Your webhook url]',
                                          channel: '#exceptions',
                                          additional_parameters: {
                                            icon_url: 'http://image.jpg',
                                            mrkdwn: true
                                          },
                                          ignore_data_if: lambda {|key, value|
                                            "#{key}" == 'key_to_ignore' || value.is_a?(ClassToBeIgnored)
                                          }
                                        }
```

Any evaluation to `true` will cause the key / value pair not be be sent along to Slack.


the `slack-notifier` gem allows to override the channel default value, if you ever
need to send a notification to a different slack channel. Simply add the
`channel` option when calling `.notify_exception`

```ruby
ExceptionNotifier.notify_exception(
  exception,
  env: request.env,
  channel: '#my-custom-channel', # Make sure the channel name starts with `#`
  data: {
    error: error_variable,
    server: server_name
  }
)
```

If you ever need to add more `slack-notifier` specific options, and
particularly to the `#ping` method of the slack notifier, you can use
the `pre_callback` option when defining the middleware.
```ruby
 pre_callback: proc { |opts, _notifier, _backtrace, _message, message_opts|
   message_opts[:channel] = opts[:channel] if opts.key?(:channel)
 }

```
- `message_opts` is the hash you want to append to if you need to add an option.
- `options` is the hash containing the values when you call
  `ExceptionNotification.notify_exception`

An example implementation would be:
```ruby
config.middleware.use ExceptionNotification::Rack,
  slack: {
    webhook_url: '[Your webhook url]',
    pre_callback: proc { |opts, _notifier, _backtrace, _message, message_opts|
      message_opts[:ping_option] = opts[:ping_option] if
      opts.key?(:ping_option)
    }
  },
  error_grouping: true
```
Then when calling from within your application code:
```ruby
ExceptionNotifier.notify_exception(
  exception,
  env: request.env,
  ping_option: 'value',
  # this will be passed to the slack notifier's `#ping`
  # method, as a parameter. The `:pre_callback` hook will catch it
  # and do that for you.
  # Helpful, if the API evolves, you only need to update
  # the `slack-notifier` gem
  data: {
    error: error_variable,
    server: server_name
  }
)

```
#### Options

##### webhook_url

*String, required*

The Incoming WebHook URL on slack.

##### channel

*String, optional*

Message will appear in this channel. Defaults to the channel you set as such on slack.

##### username

*String, optional*

Username of the bot. Defaults to the name you set as such on slack

##### custom_hook

*String, optional*

Custom hook name. See [slack-notifier](https://github.com/stevenosloan/slack-notifier#custom-hook-name) for
more information. Default: 'incoming-webhook'

##### additional_parameters

*Hash of strings, optional*

Contains additional payload for a message (e.g avatar, attachments, etc). See [slack-notifier](https://github.com/stevenosloan/slack-notifier#additional-parameters) for more information.. Default: '{}'

##### additional_fields

*Array of Hashes, optional*

Contains additional fields that will be added to the attachement. See [Slack documentation](https://api.slack.com/docs/message-attachments).