Noticent

Noticent is a Ruby gem for user notification management. It is written to deliver a developer friendly way to managing application notifications in a typical web application. Many applications have user notification: sending emails when a task is done or support for webhooks or Slack upon certain events. Noticent makes it easy to write maintainable code for notification subscription and delivery in a typical web application.

The primary design goal for Noticent is developer friendliness. Using Noticent, you should be able to:

• Create new notification types
• Tell the current state of notifications, subscriptions and distribution channels.
• Support multiple notification channels like email, chat applications, mobile push, webhooks and more.
• Test your notifications

Installation

Add this line to your application's Gemfile:

gem 'noticent'

And then execute:

bundle

Or install it yourself as:

gem install noticent

Run Generators

rails g noticent:install

Now run the migrations

rake db:migrate

Usage

Noticent is written to be used in a Rails application but you should be able to use it in other Ruby / Rack based applications if you need to.

Basics

Noticent uses the following concepts:

Alert

Alert is a type of notification. For example, a new user signing up could be defined as an Alert.

Scope

Scope is like a namespace for Alerts. In many applications, you will only have 1 Scope. However, sometimes you might have different types of Alerts for different parts of your application. For example, "new blog post written" and "blog post updated" Alerts could be associated with the a "blog" Scope, while a "new comment added" Alert is associated with another Scope. Using Scope is useful when you have many different groups of Alerts in your application.

Channel

Channel is a distribution channel for your Alerts. Examples of Channels are Email, Slack, Webhook, Mobile or browser notification.

Recipient

Recipient is a person or system that receives Alerts. This could be a user for Channels like Email or a system for a Webhook Channel.

Payload

Payload is a data structure (class) that carries everything you'd need to send an Alert to a Recipient over a Channel.

Product

A product acts as a filter on alerts. For example, you might want to list different set of alerts for different parts of your application. To achieve that you can define each part as a product and use applies.to and applies.not_to to say how an alert applies to each part of the application. Products don't have an effect on how alerts are run, but they can be used to list which alerts apply to each part of an application using Noticent.configuration.product_by_alert method.

If an alert doesn't have an applies, it will be applicable to none of the products defined.

Integration

Noticent tries to make very few assumptions about your application, like what you call your Recipients or what your Scopes are. However it also enforces some opinions to make the whole system easier to use and maintain.

Configuration

The most important part of using Noticent is the configuration part where you define scopes, channels and your alerts. Once configured, you can hook it up to the rest of your code. This example assumes integration in a Rails application.

If you have run the generators, you should now have a file called config/initializers/noticent.rb. You can edit it as you like:

Noticent.configure do
    channel :email

    scope :account do
        alert(:new_signup){ notify :owner}
        alert(:new_team_member) { notify :users }
    end
end

Now you'd need to tell Noticent how to send emails by creating an email channel. This can be done in app/models/noticent/channels/email.rb:

class Email < ::Noticent::Channel
    def new_signup
        # send email here
    end

    def new_team_member
        # send email here
    end
end

Now that we have our channel, we can define a Payload. We can do this in app/modesl/noticent/account_payload.rb:

class AccountPayload
    attr_reader :account
    attr_reader :current_user

    def initializer(account_id, current_user)
        @account = Account.find account_id
    end

    def users
        @account.users
    end

    def owner
        @account.owner
    end
end

You can now create your email templates in app/models/noticent/views/email with 2 files called new_signup.html.erb and new_team_member.html.erb the same way you would write email templates for Rails mailers:

Hello <%= @owner.name %>!
A new user just signed up.

and

You now have a new team member. Make sure to say hi!

Until now, this is very much like Rail's own mailers and follows the same principles: Payload is like a model, Channel is the equivalent of a controller and the html view file is the view.

This first difference here is that you can use "front matter" in your views. This is useful when you need more than just text or HTML in your notifications. For an email channel, the front matter can hold a template for the email subject for example:

subject: New member for <%= @team.name %>
---
Hello!

You now have a new team member who signed up as an admin for <%= @team.name %>

In the channel, you can use this:

class EmailChannel < ::Noticent::Channel

    def new_member
        data, content = render
        send_email(subject: data[:subject], content: content) # this is an example code
    end
end

The render method looks for the right file under the views directory and loads and renders the ERB file while returning any front matter if available.

Use of front matter becomes more important in channels that have a more complex API like Slack (message color can be stored in the front matter) for example.

Now let's go back to our configuration file and see what else we can do. Here is an example of a Noticent configuration file in full:

Noticent.configure do
    hooks :pre_channel_registration, my_hooks
    hooks :post_alert_registration, my_hooks

    channel :email
    channel :slack
    channel :webhook, klass: MyWebhookChannel
    channel :dashboard, group: :internal
    
    product :product_foo
    product :product_buzz
    product :product_bar

    scope :account, check_constructor: false do
        alert :new_user do
            applies.to :product_foo
            notify :users
            notify(:staff).on(:internal)
            notify :owners
            
            default true             
        end
    end

    scope :comment do
        alert :new_comment, constructor_name: :some_constructor do
            applies.not_to :product_buzz
            notify :commenter
            notify :author
            
            default true  
            default(false) { on(:email) }            
        end
        alert :comment_updated do
            notify :commenter
        end
    end

    scope :staff_comment, payload_class: AnotherPayloadClass do
        alert :marked_as_answer do
            notify(:staff).on(:internal)
        end
    end
end

Sending Alerts

To send an Alert, call the notify method:

account_payload = AccountPayload.new(1, user.first)
Noticent.notify(:new_user, account_payload)

While it is possible to define and use alert names as symbols, Noticent also creates a constant with the name of the alert under the Noticent namespace to help with the use of alert names. By using the constants you can make sure alert names are free of typos.

For example, if you have an alert called some_event then after configuration there will be a constant called Noticent::ALERT_SOME_EVENT available to use with the value :some_event.

Using Each Noticent Component

Payload

To understand how to use Noticent, it's important to know the conventions it uses. First, payloads: A payload is a class and should have methods named after each one of the recipient groups specified in the configuration. For example, if an alert should be sent to users then payload should have a method or attribute called users. This method is called at the point the notifications need to be sent to retrieve the recipients. It is up to you what each recipient is: it could be an email address (string) or the entire user object or an ID. Your channel class will be given this and should know how to handle it.

It is recommended to explicitly define the class type of each scope. This ensures integrity of the alerts in runtime:

Noticent.configure do
    scope :account, payload_class: SomeOtherClass do
        #...
    end
end

If specified, the type of the payload is checked against this class at runtime (when Notify is called).

To enforce development type consistency payload should have class method constructors that are named after the alert names. This can be turned off by setting check_constructor on scopes to false. To share the same class method constructor for different alerts, you can use the constructor_name on alert to tell Noticent to look for a constructor that is not named after the alert itself. This is a validation step only and doesn't affect the performance of Noticent.

Channel

Channels should be derived from ::Noticent::Channel class and called the same as with the name of the channel with a Channel suffix: email would be EmailChannel and slack will be SlackChannel. Also, channels should have a method for each type of alert they are supposed to handle. Channel class can be changed using the klass argument during definition.

Channels can also have groups. If no group is supplied, a channel will belong to the default group. Groups can be used to send alerts to a subset of channels:

Noticent.configure do
    channel :email
    channel :private_emails, group: :internal
    channel :slack
    channel(:team_slack, klass: Slack, group: :internal) do
      using(fuzz: :buzz) 
    end 

    alert :some_event do
        notify :users
        notify(:staff).on(:internal)
    end
end

In the example above, we are creating 2 flavors of the slack channel, one called team_slack but using the same class and configured differently. When using is used in a channel, any attribute passed into using will be called on the channel after creation with the given values. For example, in this example, the Slack class is instantiated and attribute fuzz is set to :buzz on it before the alert method is called.

You can use on with a channel name instead of a channel group name instead:

Noticent.configure do
    channel :email
    channel :private_emails, group: :internal
    channel :slack

    alert :some_event do
        notify(:users).on(:internal) # this is a group name
        notify(:staff).on(:slack)    # this is a channel name
    end
end

You can use render in the channel code to render and return the view file and its front matter (if available). By default, channel will look for html and erb as the file content and format. You can change these both when calling render or at the top of the controller:

class SlackChannel < ::Noticent::Channel
    default_format :json
    default_ext :erb
end

or

data, content = render(format: :erb, ext: :json)

You can also use a different layout for each render:

data, content = render layout: 'my_layout'

By default, no layout is used.

Views

Views are like Rails views. Noticent supports rendering ERB files. You can also use layouts just like Rails. A layout is like a shared template layout.html.erb:

This is at the top

<%= @content %>

This is at the bottom

some_event.html.erb:

foo: bar
buzz: fuzz
---
This will be in the middle

Views can be of any type, like HTML or JSON which can be useful with API based channels.

Opt-ins

Noticent uses a combination of channel, alert and scope to determine if a recipient has subscribed to receive an alert or not. By default it uses the ActiveRecordOptInProvider class which uses a single database table for the process. You can write your own Opt-in provider if you want to store subscription (opt-in) state in a different place. See ActiveRecordOptInProvider for what such provider requires to operate.

Use Noticent.configuration.opt_in_provider's opt_in, opt_out and opted_in? methods to change the opt-in state of each recipient.

Default Values

You can specify a default opt-in value for each alert. By default alerts have a default value of false (no opt-in) unless this is globally changed (see Customization section).

The default value for an alert can be set while this can also be changed per channel. For example:

Noticent.configure do
  channel :email 
  channel :slack
  channel :webhook
  
  scope :post do 
    alert :foo do 
      notify :users 
      default(true) # sets the default value for all channels for this alert to true 
      default(false) { on(:slack) } # sets the default value for this alert to false for the slack channel only
    end
  end
end

Migration

Noticent provides a method to add new alerts or remove deprecated alerts from the existing recipients. To add a new alert type, you can use ActiveRecordOptInProvider.add_alert method:

Noticent.opt_in_provider.add_alert(scope: :foo, alert_name: :some_new_alert, recipient_ids: [1, 2, 3, 5, 6], channel: :email)

This will opt-in recipients with the given IDs for the new alert on the email channel.

To remove any deprecated alert, use the ActiveRecordOptInProvider.remove_alert method:

Noticent.opt_in_provider.remove_alert(scope: :foo, alert_name: :some_old_alert)

This removes all instances of the old alert from the opt-ins.

New Recipient Sign up

When a new recipient signs up, you might want to make sure they have all the default alerts setup for them. You can achieve this by calling Noticent.setup_recipient:

Noticent.setup_recipient(recipient_id: 1, scope: :post, entity_ids: [2])

This will adds the default opt-ins for recipient 1 on all channels that are applicable to it on scope post for entity 2.

Validation

Every time Noticent starts, it runs some validations on the configuration, classes that are defined, channels and alerts to make sure they are defined correctly and the supporting classes are in compliance with the requirements.

Testing Your Alerts

TO BE WRITTEN

Hooks

Hooks are extension points for Noticent. You can register them in your configuration:

Noticent.configure do
    hooks.add(:pre_channel_registration, custom_hook)
end

The valid hook points are pre_channel_registration, post_channel_registration, pre_alert_registration and post_alert_registration. Once the hook point is reached, the given object is called on the same method name as with the hook name.

Customization

The following items can be customized:

base_dir: Base directory for all Noticent assets.

base_module_name: Base module name for all Noticent assets.

opt_in_provider: Opt-in provider class. Default is ActiveRecordOptInProvider.

logger: Logger class. Default is stdout

halt_on_error: Should notification fail after the first incident of an error during rendering. Default is false

default_value: Default value for all alerts unless explicitly specified. Default is false

use_sub_modules: If set to true, Noticent will look for Channel and Scope classes in sub modules under the base_module_name. With use_sub_modules set to false, a channel named :email should be called Noticent::Email (if base_module_name is Noticent), while with use_sub_modules set to true, the same class should be Noticent::Channels::Email. For Payloads, the sub module name will be Payloads.

Development

After checking out the repo, run bin/setup to install dependencies. 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 tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/khash/noticent.