rails implementation transactional emailing with queueing

plos_transactional_email.rb

# app/controllers/events_controller.rb
class EventsController < ApplicationController
  def create
    Event.create(params.permit(:event_type, :doi, :event_data))
    render json: {}, status: :ok
  end
end

# app/models/event.rb
class Event < ActiveRecord
  # not sure if this is the best place for this mapping
  # could beling in DB
  EVENT_QUEUE_TIME_MAP = {
    'event_1' => 0,
    'event_2' => 24
  }
  
  after_create :perform_email_job, if: :enqueue_job?
  
  def perform_email_job
    EmailEventJob.set(wait: queue_time.hours).perform_later(id, doi, event_type, queue_time.zero?)
    # do we care to handle unlisted events?
  end
  
  def queue_time
    EVENT_QUEUE_TIME_MAP[event_type]
  end
  
  def enqueue_job?
    # there might be some sort of db locking we'd need to implement
    # to prevent some sort of race condition?
    queue_time.zero? || Event.where(doi: doi, event_type: event_type).count == 1
  end
end

# app/jobs/email_event_job.rb
class EmailEventJob < ActiveJob
  def perform(event_id, doi, event_type, use_id)
    where_args = use_id ? { id: event_id } : { doi: doi, event_type: event_type }
    events = Event.where(where_args) # maybe add some sort of DB lock
    return if events.empty? # this might happen? Ideally not.
    recepients = get_author_emails(doi)
    # only email client specific api call, can be swapped out
    SendgridClient.send_email(event_type, recepients, events.pluck(:event_data)) # should raise error if fails
    events.destroy_all # we can soft delete if we want to keep a record
  end
  
  def get_author_emails(doi)
    # TODO: this needs to get figured out and probably cached
  end
end

# lib/sendgrid_client.rb
require 'sendgrid-ruby'
require 'json'
include SendGrid

class SendgridClient
  EVENT_TEMPLATE_MAP = {
    'event_1' => 'abc123',
    'event_2' => 'def456'
  }
  class << self
    def send_email(event_type, recepients, event_data)
      mail = Mail.new
      mail.template_id = EVENT_TEMPLATE_MAP[event_type]
      mail.from = Email.new(email: 'no-reply@plos.org')
      personalization = Personalization.new
      recepients.each do |recepient|
        personalization.add_to(Email.new(email: recepient))
      end
      # we kinda assume the first set of data coming in is pretty much
      # tailored for emailing, but we could also massage it here too.
      personalization.add_dynamic_template_data(events: event_data)
      mail.add_personalization(personalization)
      sg = SendGrid::API.new(api_key: ENV['SENDGRID_API_KEY'], host: 'https://api.sendgrid.com')
      sg.client.mail._('send').post(request_body: mail.to_json)
    end
  end
end