Adds logic to send proposal notifications in batches

WIP batches tests

app/controllers/admin/system_emails_controller.rb

@@ -24,6 +24,19 @@ class Admin::SystemEmailsController < Admin::BaseController
     end
   end
 
+  def moderate_pending
+    ProposalNotification.find(params[:id]).moderate_system_email(current_user)
+
+    redirect_to admin_system_email_preview_pending_path("proposal_notification_digest")
+  end
+
+  def send_pending
+    Notification.send_pending
+
+    flash[:notice] = t("admin.system_emails.preview_pending.send_pending_notification")
+    redirect_to admin_system_emails_path
+  end
+
   private
 
   def load_system_email

app/models/notification.rb

@@ -68,4 +68,29 @@ class Notification < ActiveRecord::Base
     end
   end
 
+  def self.send_pending
+    run_at = first_batch_run_at
+    User.email_digest.find_in_batches(batch_size: batch_size) do |users|
+      users.each do |user|
+        email_digest = EmailDigest.new(user)
+        email_digest.deliver(run_at)
+      end
+      run_at += batch_interval
+    end
+  end
+
+  private
+
+  def self.batch_size
+    10000
+  end
+
+  def self.batch_interval
+    20.minutes
+  end
+
+  def self.first_batch_run_at
+    Time.current
+  end
+
 end