Implement server-side rendering of datatables in users#index

app/datatables/users_datatable.rb

@@ -0,0 +1,53 @@
+class UsersDatatable
+  delegate :params, :link_to, :current_ability, :show_roles, to: :@view
+
+  def initialize(view)
+    @view = view
+  end
+
+  def as_json(_options = {})
+    {
+      sEcho: params[:sEcho].to_i,
+      iTotalRecords: User.count,
+      iTotalDisplayRecords: users.count,
+      aaData: data
+    }
+  end
+
+  private
+
+  def data
+    paginate(users).map do |user|
+      [
+        user.id,
+        (user.confirmed? ? 'confirmed' : 'unconfirmed'),
+        user.email,
+        user.name,
+        user.registrations.where(attended: true).count,
+        (user.roles.empty? ? 'None' : "#{show_roles(user.get_roles.first(2))} #{'...' if user.get_roles.count > 2}"),
+        (link_to('View', Rails.application.routes.url_helpers.admin_user_path(user), class: 'btn btn-success') if current_ability.can?(:show, user)),
+        (link_to('Edit', Rails.application.routes.url_helpers.edit_admin_user_path(user), class: 'btn btn-primary') if current_ability.can?(:update, user))
+      ]
+    end
+  end
+
+  def users
+    @users ||= fetch_users
+  end
+
+  def fetch_users
+    sort_direction = params[:sSortDir_0] == 'desc' ? 'desc' : 'asc'
+    sort_column = %w(id state email name)[params[:iSortCol_0].to_i]
+    users = User.order("#{sort_column} #{sort_direction}")
+    if params[:sSearch].present?
+      users = users.where('name like :search or email like :search', search: "%#{params[:sSearch]}%")
+    end
+    users
+  end
+
+  def paginate(users)
+    per_page = params[:iDisplayLength].to_i > 0 ? params[:iDisplayLength].to_i : 10
+    page = params[:iDisplayStart].to_i / per_page + 1
+    users.offset((page - 1) * per_page).limit(per_page)
+  end
+end