Enable org queues to use task pagination API (#11213)

Connects #11054. Enables back-end pagination for certain organizations (VSOs, VLJ support staff, hearing management branch) when the current user has the `use_task_pages_api` feature toggle on. Still needs some cosmetic love, but it's far enough along that I'd like some feedback on how this approach can be improved.

![caching-pagination](https://user-images.githubusercontent.com/32683958/60212556-8a23d600-982f-11e9-8dda-dca70423f50f.gif)

app/controllers/organizations/tasks_controller.rb

@@ -17,6 +17,8 @@ def index
   private
 
   def tasks
+    return [] if queue_config[:use_task_pages_api]
+
     Rails.logger.debug("starting GenericQueue tasks")
 
     # Temporarily limit hearings-management tasks to AOD tasks, because currently no tasks are loading

app/models/organization.rb

@@ -24,6 +24,10 @@ def show_regional_office_in_queue?
     false
   end
 
+  def use_task_pages_api?
+    false
+  end
+
   def non_admins
     organizations_users.includes(:user).non_admin.map(&:user)
   end

app/models/organizations/colocated.rb

@@ -8,4 +8,8 @@ def self.singleton
   def next_assignee(options = {})
     ColocatedTaskDistributor.new.next_assignee(options)
   end
+
+  def use_task_pages_api?
+    true
+  end
 end

app/models/organizations/hearings_management.rb

@@ -1,6 +1,10 @@
 # frozen_string_literal: true
 
 class HearingsManagement < Organization
+  def self.singleton
+    HearingsManagement.first || HearingsManagement.create(name: "Hearings Management", url: "hearings-management")
+  end
+
   def can_bulk_assign_tasks?
     true
   end
@@ -9,7 +13,7 @@ def show_regional_office_in_queue?
     true
   end
 
-  def self.singleton
-    HearingsManagement.first || HearingsManagement.create(name: "Hearings Management", url: "hearings-management")
+  def use_task_pages_api?
+    true
   end
 end

app/models/organizations/vso.rb

@@ -1,3 +1,7 @@
 # frozen_string_literal: true
 
-class Vso < Representative; end
+class Vso < Representative
+  def use_task_pages_api?
+    true
+  end
+end

app/models/queue_config.rb

@@ -17,17 +17,21 @@ def initialize(args)
   end
 
   def to_hash_for_user(user)
-    serialized_tabs = tabs.each { |tab| tab[:tasks] = serialized_tasks_for_user(tab[:tasks], user) }
-
     {
       table_title: format(COPY::ORGANIZATION_QUEUE_TABLE_TITLE, organization.name),
       active_tab: Constants.QUEUE_CONFIG.UNASSIGNED_TASKS_TAB_NAME,
-      tabs: serialized_tabs
+      tasks_per_page: TaskPager::TASKS_PER_PAGE,
+      use_task_pages_api: use_task_pages_api?,
+      tabs: tabs.map { |tab| attach_tasks_to_tab(tab, user) }
     }
   end
 
   private
 
+  def use_task_pages_api?
+    FeatureToggle.enabled?(:use_task_pages_api) && organization.use_task_pages_api?
+  end
+
   def tabs
     [
       include_tracking_tasks_tab? ? tracking_tasks_tab : nil,
@@ -37,8 +41,23 @@ def tabs
     ].compact
   end
 
+  def attach_tasks_to_tab(tab, user)
+    task_pager = TaskPager.new(assignee: organization, tab_name: tab[:name])
+
+    # Only return tasks in the configuration if we are using it to populate the first page of results.
+    # Otherwise avoid the overhead of the additional database requests.
+    tasks = use_task_pages_api? ? serialized_tasks_for_user(task_pager.paged_tasks, user) : []
+
+    tab.merge(
+      label: format(tab[:label], task_pager.total_task_count),
+      tasks: tasks,
+      task_page_count: task_pager.task_page_count,
+      total_task_count: task_pager.total_task_count,
+      task_page_endpoint_base_path: "#{organization.path}/task_pages?tab=#{tab[:name]}"
+    )
+  end
+
   def serialized_tasks_for_user(tasks, user)
-    return [] unless FeatureToggle.enabled?(:use_task_pages_api)
     return [] if tasks.empty?
 
     primed_tasks = AppealRepository.eager_load_legacy_appeals_for_tasks(tasks)
@@ -55,33 +74,24 @@ def include_tracking_tasks_tab?
   end
 
   def tracking_tasks_tab
-    name = Constants.QUEUE_CONFIG.TRACKING_TASKS_TAB_NAME
-    tasks = TaskPager.new(assignee: organization, tab_name: name).tasks_for_tab
-
     {
       label: COPY::ALL_CASES_QUEUE_TABLE_TAB_TITLE,
-      name: name,
+      name: Constants.QUEUE_CONFIG.TRACKING_TASKS_TAB_NAME,
       description: format(COPY::ALL_CASES_QUEUE_TABLE_TAB_DESCRIPTION, organization.name),
       columns: [
         Constants.QUEUE_CONFIG.CASE_DETAILS_LINK_COLUMN,
         Constants.QUEUE_CONFIG.ISSUE_COUNT_COLUMN,
         Constants.QUEUE_CONFIG.APPEAL_TYPE_COLUMN,
         Constants.QUEUE_CONFIG.DOCKET_NUMBER_COLUMN
       ],
-      task_group: Constants.QUEUE_CONFIG.TRACKING_TASKS_GROUP,
-      tasks: tasks,
       allow_bulk_assign: false
     }
   end
 
-  # rubocop:disable Metrics/AbcSize
   def unassigned_tasks_tab
-    name = Constants.QUEUE_CONFIG.UNASSIGNED_TASKS_TAB_NAME
-    tasks = TaskPager.new(assignee: organization, tab_name: name).tasks_for_tab
-
     {
-      label: format(COPY::ORGANIZATIONAL_QUEUE_PAGE_UNASSIGNED_TAB_TITLE, tasks.count),
-      name: name,
+      label: COPY::ORGANIZATIONAL_QUEUE_PAGE_UNASSIGNED_TAB_TITLE,
+      name: Constants.QUEUE_CONFIG.UNASSIGNED_TASKS_TAB_NAME,
       description: format(COPY::ORGANIZATIONAL_QUEUE_PAGE_UNASSIGNED_TASKS_DESCRIPTION, organization.name),
       # Compact to account for the maybe absent regional office column
       columns: [
@@ -94,21 +104,14 @@ def unassigned_tasks_tab
         Constants.QUEUE_CONFIG.DAYS_ON_HOLD_COLUMN,
         organization.is_a?(Representative) ? nil : Constants.QUEUE_CONFIG.DOCUMENT_COUNT_READER_LINK_COLUMN
       ].compact,
-      task_group: Constants.QUEUE_CONFIG.UNASSIGNED_TASKS_GROUP,
-      tasks: tasks,
       allow_bulk_assign: organization.can_bulk_assign_tasks?
     }
   end
-  # rubocop:enable Metrics/AbcSize
 
-  # rubocop:disable Metrics/AbcSize
   def assigned_tasks_tab
-    name = Constants.QUEUE_CONFIG.ASSIGNED_TASKS_TAB_NAME
-    tasks = TaskPager.new(assignee: organization, tab_name: name).tasks_for_tab
-
     {
-      label: format(COPY::QUEUE_PAGE_ASSIGNED_TAB_TITLE, tasks.count),
-      name: name,
+      label: COPY::QUEUE_PAGE_ASSIGNED_TAB_TITLE,
+      name: Constants.QUEUE_CONFIG.ASSIGNED_TASKS_TAB_NAME,
       description: format(COPY::ORGANIZATIONAL_QUEUE_PAGE_ASSIGNED_TASKS_DESCRIPTION, organization.name),
       # Compact to account for the maybe absent regional office column
       columns: [
@@ -121,20 +124,14 @@ def assigned_tasks_tab
         Constants.QUEUE_CONFIG.DOCKET_NUMBER_COLUMN,
         Constants.QUEUE_CONFIG.DAYS_ON_HOLD_COLUMN
       ].compact,
-      task_group: Constants.QUEUE_CONFIG.ASSIGNED_TASKS_GROUP,
-      tasks: tasks,
       allow_bulk_assign: false
     }
   end
-  # rubocop:enable Metrics/AbcSize
 
   def completed_tasks_tab
-    name = Constants.QUEUE_CONFIG.COMPLETED_TASKS_TAB_NAME
-    tasks = TaskPager.new(assignee: organization, tab_name: name).tasks_for_tab
-
     {
       label: COPY::QUEUE_PAGE_COMPLETE_TAB_TITLE,
-      name: name,
+      name: Constants.QUEUE_CONFIG.COMPLETED_TASKS_TAB_NAME,
       description: format(COPY::QUEUE_PAGE_COMPLETE_TASKS_DESCRIPTION, organization.name),
       # Compact to account for the maybe absent regional office column
       columns: [
@@ -147,8 +144,6 @@ def completed_tasks_tab
         Constants.QUEUE_CONFIG.DOCKET_NUMBER_COLUMN,
         Constants.QUEUE_CONFIG.DAYS_ON_HOLD_COLUMN
       ].compact,
-      task_group: Constants.QUEUE_CONFIG.COMPLETED_TASKS_GROUP,
-      tasks: tasks,
       allow_bulk_assign: false
     }
   end

app/models/task_pager.rb

@@ -46,14 +46,22 @@ def paged_tasks
   #   tasks
   # end
 
+  def task_page_count
+    @task_page_count ||= paged_tasks.total_pages
+  end
+
+  def total_task_count
+    @total_task_count ||= tasks_for_tab.count
+  end
+
   def tasks_for_tab
     case tab_name
     when Constants.QUEUE_CONFIG.TRACKING_TASKS_TAB_NAME
       tracking_tasks
     when Constants.QUEUE_CONFIG.UNASSIGNED_TASKS_TAB_NAME
-      unassigned_tasks
+      active_tasks
     when Constants.QUEUE_CONFIG.ASSIGNED_TASKS_TAB_NAME
-      assigned_tasks
+      on_hold_tasks
     when Constants.QUEUE_CONFIG.COMPLETED_TASKS_TAB_NAME
       recently_completed_tasks
     else
@@ -67,12 +75,12 @@ def tracking_tasks
     TrackVeteranTask.includes(*task_includes).active.where(assigned_to: assignee)
   end
 
-  def unassigned_tasks
+  def active_tasks
     Task.includes(*task_includes)
       .visible_in_queue_table_view.where(assigned_to: assignee).active
   end
 
-  def assigned_tasks
+  def on_hold_tasks
     Task.includes(*task_includes)
       .visible_in_queue_table_view.where(assigned_to: assignee).on_hold
   end