Allow to find epics by the given time frame

On the epics roadmap page (see #3559) we need to display epics
in the given time frame. This patch adds an additional filter to
the Epic finder which allows to filter only epics which overlap
with the given time frame, epics which do not have start and end date
set are intentionally ignored.

This filter is not used anywhere yet, but it will be used in the MR for #3559.
This patch is a separate MR to avoid overgrowing and mixing too many
things together in the frontend patch for #3559.

Related #3559

db/migrate/20180131104538_add_date_indexes_to_epics.rb

+class AddDateIndexesToEpics < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :epics, :start_date
+    add_concurrent_index :epics, :end_date
+  end
+
+  def down
+    remove_concurrent_index :epics, :start_date
+    remove_concurrent_index :epics, :end_date
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20180115201419) do
+ActiveRecord::Schema.define(version: 20180131104538) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -810,9 +810,11 @@ ActiveRecord::Schema.define(version: 20180115201419) do
 
   add_index "epics", ["assignee_id"], name: "index_epics_on_assignee_id", using: :btree
   add_index "epics", ["author_id"], name: "index_epics_on_author_id", using: :btree
+  add_index "epics", ["end_date"], name: "index_epics_on_end_date", using: :btree
   add_index "epics", ["group_id"], name: "index_epics_on_group_id", using: :btree
   add_index "epics", ["iid"], name: "index_epics_on_iid", using: :btree
   add_index "epics", ["milestone_id"], name: "index_milestone", using: :btree
+  add_index "epics", ["start_date"], name: "index_epics_on_start_date", using: :btree
 
   create_table "events", force: :cascade do |t|
     t.integer "project_id"

ee/app/finders/epics_finder.rb

@@ -10,6 +10,7 @@ class EpicsFinder < IssuableFinder
     items = by_created_at(items)
     items = by_search(items)
     items = by_author(items)
+    items = by_timeframe(items)
 
     sort(items)
   end
@@ -48,4 +49,13 @@ class EpicsFinder < IssuableFinder
       groups.select { |g| Ability.allowed?(current_user, :read_epic, g) }
     end
   end
+
+  def by_timeframe(items)
+    return items unless params[:start_date] && params[:end_date]
+
+    items
+      .where('epics.start_date is not NULL or epics.end_date is not NULL')
+      .where('epics.start_date is NULL or epics.start_date <= ?', params[:end_date].end_of_day)
+      .where('epics.end_date is NULL or epics.end_date >= ?', params[:start_date].beginning_of_day)
+  end
 end

spec/ee/spec/finders/epics_finder_spec.rb

@@ -6,8 +6,8 @@ describe EpicsFinder do
   let(:group) { create(:group, :private) }
   let(:another_group) { create(:group) }
   let!(:epic1) { create(:epic, group: group, title: 'This is awesome epic', created_at: 1.week.ago) }
-  let!(:epic2) { create(:epic, group: group, created_at: 4.days.ago, author: user) }
-  let!(:epic3) { create(:epic, group: group, description: 'not so awesome') }
+  let!(:epic2) { create(:epic, group: group, created_at: 4.days.ago, author: user, start_date: 2.days.ago) }
+  let!(:epic3) { create(:epic, group: group, description: 'not so awesome', start_date: 5.days.ago, end_date: 3.days.ago) }
   let!(:epic4) { create(:epic, group: another_group) }
 
   describe '#execute' do
@@ -89,6 +89,24 @@ describe EpicsFinder do
             expect(epics).to contain_exactly(epic1, epic2, epic3, subepic1, subepic2)
           end
         end
+
+        context 'by timeframe' do
+          it 'returns epics which start in the timeframe' do
+            expect(epics(start_date: 2.days.ago, end_date: 1.day.ago)).to contain_exactly(epic2)
+          end
+
+          it 'returns epics which end in the timeframe' do
+            expect(epics(start_date: 4.days.ago, end_date: 3.days.ago)).to contain_exactly(epic3)
+          end
+
+          it 'returns epics which start before and end after the timeframe' do
+            expect(epics(start_date: 4.days.ago, end_date: 4.days.ago)).to contain_exactly(epic3)
+          end
+
+          it 'ignores epics which do not have start and end date set' do
+            expect(epics(start_date: 2.days.ago, end_date: 1.day.ago)).not_to include(epic1)
+          end
+        end
       end
     end
   end