Refactor the current_migration method

ee/app/models/elastic/migration_record.rb

@@ -38,7 +38,7 @@ module Elastic
     def load_from_index
       client.get(index: index_name, id: version)
     rescue StandardError => e
-      logger.error("[Elastic::MigrationRecord]: #{e.class}: #{e.message}")
+      logger.error("[#{self.class.name}]: #{e.class}: #{e.message}")
       nil
     end
 
@@ -59,6 +59,14 @@ module Elastic
       name.underscore
     end
 
+    def running?
+      started? && !stopped?
+    end
+
+    def stopped?
+      halted? || completed?
+    end
+
     def self.load_versions(completed:)
       helper = Gitlab::Elastic::Helper.default
       helper.client
@@ -67,8 +75,15 @@ module Elastic
             .map { |v| v['_id'].to_i }
     end
 
-    def running?
-      started? && !halted? && !completed?
+    def self.completed_versions
+      load_versions(completed: true)
+    end
+
+    def self.current_migration
+      completed_migrations = completed_versions
+
+      # use exclude to support new migrations which do not exist in the index yet
+      Elastic::DataMigrationService.migrations.find { |migration| completed_migrations.exclude?(migration.version) } # rubocop: disable CodeReuse/ServiceClass
     end
 
     private

ee/app/workers/elastic/migration_worker.rb

@@ -28,7 +28,7 @@ module Elastic
           helper.create_migrations_index
         end
 
-        migration = current_migration
+        migration = Elastic::MigrationRecord.current_migration
 
         unless migration
           logger.info 'MigrationWorker: no migration available'
@@ -66,6 +66,8 @@ module Elastic
 
         Elastic::DataMigrationService.drop_migration_has_finished_cache!(migration)
       end
+    rescue StandardError => e
+      logger.error("#{self.class.name}: #{e.class} #{e.message}")
     end
 
     private
@@ -88,17 +90,6 @@ module Elastic
       end
     end
 
-    def current_migration
-      completed_migrations = Elastic::MigrationRecord.load_versions(completed: true)
-
-      # use a negative condition to support new migrations which do not exist in the index yet
-      Elastic::DataMigrationService.migrations.find { |migration| !completed_migrations.include?(migration.version) }
-    rescue StandardError => e
-      # do not return a migration if there is an issue communicating with the Elasticsearch instance
-      logger.error("MigrationWorker: #{e.class}: #{e.message}")
-      nil
-    end
-
     def pause_indexing!(migration)
       return unless migration.pause_indexing?
       return if migration.load_state[:pause_indexing].present?

ee/spec/models/elastic/migration_record_spec.rb

@@ -3,6 +3,8 @@
 require 'spec_helper'
 
 RSpec.describe Elastic::MigrationRecord, :elastic do
+  using RSpec::Parameterized::TableSyntax
+
   let(:record) { described_class.new(version: Time.now.to_i, name: 'ExampleMigration', filename: nil) }
 
   describe '#save!' do
@@ -110,9 +112,30 @@ RSpec.describe Elastic::MigrationRecord, :elastic do
     end
   end
 
-  describe '#running?' do
-    using RSpec::Parameterized::TableSyntax
+  describe '#current_migration' do
+    before do
+      allow(Elastic::DataMigrationService).to receive(:migrations).and_return([record])
+      allow(described_class).to receive(:completed_versions).and_return(completed_migrations.map(&:version))
+    end
+
+    context 'when there is an unexecuted migration' do
+      let(:completed_migrations) { [] }
+
+      it 'returns the correct migration' do
+        expect(described_class.current_migration).to eq record
+      end
+    end
+
+    context 'when there are no uncompleted migrations' do
+      let(:completed_migrations) { [record] }
+
+      it 'returns nil' do
+        expect(described_class.current_migration).to be_nil
+      end
+    end
+  end
 
+  describe '#running?' do
     before do
       allow(record).to receive(:halted?).and_return(halted)
       allow(record).to receive(:started?).and_return(started)
@@ -133,4 +156,24 @@ RSpec.describe Elastic::MigrationRecord, :elastic do
       end
     end
   end
+
+  describe '#stopped?' do
+    before do
+      allow(record).to receive(:halted?).and_return(halted)
+      allow(record).to receive(:completed?).and_return(completed)
+    end
+
+    where(:halted, :completed, :expected) do
+      false | false | false
+      false | true  | true
+      true  | false | true
+      true  | true  | true
+    end
+
+    with_them do
+      it 'returns the expected result' do
+        expect(record.stopped?).to eq(expected)
+      end
+    end
+  end
 end

ee/spec/workers/elastic/migration_worker_spec.rb

@@ -26,7 +26,7 @@ RSpec.describe Elastic::MigrationWorker, :elastic do
 
       context 'an unexecuted migration present' do
         before do
-          allow(subject).to receive(:current_migration).and_return(migration)
+          allow(Elastic::MigrationRecord).to receive(:current_migration).and_return(migration)
         end
 
         it 'creates an index if it does not exist' do