Make TerraformState work with object storage

- Default `file_store` to the terraform_state
  object storage setting
- Update `file_store` whenever the file changes

app/models/terraform_state.rb

@@ -5,5 +5,17 @@ class TerraformState < ApplicationRecord
 
   validates :project_id, presence: true
 
+  after_save :update_file_store, if: :saved_change_to_file?
+
   mount_uploader :file, TerraformStateUploader
+
+  def update_file_store
+    # The file.object_store is set during `uploader.store!`
+    # which happens after object is inserted/updated
+    self.update_column(:file_store, file.object_store)
+  end
+
+  def file_store
+    super || TerraformStateUploader.default_store
+  end
 end

app/uploaders/terraform_state_uploader.rb

@@ -34,5 +34,9 @@ class TerraformStateUploader < GitlabUploader
     def proxy_download_enabled?
       true
     end
+
+    def default_store
+      object_store_enabled? ? ObjectStorage::Store::REMOTE : ObjectStorage::Store::LOCAL
+    end
   end
 end

spec/models/terraform_state_spec.rb

@@ -3,7 +3,50 @@
 require 'spec_helper'
 
 describe TerraformState do
+  subject { create(:terraform_state, :with_file) }
+
   it { is_expected.to belong_to(:project) }
 
   it { is_expected.to validate_presence_of(:project_id) }
+
+  before do
+    stub_terraform_state_object_storage(TerraformStateUploader)
+  end
+
+  describe '#file_store' do
+    context 'when no value is set' do
+      it 'returns the default store of the uploader' do
+        [ObjectStorage::Store::LOCAL, ObjectStorage::Store::REMOTE].each do |store|
+          expect(TerraformStateUploader).to receive(:default_store).and_return(store)
+          expect(described_class.new.file_store).to eq(store)
+        end
+      end
+    end
+
+    context 'when a value is set' do
+      it 'returns the value' do
+        [ObjectStorage::Store::LOCAL, ObjectStorage::Store::REMOTE].each do |store|
+          expect(build(:terraform_state, file_store: store).file_store).to eq(store)
+        end
+      end
+    end
+  end
+
+  describe '#update_file_store' do
+    context 'when file is stored in object storage' do
+      it 'sets file_store to remote' do
+        expect(subject.file_store).to eq(ObjectStorage::Store::REMOTE)
+      end
+    end
+
+    context 'when file is stored locally' do
+      before do
+        stub_terraform_state_object_storage(Terraform::StateUploader, enabled: false)
+      end
+
+      it 'sets file_store to local' do
+        expect(subject.file_store).to eq(ObjectStorage::Store::LOCAL)
+      end
+    end
+  end
 end

spec/uploaders/terraform_state_uploader_spec.rb

@@ -61,4 +61,22 @@ describe TerraformStateUploader do
       expect(described_class.proxy_download_enabled?).to eq(true)
     end
   end
+
+  describe '.default_store' do
+    context 'when object storage is enabled' do
+      it 'returns REMOTE' do
+        expect(described_class.default_store).to eq(ObjectStorage::Store::REMOTE)
+      end
+    end
+
+    context 'when object storage is disabled' do
+      before do
+        stub_terraform_state_object_storage(enabled: false)
+      end
+
+      it 'returns LOCAL' do
+        expect(described_class.default_store).to eq(ObjectStorage::Store::LOCAL)
+      end
+    end
+  end
 end