Allow asset to be replaced with another asset

app/controllers/assets_controller.rb

@@ -41,7 +41,7 @@ def asset_params
     exclude_blank_redirect_url(
       params
         .require(:asset)
-        .permit(:file, :draft, :redirect_url, access_limited: [])
+        .permit(:file, :draft, :redirect_url, :replacement_id, access_limited: [])
     )
   end
 

app/controllers/base_media_controller.rb

@@ -27,4 +27,8 @@ def redirect_to_draft_assets_host_for?(asset)
   def redirect_to_draft_assets_host
     redirect_to host: AssetManager.govuk.draft_assets_host, format: params[:format]
   end
+
+  def redirect_to_replacement_for(asset)
+    redirect_to asset.replacement.public_url_path, status: :moved_permanently
+  end
 end

app/controllers/media_controller.rb

@@ -25,6 +25,12 @@ def download
       return
     end
 
+    if asset.replacement.present?
+      set_expiry(cache_control)
+      redirect_to_replacement_for(asset)
+      return
+    end
+
     respond_to do |format|
       format.any do
         set_expiry(cache_control)

app/controllers/whitehall_assets_controller.rb

@@ -14,7 +14,7 @@ def asset_params
       params
         .require(:asset)
         .permit(
-          :file, :draft, :redirect_url,
+          :file, :draft, :redirect_url, :replacement_id,
           :legacy_url_path, :legacy_etag, :legacy_last_modified,
           access_limited: []
         )

app/controllers/whitehall_media_controller.rb

@@ -20,6 +20,12 @@ def download
       return
     end
 
+    if asset.replacement.present?
+      set_expiry(cache_control)
+      redirect_to_replacement_for(asset)
+      return
+    end
+
     if asset.unscanned? || asset.clean?
       set_expiry(cache_control.expires_in(1.minute))
       if asset.image?

app/models/asset.rb

@@ -6,6 +6,8 @@ class Asset
   include Mongoid::Paranoia
   include Mongoid::Timestamps
 
+  belongs_to :replacement, class_name: 'Asset', optional: true
+
   field :state, type: String, default: 'unscanned'
   field :filename_history, type: Array, default: -> { [] }
   protected :filename_history=
@@ -39,6 +41,8 @@ class Asset
                      message: 'must match the format defined in rfc4122'
                    }
 
+  validate :check_specified_replacement_exists
+
   mount_uploader :file, AssetUploader
 
   before_save :store_metadata, unless: :uploaded?
@@ -152,4 +156,10 @@ def schedule_virus_scan
   def file_stat
     File.stat(file.path)
   end
+
+  def check_specified_replacement_exists
+    if replacement_id.present? && replacement.blank?
+      errors.add(:replacement, 'not found')
+    end
+  end
 end

app/presenters/asset_presenter.rb

@@ -20,6 +20,9 @@ def as_json(options = {})
     if @asset.redirect_url.present?
       json[:redirect_url] = @asset.redirect_url
     end
+    if @asset.replacement.present?
+      json[:replacement_id] = @asset.replacement_id.to_s
+    end
     json
   end
 end

spec/controllers/assets_controller_spec.rb

@@ -107,6 +107,60 @@
         end
       end
     end
+
+    context 'when attributes include a replacement_id' do
+      let(:replacement) { FactoryBot.create(:asset) }
+      let(:replacement_id) { replacement.id.to_s }
+      let(:attributes) { valid_attributes.merge(replacement_id: replacement_id) }
+
+      it 'stores replacement asset' do
+        post :create, params: { asset: attributes }
+
+        expect(assigns(:asset).replacement).to eq(replacement)
+      end
+
+      context 'and replacement_id is blank' do
+        let(:replacement_id) { '' }
+
+        it 'stores no replacement' do
+          post :create, params: { asset: attributes }
+
+          expect(assigns(:asset).replacement).to be_blank
+        end
+
+        it 'stores replacement_id as nil' do
+          post :create, params: { asset: attributes }
+
+          expect(assigns(:asset).replacement_id).to be_nil
+        end
+      end
+
+      context 'and replacement_id does not match an existing asset' do
+        let(:replacement_id) { 'non-existent-asset-id' }
+
+        it 'responds with unprocessable entity status' do
+          post :create, params: { asset: attributes }
+
+          expect(response).to have_http_status(:unprocessable_entity)
+        end
+
+        it 'includes error message in response' do
+          post :create, params: { asset: attributes }
+
+          body = JSON.parse(response.body)
+          status = body['_response_info']['status']
+          expect(status).to include('Replacement not found')
+        end
+      end
+
+      it 'includes the replacement_id in the response' do
+        post :create, params: { asset: attributes }
+
+        body = JSON.parse(response.body)
+
+        expect(body['replacement_id']).to eq(replacement_id)
+      end
+    end
   end
 
   describe 'PUT update' do
@@ -150,6 +204,41 @@
         expect(assigns(:asset).redirect_url).to be_nil
       end
 
+      it 'stores replacement on existing asset' do
+        replacement = FactoryBot.create(:asset)
+        replacement_id = replacement.id.to_s
+        attributes = valid_attributes.merge(replacement_id: replacement_id)
+        put :update, params: { id: asset.id, asset: attributes }
+
+        expect(assigns(:asset).replacement).to eq(replacement)
+      end
+
+      it 'stores replacement_id as nil if replacement_id is blank' do
+        replacement_id = ''
+        attributes = valid_attributes.merge(replacement_id: replacement_id)
+        put :update, params: { id: asset.id, asset: attributes }
+
+        expect(assigns(:asset).replacement_id).to be_nil
+      end
+
+      it 'responds with unprocessable entity status if replacement is not found' do
+        replacement_id = 'non-existent-asset-id'
+        attributes = valid_attributes.merge(replacement_id: replacement_id)
+        put :update, params: { id: asset.id, asset: attributes }
+
+        expect(response).to have_http_status(:unprocessable_entity)
+      end
+
+      it 'includes error message in response if replacement is not found' do
+        replacement_id = 'non-existent-asset-id'
+        attributes = valid_attributes.merge(replacement_id: replacement_id)
+        put :update, params: { id: asset.id, asset: attributes }
+
+        body = JSON.parse(response.body)
+        status = body['_response_info']['status']
+        expect(status).to include('Replacement not found')
+      end
+
       it 'responds with success status' do
         put :update, params: { id: asset.id, asset: valid_attributes }
 

spec/controllers/media_controller_spec.rb

@@ -176,5 +176,28 @@
         expect(response).to redirect_to(redirect_url)
       end
     end
+
+    context 'when asset has a replacement' do
+      let(:replacement) { FactoryBot.create(:uploaded_asset) }
+      let(:asset) { FactoryBot.create(:uploaded_asset, replacement: replacement) }
+
+      it 'redirects to replacement for asset' do
+        get :download, params
+
+        expect(response).to redirect_to(replacement.public_url_path)
+      end
+
+      it 'responds with 301 moved permanently status' do
+        get :download, params
+
+        expect(response).to have_http_status(:moved_permanently)
+      end
+
+      it 'sets the Cache-Control response header to 24 hours' do
+        get :download, params
+
+        expect(response.headers['Cache-Control']).to eq('max-age=86400, public')
+      end
+    end
   end
 end

spec/controllers/whitehall_assets_controller_spec.rb

@@ -47,6 +47,14 @@
         expect(assigns(:asset).access_limited).to eq(['user-id'])
       end
 
+      it "stores replacement on asset" do
+        replacement = FactoryBot.create(:asset)
+        replacement_id = replacement.id.to_s
+        post :create, params: { asset: { replacement_id: replacement_id } }
+
+        expect(assigns(:asset).replacement).to eq(replacement)
+      end
+
       it "returns a created status" do
         post :create, params: { asset: attributes }
 

spec/controllers/whitehall_media_controller_spec.rb

@@ -116,6 +116,33 @@
       end
     end
 
+    context 'when asset has a replacement' do
+      let(:state) { 'uploaded' }
+      let(:replacement) { FactoryBot.create(:uploaded_asset) }
+
+      before do
+        asset.replacement = replacement
+      end
+
+      it 'redirects to replacement for asset' do
+        get :download, params: { path: path, format: format }
+
+        expect(response).to redirect_to(replacement.public_url_path)
+      end
+
+      it 'responds with 301 moved permanently status' do
+        get :download, params: { path: path, format: format }
+
+        expect(response).to have_http_status(:moved_permanently)
+      end
+
+      it 'sets the Cache-Control response header to 4 hours' do
+        get :download, params: { path: path, format: format }
+
+        expect(response.headers['Cache-Control']).to eq('max-age=14400, public')
+      end
+    end
+
     context 'when asset is draft and access limited' do
       let(:user) { FactoryBot.build(:user) }
       let(:state) { 'uploaded' }

spec/models/asset_spec.rb

@@ -2,14 +2,16 @@
 
 RSpec.describe Asset, type: :model do
   describe 'validation' do
-    subject(:asset) { FactoryBot.build(:asset) }
+    subject(:asset) { FactoryBot.build(:asset, attributes) }
+
+    let(:attributes) { {} }
 
     it 'is valid when built from factory' do
       expect(asset).to be_valid
     end
 
     context 'when file is not specified' do
-      subject(:asset) { FactoryBot.build(:asset, file: nil) }
+      let(:attributes) { { file: nil } }
 
       it 'is not valid' do
         expect(asset).not_to be_valid
@@ -25,6 +27,40 @@
         end
       end
     end
+
+    context 'when replacement_id is not specified' do
+      let(:attributes) { { replacement_id: nil } }
+
+      it 'is valid' do
+        expect(asset).to be_valid
+      end
+    end
+
+    context 'when replacement_id is specified' do
+      let(:attributes) { { replacement_id: replacement_id } }
+
+      context 'and replacement asset exists' do
+        let(:replacement) { FactoryBot.create(:asset) }
+        let(:replacement_id) { replacement.id.to_s }
+
+        it 'is valid' do
+          expect(asset).to be_valid
+        end
+      end
+
+      context 'and replacement asset does not exist' do
+        let(:replacement_id) { 'non-existent-asset-id' }
+
+        it 'is not valid' do
+          expect(asset).not_to be_valid
+        end
+
+        it 'includes error for replacement not found' do
+          asset.valid?
+          expect(asset.errors[:replacement]).to include('not found')
+        end
+      end
+    end
   end
 
   describe 'creation' do
@@ -845,4 +881,40 @@
       end
     end
   end
+
+  describe '#replacement' do
+    let(:asset) { FactoryBot.build(:asset, replacement: replacement) }
+
+    context 'when replacement is nil' do
+      let(:replacement) { nil }
+
+      it 'is valid' do
+        expect(asset).to be_valid
+      end
+
+      it 'has no replacement_id' do
+        expect(asset.replacement_id).to be_nil
+      end
+    end
+
+    context 'when replacement is set' do
+      let(:replacement) { FactoryBot.create(:asset) }
+
+      it 'is valid' do
+        expect(asset).to be_valid
+      end
+
+      it 'persists replacement when saved' do
+        asset.save!
+
+        expect(asset.reload.replacement).to eq(replacement)
+      end
+
+      it 'persists replacement_id when saved' do
+        asset.save!
+
+        expect(asset.reload.replacement_id).to eq(replacement.id)
+      end
+    end
+  end
 end