Backfill missing versions in versions manifest.

closes #907

app/services/versioned_files_service/versions_manifest.rb

@@ -30,6 +30,7 @@ def update_version(version:, version_metadata:)
       manifest[:versions][version] = version_metadata.as_json
 
       update_head_version if !version_metadata.withdrawn? && (head_version.nil? || version >= head_version)
+      backfill_withdrawn_versions
 
       write!
     end
@@ -81,7 +82,8 @@ def version_metadata_for(version:)
       check_version(version:)
 
       version_data = manifest[:versions][version]
-      VersionMetadata.new(version: version.to_i, withdrawn: version_data[:withdrawn], date: DateTime.iso8601(version_data[:date]))
+      date = version_data[:date].present? ? DateTime.iso8601(version_data[:date]) : nil
+      VersionMetadata.new(version: version.to_i, withdrawn: version_data[:withdrawn], date:)
     end
 
     def version_metadata
@@ -110,12 +112,23 @@ def manifest
     attr_reader :path
 
     def write!
+      manifest[:versions] = manifest[:versions].sort.to_h if manifest.key?(:versions)
       FileUtils.mkdir_p(path.dirname)
       path.write(manifest.to_json)
     end
 
     def check_version(version:)
       raise UnknownVersionError, "Version #{version} not found" unless version?(version:)
     end
+
+    def backfill_withdrawn_versions
+      return unless head_version
+
+      (1..head_version).each do |version|
+        next if version?(version:)
+
+        manifest[:versions][version] = { withdrawn: true, date: nil }
+      end
+    end
   end
 end

spec/services/versioned_files_service/versions_manifest_spec.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe VersionedFilesService::VersionsManifest do
+  subject(:manifest) { described_class.new(path: pathname) }
+
+  let(:pathname) { Pathname.new('tmp/versions_manifest.json') }
+
+  after do
+    pathname.delete if pathname.exist?
+  end
+
+  describe '.update_version' do
+    context 'when backfilling withdrawn versions' do
+      let(:now) { DateTime.now }
+
+      let(:expected_manifest) do
+        {
+          "$schemaVersion" => 1,
+          'head' => 3,
+          'versions' => {
+            '1' => { 'withdrawn' => true, 'date' => nil },
+            '2' => { 'withdrawn' => true, 'date' => nil },
+            '3' => { 'withdrawn' => false, 'date' => now.iso8601 }
+          }
+        }
+      end
+
+      it 'backfills withdrawn versions' do
+        manifest.update_version(version: 3, version_metadata: described_class::VersionMetadata.new(3, false, now))
+
+        expect(JSON.parse(pathname.read)).to eq expected_manifest
+      end
+    end
+  end
+end