Automatically detect and apply OS theme on Login screen (#19928)

* Automatically detect and apply OS theme in Login screen

https://community.openproject.org/work_packages/66594

* add a migration to set the default theme of anonymous user to sync_with_os

* add a migration spec

* add a feature spec

* write migrations in raw sql

* update anonymous user pref before testing the theme applied

---------

Co-authored-by: Behrokh Satarnejad <62008897+bsatarnejad@users.noreply.github.com>
Co-authored-by: Behrokh Satarnejad <b.satarnejad@openproject.com>

db/migrate/20251017111720_set_anonymous_user_theme_to_sync_with_os.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+class SetAnonymousUserThemeToSyncWithOs < ActiveRecord::Migration[8.0]
+  def up
+    say "Set anonymous user theme to sync_with_os"
+    execute <<~SQL.squish
+      UPDATE user_preferences
+      SET settings = settings || '{"theme": "sync_with_os"}'::jsonb
+      WHERE user_id = (
+        SELECT id FROM users WHERE type = 'AnonymousUser' LIMIT 1
+      );
+    SQL
+  end
+
+  def down
+    say "Rollback: Reset anonymous user theme to light"
+    execute <<~SQL.squish
+      UPDATE user_preferences
+      SET settings = settings || '{"theme": "light"}'::jsonb
+      WHERE user_id = (
+        SELECT id FROM users WHERE type = 'AnonymousUser' LIMIT 1
+      );
+    SQL
+  end
+end

spec/migrations/migrate_set_anonymous_user_theme_to_sync_with_os_spec.rb

@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+require Rails.root.join("db/migrate/20251017111720_set_anonymous_user_theme_to_sync_with_os.rb")
+
+RSpec.describe SetAnonymousUserThemeToSyncWithOs, type: :model do
+  let(:anonymous_user) { User.anonymous }
+
+  before do
+    # Ensure the anonymous user has a preference entry
+    anonymous_user.pref.update(settings: { "theme" => "light" })
+  end
+
+  describe "up migration" do
+    it "sets the anonymous user theme to sync_with_os" do
+      expect(anonymous_user.pref.settings["theme"]).to eq("light")
+
+      ActiveRecord::Migration.suppress_messages { described_class.migrate(:up) }
+
+      anonymous_user.pref.reload
+      expect(anonymous_user.pref.settings["theme"]).to eq("sync_with_os")
+    end
+
+    it "does not affect other users" do
+      other_user = create(:user)
+      other_user.pref.update(settings: { "theme" => "dark" })
+
+      ActiveRecord::Migration.suppress_messages { described_class.migrate(:up) }
+
+      other_user.pref.reload
+      expect(other_user.pref.settings["theme"]).to eq("dark")
+    end
+  end
+
+  describe "down migration" do
+    it "reverts the anonymous user theme back to light" do
+      anonymous_user.pref.update(settings: { "theme" => "sync_with_os" })
+
+      ActiveRecord::Migration.suppress_messages { described_class.migrate(:down) }
+
+      anonymous_user.pref.reload
+      expect(anonymous_user.pref.settings["theme"]).to eq("light")
+    end
+
+    it "does not modify other user preferences" do
+      other_user = create(:user)
+      other_user.pref.update(settings: { "theme" => "dark" })
+
+      ActiveRecord::Migration.suppress_messages { described_class.migrate(:down) }
+
+      other_user.pref.reload
+      expect(other_user.pref.settings["theme"]).to eq("dark")
+    end
+  end
+end

spec/views/account/login.html.erb_spec.rb

@@ -51,4 +51,22 @@ RSpec.describe "account/login" do
       expect(rendered).not_to include "Password"
     end
   end
+
+  context "if user is not logged in" do
+    before do
+      User.anonymous.pref.update(settings: { "theme" => "sync_with_os" })
+    end
+
+    it "uses the OS-synced theme preference by default" do
+      theme_data = view.user_theme_data_attributes
+
+      expect(theme_data[:auto_theme_switcher_theme_value]).to eq("sync_with_os")
+      # Check that contrast flags exist
+      expect(theme_data).to have_key(:auto_theme_switcher_force_light_contrast_value)
+      expect(theme_data).to have_key(:auto_theme_switcher_force_dark_contrast_value)
+      # Check logo classes
+      expect(theme_data[:auto_theme_switcher_desktop_light_high_contrast_logo_class]).to eq("op-logo--link_high_contrast")
+      expect(theme_data[:auto_theme_switcher_mobile_white_logo_class]).to eq("op-logo--icon_white")
+    end
+  end
 end