DEV: Partially refactor themes controller to services (#33141)

This commit starts to introduce services to replace actions in the
ThemesController. We will start with the low langing fruit:

* Create
* Destroy
* BulkDestroy
* GetTranslations

Endpoints like #import and #update will be much harder.
Also, the https://github.com/discourse/discourse-theme-creator plugin
overrides some of these controller actions directly, so we need
to be careful.

app/controllers/admin/themes_controller.rb

@@ -192,25 +192,19 @@ class Admin::ThemesController < Admin::AdminController
   end
 
   def create
-    ban_in_allowlist_mode!
-
-    @theme =
-      Theme.new(
-        name: theme_params[:name],
-        user_id: theme_user.id,
-        user_selectable: theme_params[:user_selectable] || false,
-        color_scheme_id: theme_params[:color_scheme_id],
-        component: [true, "true"].include?(theme_params[:component]),
-      )
-    set_fields
-
-    respond_to do |format|
-      if @theme.save
-        update_default_theme
-        log_theme_change(nil, @theme)
-        format.json { render json: serialize_data(@theme, ThemeSerializer), status: :created }
-      else
-        format.json { render json: @theme.errors, status: :unprocessable_entity }
+    Themes::Create.call(
+      params: theme_params.to_unsafe_h.merge(user_id: theme_user.id),
+      guardian:,
+    ) do
+      on_success { |theme:| render json: serialize_data(theme, ThemeSerializer), status: :created }
+      on_failed_contract do |contract|
+        render json: failed_json.merge(errors: contract.errors.full_messages), status: 400
+      end
+      on_failed_policy(:ensure_remote_themes_are_not_allowlisted) { raise Discourse::InvalidAccess }
+      on_model_errors { |theme:| render json: theme.errors, status: :unprocessable_entity }
+      on_model_not_found(:theme) do |result|
+        raise Discourse::NotFound if !result.exception
+        render json: failed_json.merge(errors: result.exception.message), status: 400
       end
     end
   end
@@ -280,27 +274,23 @@ class Admin::ThemesController < Admin::AdminController
   end
 
   def destroy
-    raise Discourse::InvalidAccess if params[:id].to_i.negative?
-    @theme = Theme.find_by(id: params[:id])
-    raise Discourse::InvalidParameters.new(:id) unless @theme
-
-    StaffActionLogger.new(current_user).log_theme_destroy(@theme)
-    @theme.destroy
-
-    respond_to { |format| format.json { head :no_content } }
+    Themes::Destroy.call(service_params) do
+      on_success { render json: {}, status: :no_content }
+      on_failed_contract do |contract|
+        render json: failed_json.merge(errors: contract.errors.full_messages), status: 400
+      end
+      on_model_not_found(:theme) { raise Discourse::NotFound }
+    end
   end
 
   def bulk_destroy
-    params[:theme_ids] = params[:theme_ids].filter { |id| id.to_i.positive? }
-    themes = Theme.where(id: params[:theme_ids])
-    raise Discourse::InvalidParameters.new(:id) if themes.blank?
-
-    ActiveRecord::Base.transaction do
-      themes.each { |theme| StaffActionLogger.new(current_user).log_theme_destroy(theme) }
-      themes.destroy_all
+    Themes::BulkDestroy.call(service_params) do
+      on_success { render json: {}, status: :no_content }
+      on_failed_contract do |contract|
+        render json: failed_json.merge(errors: contract.errors.full_messages), status: 400
+      end
+      on_model_not_found(:themes) { raise Discourse::NotFound }
     end
-
-    respond_to { |format| format.json { head :no_content } }
   end
 
   def show
@@ -326,22 +316,14 @@ class Admin::ThemesController < Admin::AdminController
   end
 
   def get_translations
-    params.require(:locale)
-    if I18n.available_locales.exclude?(params[:locale].to_sym)
-      raise Discourse::InvalidParameters.new(:locale)
-    end
-
-    I18n.locale = params[:locale]
-
-    @theme = Theme.find_by(id: params[:id])
-    raise Discourse::InvalidParameters.new(:id) unless @theme
-
-    translations =
-      @theme.translations.map do |translation|
-        { key: translation.key, value: translation.value, default: translation.default }
+    Themes::GetTranslations.call(service_params) do
+      on_success { |translations:| render(json: success_json.merge(translations:)) }
+      on_failed_contract do |contract|
+        render json: failed_json.merge(errors: contract.errors.full_messages), status: 400
       end
-
-    render json: { translations: translations }, status: :ok
+      on_failed_policy(:validate_locale) { raise Discourse::InvalidParameters.new(:locale) }
+      on_model_not_found(:theme) { raise Discourse::NotFound }
+    end
   end
 
   def update_single_setting
@@ -408,7 +390,7 @@ class Admin::ThemesController < Admin::AdminController
   def update_default_theme
     if theme_params.key?(:default)
       is_default = theme_params[:default].to_s == "true"
-      if @theme.id == SiteSetting.default_theme_id && !is_default
+      if @theme.default? && !is_default
         Theme.clear_default!
       elsif is_default
         @theme.set_default!

app/models/theme.rb

@@ -21,6 +21,12 @@ class Theme < ActiveRecord::Base
   class SettingsMigrationError < StandardError
   end
 
+  class InvalidFieldTargetError < StandardError
+  end
+
+  class InvalidFieldTypeError < StandardError
+  end
+
   attr_accessor :child_components
   attr_accessor :skip_child_components_update
 
@@ -630,11 +636,21 @@ class Theme < ActiveRecord::Base
     name = name.to_s
 
     target_id = Theme.targets[target.to_sym]
-    raise "Unknown target #{target} passed to set field" unless target_id
+    if target_id.blank?
+      raise InvalidFieldTargetError.new("Unknown target #{target} passed to set field")
+    end
 
     type_id ||=
       type ? ThemeField.types[type.to_sym] : ThemeField.guess_type(name: name, target: target)
-    raise "Unknown type #{type} passed to set field" unless type_id
+    if type_id.blank?
+      if type.present?
+        raise InvalidFieldTypeError.new("Unknown type #{type} passed to set field")
+      else
+        raise InvalidFieldTypeError.new(
+                "No type could be guessed for field #{name} for target #{target}",
+              )
+      end
+    end
 
     value ||= ""
 

app/models/theme_field.rb

@@ -3,7 +3,8 @@
 class ThemeField < ActiveRecord::Base
   MIGRATION_NAME_PART_MAX_LENGTH = 150
 
-  # This string is not 'secret'. It's just randomized to avoid accidental clashes with genuine theme field content.
+  # This string is not 'secret'. It's just randomized to avoid accidental
+  # clashes with genuine theme field content.
   CSP_NONCE_PLACEHOLDER = "__CSP__NONCE__PLACEHOLDER__f72bff1b1768168a34ee092ce759f192__"
 
   belongs_to :upload

app/services/themes/bulk_destroy.rb

@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+# Destroys multiple themes and logs the staff action. Related records are destroyed
+# by ActiveRecord dependent: :destroy. Cannot be used to destroy system themes.
+#
+# @example
+#  Themes::Destroy.call(
+#    guardian: guardian,
+#    params: {
+#      theme_ids: [theme_1.id, theme_2.id],
+#    }
+#  )
+#
+class Themes::BulkDestroy
+  include Service::Base
+
+  # @!method self.call(guardian:, params:)
+  #   @param [guardian] guardian
+  #   @param [hash] params
+  #   @option params [array] :theme_ids The ids of the themes to destroy, must be positive integers.
+  #   @return [service::base::context]
+
+  params do
+    attribute :theme_ids, :array
+    validates :theme_ids, presence: true, length: { minimum: 1, maximum: 50 }
+    validate :theme_ids_must_be_positive, if: -> { theme_ids.present? }
+
+    before_validation { self.theme_ids = theme_ids.map(&:to_i).uniq if theme_ids.present? }
+
+    def theme_ids_must_be_positive
+      return if theme_ids.all?(&:positive?)
+      errors.add(:theme_ids, I18n.t("errors.messages.must_all_be_positive"))
+    end
+  end
+
+  model :themes
+
+  transaction do
+    step :log_themes_destroy
+    step :destroy_themes
+  end
+
+  private
+
+  def fetch_themes(params:)
+    Theme.where(id: params.theme_ids)
+  end
+
+  def log_themes_destroy(themes:, guardian:)
+    staff_action_logger = StaffActionLogger.new(guardian.user)
+    themes.each { |theme| staff_action_logger.log_theme_destroy(theme) }
+  end
+
+  def destroy_themes(themes:)
+    themes.destroy_all
+  end
+end

app/services/themes/create.rb

@@ -0,0 +1,85 @@
+# frozen_string_literal: true
+
+# Creates a new theme with the provided parameters. Themes can be created
+# with various attributes including name, user selectability, color scheme,
+# and theme fields.
+#
+# Also used to create theme components.
+#
+# The theme can optionally be set as the default theme, overriding SiteSetting.default_theme_id.
+# The theme will then be used for all users on the site who haven't specifically set their
+# theme preference.
+#
+# @example
+#  Themes::Create.call(
+#    guardian: guardian,
+#    params: {
+#      name: "My Theme",
+#      user_selectable: true,
+#      color_scheme_id: 1,
+#      component: false,
+#      theme_fields: [
+#        { name: "header", target: "common", value: "content", type_id: 1 }
+#      ],
+#      default: false
+#    }
+#  )
+#
+
+class Themes::Create
+  include Service::Base
+
+  # @!method self.call(guardian:, params:)
+  #   @param [Guardian] guardian
+  #   @param [Hash] params
+  #   @option params String :name The name of the theme
+  #   @option params Integer :user_id The ID of the user creating the theme
+  #   @option params [Boolean] :user_selectable Whether the theme can be selected by users
+  #   @option params [Integer] :color_scheme_id The ID of the color palette to use
+  #   @option params [Boolean] :component Whether this is a theme component. These cannot be user_selectable or have a color_scheme_id
+  #   @option params [Array] :theme_fields Array of theme field attributes
+  #   @option params [Boolean] :default Whether to set this as the default theme
+  #   @return [Service::Base::Context]
+
+  params do
+    attribute :name, :string
+    attribute :user_id, :integer
+    attribute :user_selectable, :boolean, default: false
+    attribute :color_scheme_id, :integer
+    attribute :component, :boolean, default: false
+    attribute :theme_fields, :array
+    attribute :default, :boolean, default: false
+
+    validates :name, presence: true
+    validates :user_id, presence: true
+    validates :theme_fields, length: { maximum: 100 }
+  end
+
+  policy :ensure_remote_themes_are_not_allowlisted
+
+  transaction do
+    model :theme, :create_theme
+    step :update_default_theme
+    step :log_theme_change
+  end
+
+  private
+
+  def ensure_remote_themes_are_not_allowlisted
+    Theme.allowed_remote_theme_ids.nil?
+  end
+
+  def create_theme(params:)
+    Theme.create(
+      params.slice(:name, :user_id, :user_selectable, :color_scheme_id, :component),
+    ) { |theme| params.theme_fields.to_a.each { |field| theme.set_field(**field.symbolize_keys) } }
+  end
+
+  def update_default_theme(params:, theme:)
+    theme.set_default! if params.default
+  end
+
+  def log_theme_change(theme:, guardian:)
+    StaffActionLogger.new(guardian.user).log_theme_change(nil, theme)
+  end
+end

app/services/themes/destroy.rb

@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+# Destroys a theme and logs the staff action. Related records are destroyed
+# by ActiveRecord dependent: :destroy. Cannot be used to destroy system themes.
+#
+# @example
+#  Themes::Destroy.call(
+#    guardian: guardian,
+#    params: {
+#      id: theme.id,
+#    }
+#  )
+#
+class Themes::Destroy
+  include Service::Base
+
+  # @!method self.call(guardian:, params:)
+  #   @param [Guardian] guardian
+  #   @param [Hash] params
+  #   @option params [Integer] :id The ID of the theme to destroy, must be greater than 0.
+  #   @return [Service::Base::Context]
+
+  params do
+    attribute :id, :integer
+
+    # Negative theme IDs are for system themes only, which cannot be destroyed.
+    validates :id, presence: true, numericality: { only_integer: true, greater_than: 0 }
+  end
+
+  model :theme
+
+  transaction do
+    step :destroy_theme
+    step :log_theme_destroy
+  end
+
+  private
+
+  def fetch_theme(params:)
+    Theme.find_by(id: params.id)
+  end
+
+  def destroy_theme(theme:)
+    theme.destroy
+  end
+
+  def log_theme_destroy(theme:, guardian:)
+    StaffActionLogger.new(guardian.user).log_theme_destroy(theme)
+  end
+end

app/services/themes/get_translations.rb

@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+# Gets all of the translation overrides for a theme, which are defined
+# in locale yml files for a theme. A ThemeField is created for each locale,
+# which in turn creates ThemeTranslationOverride records.
+#
+# @example
+#  Themes::GetTranslations.call(
+#    guardian: guardian,
+#    params: {
+#      id: theme.id,
+#      locale: "en",
+#    }
+#  )
+#
+class Themes::GetTranslations
+  include Service::Base
+
+  params do
+    attribute :locale, :string
+    attribute :id, :integer
+
+    validates :id, presence: true
+    validates :locale, presence: true
+
+    validate :validate_locale, if: -> { locale.present? }
+
+    def validate_locale
+      return if I18n.available_locales.include?(locale.to_sym)
+      errors.add(:base, I18n.t("errors.messages.invalid_locale", invalid_locale: locale))
+    end
+  end
+
+  model :theme
+  model :translations
+
+  private
+
+  def fetch_theme(params:)
+    Theme.find_by(id: params.id)
+  end
+
+  def fetch_translations(theme:, params:)
+    I18n.with_locale(params.locale) do
+      theme.translations.map do |translation|
+        { key: translation.key, value: translation.value, default: translation.default }
+      end
+    end
+  end
+end

config/locales/server.en.yml

@@ -283,6 +283,7 @@ en:
     format: ! "%{attribute} %{message}"
     format_with_full_message: "<b>%{attribute}</b>: %{message}"
     messages:
+      invalid_locale: "%{invalid_locale} is not a valid locale"
       too_long_validation:
         one: "is limited to %{count} character; you entered %{length}."
         other: "is limited to %{count} characters; you entered %{length}."
@@ -312,6 +313,7 @@ en:
       less_than_or_equal_to: must be less than or equal to %{count}
       not_a_number: is not a number
       not_an_integer: must be an integer
+      must_all_be_positive: must all be positive
       odd: must be odd
       record_invalid: ! "Validation failed: %{errors}"
       max_emojis: "can't have more than %{max_emojis_count} emoji"

spec/requests/admin/themes_controller_spec.rb

@@ -573,7 +573,7 @@ RSpec.describe Admin::ThemesController do
     context "when logged in as an admin" do
       before { sign_in(admin) }
 
-      it "creates a theme" do
+      it "creates a theme and theme fields" do
         post "/admin/themes.json",
              params: {
                theme: {
@@ -589,6 +589,51 @@ RSpec.describe Admin::ThemesController do
         expect(json["theme"]["theme_fields"].length).to eq(1)
         expect(UserHistory.where(action: UserHistory.actions[:change_theme]).count).to eq(1)
       end
+
+      it "can set a theme to default" do
+        post "/admin/themes.json", params: { theme: { name: "my test name", default: "true" } }
+
+        expect(response.status).to eq(201)
+
+        json = response.parsed_body
+        expect(json["theme"]["default"]).to eq(true)
+      end
+
+      context "when creating a theme field with an invalid target" do
+        it "errors" do
+          post "/admin/themes.json",
+               params: {
+                 theme: {
+                   name: "my test name",
+                   theme_fields: [name: "scss", target: "blah", value: "body{color: red;}"],
+                 },
+               }
+
+          expect(response.status).to eq(400)
+
+          json = response.parsed_body
+          expect(json["errors"]).to include("Unknown target blah passed to set field")
+        end
+      end
+
+      context "when creating a theme field with an invalid type" do
+        it "errors" do
+          post "/admin/themes.json",
+               params: {
+                 theme: {
+                   name: "my test name",
+                   theme_fields: [name: "blahblah", target: "common", value: "body{color: red;}"],
+                 },
+               }
+
+          expect(response.status).to eq(400)
+
+          json = response.parsed_body
+          expect(json["errors"]).to include(
+            "No type could be guessed for field blahblah for target common",
+          )
+        end
+      end
     end
 
     shared_examples "theme creation not allowed" do
@@ -619,6 +664,20 @@ RSpec.describe Admin::ThemesController do
 
       include_examples "theme creation not allowed"
     end
+
+    context "when theme allowlist mode is enabled" do
+      before do
+        global_setting :allowed_theme_repos, "  https://magic.com/repo.git, https://x.com/git"
+      end
+
+      it "prevents theme creation with 404 error" do
+        expect do
+          post "/admin/themes.json", params: { theme: { name: "my test name" } }
+        end.not_to change { Theme.count }
+
+        expect(response.status).to eq(404)
+      end
+    end
   end
 
   describe "#update" do
@@ -1066,7 +1125,7 @@ RSpec.describe Admin::ThemesController do
       it "returns the right response when an invalid id is given" do
         delete "/admin/themes/9999.json"
 
-        expect(response.status).to eq(400)
+        expect(response.status).to eq(404)
       end
 
       it "deletes the field's javascript cache" do
@@ -1401,7 +1460,7 @@ RSpec.describe Admin::ThemesController do
         get "/admin/themes/#{theme.id}/translations/foo.json"
         expect(response.status).to eq(400)
         expect(response.parsed_body["errors"]).to include(
-          I18n.t("invalid_params", message: :locale),
+          I18n.t("errors.messages.invalid_locale", invalid_locale: "foo"),
         )
       end
     end
@@ -1438,19 +1497,24 @@ RSpec.describe Admin::ThemesController do
       expect do
         delete "/admin/themes/bulk_destroy.json", params: { theme_ids: theme_ids }
       end.to change { Theme.count }.by(-2)
+      expect(response.status).to eq(204)
     end
 
-    it "does not destroy if any theme is system" do
+    it "does not destroy any themes if any of them is a system theme" do
       theme.update_columns(id: -10)
       expect do
         delete "/admin/themes/bulk_destroy.json", params: { theme_ids: theme_ids }
-      end.to change { Theme.count }.by(-1)
-      expect { theme_2.reload }.to raise_exception(ActiveRecord::RecordNotFound)
+      end.not_to change { Theme.count }
+      expect(response.status).to eq(400)
+      expect(response.parsed_body["errors"]).to eq(
+        ["Theme ids " + I18n.t("errors.messages.must_all_be_positive")],
+      )
     end
 
     it "logs the theme destroy action for each theme" do
       StaffActionLogger.any_instance.expects(:log_theme_destroy).twice
       delete "/admin/themes/bulk_destroy.json", params: { theme_ids: theme_ids }
+      expect(response.status).to eq(204)
     end
   end
 

spec/services/themes/bulk_destroy_spec.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+RSpec.describe Themes::BulkDestroy do
+  describe described_class::Contract, type: :model do
+    it { is_expected.to validate_presence_of(:theme_ids) }
+    it { is_expected.to allow_values([1], (1..50).to_a).for(:theme_ids) }
+    it { is_expected.not_to allow_values([], (1..51).to_a).for(:theme_ids) }
+    it do
+      is_expected.not_to allow_values([1, 0, -3]).for(:theme_ids).with_message(
+        /must all be positive/,
+      )
+    end
+  end
+
+  describe ".call" do
+    subject(:result) { described_class.call(params:, **dependencies) }
+
+    fab!(:theme_1) { Fabricate(:theme) }
+    fab!(:theme_2) { Fabricate(:theme) }
+    fab!(:admin)
+
+    let(:params) { { theme_ids: [theme_1.id, theme_2.id] } }
+    let(:dependencies) { { guardian: admin.guardian } }
+
+    context "when data is invalid" do
+      let(:params) { {} }
+
+      it { is_expected.to fail_a_contract }
+    end
+
+    context "when a theme does not exist" do
+      before do
+        theme_1.destroy!
+        theme_2.destroy!
+      end
+
+      it { is_expected.to fail_to_find_a_model(:themes) }
+    end
+
+    context "when everything is ok" do
+      it { is_expected.to run_successfully }
+
+      it "destroys the themes" do
+        expect { result }.to change { Theme.count }.by(-2)
+      end
+
+      it "logs the theme destroys" do
+        expect_any_instance_of(StaffActionLogger).to receive(:log_theme_destroy).with(theme_1).once
+        expect_any_instance_of(StaffActionLogger).to receive(:log_theme_destroy).with(theme_2).once
+        result
+      end
+    end
+  end
+end

spec/services/themes/create_spec.rb

@@ -0,0 +1,156 @@
+# frozen_string_literal: true
+
+RSpec.describe Themes::Create do
+  describe described_class::Contract, type: :model do
+    it { is_expected.to validate_presence_of(:name) }
+    it { is_expected.to validate_presence_of(:user_id) }
+    it { is_expected.to validate_length_of(:theme_fields).as_array.is_at_least(0).is_at_most(100) }
+  end
+
+  describe ".call" do
+    subject(:result) { described_class.call(params:, **dependencies) }
+
+    fab!(:user)
+    fab!(:admin)
+    fab!(:guardian) { admin.guardian }
+    fab!(:color_scheme)
+
+    let(:dependencies) { { guardian: } }
+
+    let(:theme_params) do
+      {
+        name: "My Cool Theme",
+        user_id: admin.id,
+        user_selectable: true,
+        color_scheme_id: color_scheme.id,
+        component: false,
+        theme_fields: [
+          {
+            name: "header",
+            target: "common",
+            value: "header content",
+            type_id: ThemeField.types[:html],
+          },
+        ],
+        default: false,
+      }
+    end
+
+    let(:params) { theme_params }
+
+    context "when remote themes are allowlisted" do
+      before do
+        GlobalSetting.stubs(:allowed_theme_repos).returns(
+          "https://github.com/discourse/sample-theme",
+        )
+      end
+
+      it { is_expected.to fail_a_policy(:ensure_remote_themes_are_not_allowlisted) }
+    end
+
+    context "with invalid theme field target" do
+      let(:params) do
+        theme_params.merge(
+          theme_fields: [
+            { name: "header", target: "invalid_target", value: "header content", type: "html" },
+          ],
+        )
+      end
+
+      it { is_expected.to fail_to_find_a_model(:theme) }
+    end
+
+    context "with invalid theme field type" do
+      let(:params) do
+        theme_params.merge(
+          theme_fields: [
+            {
+              name: "header",
+              target: "common",
+              value: "header content",
+              type: "blah", # Invalid type
+            },
+          ],
+        )
+      end
+
+      it { is_expected.to fail_to_find_a_model(:theme) }
+    end
+
+    context "with invalid component model parameters" do
+      let(:params) { theme_params.merge(component: true) }
+
+      it "fails to create a component" do
+        expect(result).to fail_with_an_invalid_model(:theme)
+        expect(result.theme.errors.full_messages).to eq(
+          [
+            "Theme components can't have color palettes",
+            "Theme components can't be user-selectable",
+          ],
+        )
+      end
+    end
+
+    context "when everything is ok" do
+      it { is_expected.to run_successfully }
+
+      it "creates a theme with the provided parameters" do
+        expect(result.theme).to have_attributes(
+          name: "My Cool Theme",
+          user_id: admin.id,
+          user_selectable: true,
+          color_scheme_id: color_scheme.id,
+          component: false,
+          theme_fields: [have_attributes(name: "header", value: "header content")],
+        )
+      end
+
+      it "logs the theme change" do
+        expect_any_instance_of(StaffActionLogger).to receive(:log_theme_change).with(
+          nil,
+          an_instance_of(Theme),
+        )
+        result
+      end
+
+      context "with component param" do
+        let(:params) do
+          theme_params.merge(component: true, user_selectable: false, color_scheme_id: nil)
+        end
+
+        it "creates a component" do
+          expect(result.theme).to be_a_component
+        end
+      end
+
+      context "with empty theme_fields" do
+        let(:params) { theme_params.except(:theme_fields) }
+
+        it "creates a theme without fields" do
+          expect(result.theme.theme_fields).to be_empty
+        end
+      end
+
+      context "when default param is true" do
+        let(:params) { theme_params.merge(default: true) }
+
+        it "sets the theme as default" do
+          expect(result.theme).to be_default
+          expect(SiteSetting.default_theme_id).to eq(result.theme.id)
+        end
+
+        context "when there is an existing default theme" do
+          fab!(:existing_default) { Fabricate(:theme) }
+
+          before { existing_default.set_default! }
+
+          it "clears the existing default theme" do
+            expect { result }.to change { existing_default.reload.default? }.to(false)
+            expect(result.theme).to be_default
+            expect(SiteSetting.default_theme_id).to eq(result.theme.id)
+          end
+        end
+      end
+    end
+  end
+end

spec/services/themes/destroy_spec.rb

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+RSpec.describe Themes::Destroy do
+  describe described_class::Contract, type: :model do
+    it { is_expected.to validate_presence_of(:id) }
+    it { is_expected.to allow_values(1, "1", 42).for(:id) }
+    it { is_expected.not_to allow_values(-1, 0).for(:id) }
+  end
+
+  describe ".call" do
+    subject(:result) { described_class.call(params:, **dependencies) }
+
+    fab!(:theme)
+    fab!(:admin)
+
+    let(:params) { { id: theme.id } }
+    let(:dependencies) { { guardian: admin.guardian } }
+
+    context "when data is invalid" do
+      let(:params) { {} }
+
+      it { is_expected.to fail_a_contract }
+    end
+
+    context "for invalid theme id" do
+      before { theme.destroy! }
+
+      it { is_expected.to fail_to_find_a_model(:theme) }
+    end
+
+    context "when everything is ok" do
+      it { is_expected.to run_successfully }
+
+      it "destroys the theme" do
+        expect { result }.to change { Theme.find_by(id: theme.id) }.to(nil)
+      end
+
+      it "logs the theme destroy" do
+        expect_any_instance_of(StaffActionLogger).to receive(:log_theme_destroy).with(theme)
+        result
+      end
+    end
+  end
+end

spec/services/themes/get_translations_spec.rb

@@ -0,0 +1,77 @@
+# frozen_string_literal: true
+
+RSpec.describe Themes::GetTranslations do
+  describe described_class::Contract, type: :model do
+    it { is_expected.to validate_presence_of :id }
+    it { is_expected.to validate_presence_of :locale }
+
+    context "when locale is invalid" do
+      let(:locale) { "invalid_locale" }
+
+      it "invalidates the contract" do
+        contract = described_class.new(locale: locale)
+        contract.validate
+        expect(contract.errors.full_messages).to include(
+          I18n.t("errors.messages.invalid_locale", invalid_locale: locale),
+        )
+      end
+    end
+  end
+
+  describe ".call" do
+    subject(:result) { described_class.call(params:) }
+
+    fab!(:theme)
+    fab!(:locale_field_1) do
+      ThemeField.create!(
+        theme_id: theme.id,
+        name: "en",
+        type_id: ThemeField.types[:yaml],
+        target_id: Theme.targets[:translations],
+        value: <<~YAML,
+        en:
+          theme_metadata:
+            description: "Description of my theme"
+          skip_to_main_content: "Skip to main contentzz"
+          skip_user_nav: "Skip to profile contentzz"
+      YAML
+      )
+    end
+
+    let(:locale) { I18n.available_locales.first.to_s }
+    let(:params) { { id: theme.id, locale: locale } }
+
+    context "when data is invalid" do
+      let(:params) { {} }
+
+      it { is_expected.to fail_a_contract }
+    end
+
+    context "when theme doesn't exist" do
+      before { theme.destroy! }
+
+      it { is_expected.to fail_to_find_a_model(:theme) }
+    end
+
+    context "when everything is ok" do
+      it { is_expected.to run_successfully }
+
+      it "returns the theme translations" do
+        expect(result.translations).to eq(
+          [
+            {
+              key: "skip_to_main_content",
+              value: "Skip to main contentzz",
+              default: "Skip to main contentzz",
+            },
+            {
+              key: "skip_user_nav",
+              value: "Skip to profile contentzz",
+              default: "Skip to profile contentzz",
+            },
+          ],
+        )
+      end
+    end
+  end
+end