Add Mobility gem and configure text fields to be translatable

Gemfile

@@ -133,3 +133,5 @@ group :test do
   gem "parallel_rspec"
   gem "spring-prspec"
 end
+
+gem "mobility", "~> 1.3"

Gemfile.lock

@@ -286,6 +286,9 @@ GEM
     matrix (0.4.2)
     mini_mime (1.1.5)
     minitest (5.25.5)
+    mobility (1.3.2)
+      i18n (>= 0.6.10, < 2)
+      request_store (~> 1.0)
     msgpack (1.8.0)
     multi_xml (0.7.2)
       bigdecimal (~> 3.1)
@@ -623,6 +626,7 @@ DEPENDENCIES
   govuk_notify_rails
   i18n-tasks (~> 1.0.15)
   lograge
+  mobility (~> 1.3)
   omniauth-auth0
   omniauth-rails_csrf_protection
   pagy
@@ -741,6 +745,7 @@ CHECKSUMS
   matrix (0.4.2) sha256=71083ccbd67a14a43bfa78d3e4dc0f4b503b9cc18e5b4b1d686dc0f9ef7c4cc0
   mini_mime (1.1.5) sha256=8681b7e2e4215f2a159f9400b5816d85e9d8c6c6b491e96a12797e798f8bccef
   minitest (5.25.5) sha256=391b6c6cb43a4802bfb7c93af1ebe2ac66a210293f4a3fb7db36f2fc7dc2c756
+  mobility (1.3.2) sha256=32fbbb0e53118ef42de20daa6ac94dbb758c628874092eba311b968a1e1d757b
   msgpack (1.8.0) sha256=e64ce0212000d016809f5048b48eb3a65ffb169db22238fb4b72472fecb2d732
   multi_xml (0.7.2) sha256=307a96dc48613badb7b2fc174fd4e62d7c7b619bc36ea33bfd0c49f64f5787ce
   mutex_m (0.3.0) sha256=cfcb04ac16b69c4813777022fdceda24e9f798e48092a2b817eb4c0a782b0751

app/models/condition.rb

@@ -1,5 +1,7 @@
 class Condition < ApplicationRecord
   include ConditionMethods
+  extend Mobility
+
   belongs_to :routing_page, class_name: "Page"
   belongs_to :check_page, class_name: "Page", optional: true
   belongs_to :goto_page, class_name: "Page", optional: true
@@ -8,6 +10,10 @@ class Condition < ApplicationRecord
 
   before_destroy :destroy_postconditions
 
+  translates :answer_value,
+             :exit_page_heading
+  translates :exit_page_markdown, presence: false # Without presence here, the value is nil if set to ""
+
   def self.create_and_update_form!(...)
     condition = Condition.new(...)
     condition.save_and_update_form

app/models/form.rb

@@ -1,5 +1,6 @@
 class Form < ApplicationRecord
   include FormStateMachine
+  extend Mobility
 
   has_many :pages, -> { order(position: :asc) }, dependent: :destroy
   has_one :form_submission_email, dependent: :destroy
@@ -10,6 +11,16 @@ class Form < ApplicationRecord
   has_one :draft_form_document, -> { where tag: "draft" }, class_name: "FormDocument"
   has_many :conditions, through: :pages, source: :routing_conditions
 
+  translates :name,
+             :privacy_policy_url,
+             :support_email,
+             :support_phone,
+             :support_url,
+             :support_url_text,
+             :declaration_text,
+             :what_happens_next_markdown,
+             :payment_url
+
   enum :submission_type, {
     email: "email",
     email_with_csv: "email_with_csv",
@@ -56,9 +67,13 @@ def has_been_archived
 
   alias_method :is_archived?, :has_been_archived
 
-  def name=(val)
-    super(val)
-    self[:form_slug] = name.parameterize
+  # We need to include the splat operator as second argument,
+  # since Mobility expects this when using locale setters like `name_cy=`
+  def name=(val, ...)
+    super
+
+    # Always set form_slug using the English name
+    self[:form_slug] = name_en.parameterize
   end
 
   # form_slug is always set based on name

app/models/page.rb

@@ -1,4 +1,5 @@
 class Page < ApplicationRecord
+  extend Mobility
   before_destroy :destroy_secondary_skip_conditions
 
   belongs_to :form
@@ -7,6 +8,12 @@ class Page < ApplicationRecord
   has_many :goto_conditions, class_name: "Condition", foreign_key: "goto_page_id", dependent: :destroy
   acts_as_list scope: :form
 
+  translates :question_text,
+             :hint_text,
+             :answer_settings,
+             :page_heading,
+             :guidance_markdown
+
   ANSWER_TYPES = %w[name organisation_name email phone_number national_insurance_number address date selection number text file].freeze
 
   ANSWER_TYPES_WITHOUT_SETTINGS = %w[organisation_name email phone_number national_insurance_number number].freeze
@@ -24,6 +31,10 @@ class Page < ApplicationRecord
   validate :guidance_markdown_length_and_tags
 
   attribute :answer_settings, DataStructType.new
+  # Open the Model class used for tanslations and make the same change to the answer_settings attribute
+  class Translation
+    attribute :answer_settings, DataStructType.new
+  end
 
   def self.create_and_update_form!(...)
     page = Page.new(...)

config/application.rb

@@ -71,5 +71,9 @@ class Application < Rails::Application
 
     # Include full precision of timestamps in JSON responses
     config.active_support.time_precision = 6
+
+    # Turn off locale enforcement - this allows us to use locales
+    # in Mobility without enabling those languages for the admin UI
+    I18n.enforce_available_locales = false
   end
 end

config/initializers/mobility.rb

@@ -0,0 +1,129 @@
+Mobility.configure do
+  # PLUGINS
+  plugins do
+    # Backend
+    #
+    # Sets the default backend to use in models. This can be overridden in models
+    # by passing +backend: ...+ to +translates+.
+    #
+    # To default to a different backend globally, replace +:key_value+ by another
+    # backend name.
+    #
+    backend :table
+
+    # ActiveRecord
+    #
+    # Defines ActiveRecord as ORM, and enables ActiveRecord-specific plugins.
+    active_record
+
+    # Accessors
+    #
+    # Define reader and writer methods for translated attributes. Remove either
+    # to disable globally, or pass +reader: false+ or +writer: false+ to
+    # +translates+ in any translated model.
+    #
+    reader
+    writer
+
+    # Backend Reader
+    #
+    # Defines reader to access the backend for any attribute, of the form
+    # +<attribute>_backend+.
+    #
+    backend_reader
+    #
+    # Or pass an interpolation string to define a different pattern:
+    # backend_reader "%s_translations"
+
+    # Query
+    #
+    # Defines a scope on the model class which allows querying on
+    # translated attributes. The default scope is named +i18n+, pass a different
+    # name as default to change the global default, or to +translates+ in any
+    # model to change it for that model alone.
+    #
+    query
+
+    # Cache
+    #
+    # Comment out to disable caching reads and writes.
+    #
+    cache
+
+    # Dirty
+    #
+    # Uncomment this line to include and enable globally:
+    # dirty
+    #
+    # Or uncomment this line to include but disable by default, and only enable
+    # per model by passing +dirty: true+ to +translates+.
+    # dirty false
+
+    # Column Fallback
+    #
+    # Uncomment line below to fallback to original column. You can pass
+    # +column_fallback: true+ to +translates+ to return original column on
+    # default locale, or pass +column_fallback: [:en, :de]+ to +translates+
+    # to return original column for those locales or pass
+    # +column_fallback: ->(locale) { ... }+ to +translates to evaluate which
+    # locales to return original column for.
+    # column_fallback
+    #
+    # Or uncomment this line to enable column fallback with a global default.
+    column_fallback true
+
+    # Fallbacks
+    #
+    # Uncomment line below to enable fallbacks, using +I18n.fallbacks+.
+    # fallbacks
+    #
+    # Or uncomment this line to enable fallbacks with a global default.
+    fallbacks(cy: :en)
+
+    # Presence
+    #
+    # Converts blank strings to nil on reads and writes. Comment out to
+    # disable.
+    #
+    presence
+
+    # Default
+    #
+    # Set a default translation per attributes. When enabled, passing +default:
+    # 'foo'+ sets a default translation string to show in case no translation is
+    # present. Can also be passed a proc.
+    #
+    # default 'foo'
+
+    # Fallthrough Accessors
+    #
+    # Uses method_missing to define locale-specific accessor methods like
+    # +title_en+, +title_en=+, +title_fr+, +title_fr=+ for each translated
+    # attribute. If you know what set of locales you want to support, it's
+    # generally better to use Locale Accessors (or both together) since
+    # +method_missing+ is very slow.  (You can use both fallthrough and locale
+    # accessor plugins together without conflict.)
+    #
+    # fallthrough_accessors
+
+    # Locale Accessors
+    #
+    # Uses +def+ to define accessor methods for a set of locales. By default uses
+    # +I18n.available_locales+, but you can pass the set of locales with
+    # +translates+ and/or set a global default here.
+    #
+    # locale_accessors
+    #
+    # Or define specific defaults by uncommenting line below
+    locale_accessors %i[en cy]
+
+    # Attribute Methods
+    #
+    # Adds translated attributes to +attributes+ hash, and defines methods
+    # +translated_attributes+ and +untranslated_attributes+ which return hashes
+    # with translated and untranslated attributes, respectively. Be aware that
+    # this plugin can create conflicts with other gems.
+    #
+    # attribute_methods
+  end
+end

db/migrate/20251007133521_create_form_translations_for_mobility_table_backend.rb

@@ -0,0 +1,24 @@
+class CreateFormTranslationsForMobilityTableBackend < ActiveRecord::Migration[8.0]
+  def change
+    create_table :form_translations do |t|
+      # Translated attribute(s)
+      t.text :name
+      t.text :privacy_policy_url
+      t.text :support_email
+      t.text :support_phone
+      t.text :support_url
+      t.text :support_url_text
+      t.text :declaration_text
+      t.text :what_happens_next_markdown
+      t.string :payment_url
+
+      t.string :locale, null: false
+      t.references :form, null: false, foreign_key: true, index: false
+
+      t.timestamps null: false
+    end
+
+    add_index :form_translations, :locale, name: :index_form_translations_on_locale
+    add_index :form_translations, %i[form_id locale], name: :index_form_translations_on_form_id_and_locale, unique: true
+  end
+end

db/migrate/20251007151345_create_page_translations_for_mobility_table_backend.rb

@@ -0,0 +1,20 @@
+class CreatePageTranslationsForMobilityTableBackend < ActiveRecord::Migration[8.0]
+  def change
+    create_table :page_translations do |t|
+      # Translated attribute(s)
+      t.text :question_text
+      t.text :hint_text
+      t.jsonb :answer_settings
+      t.text :page_heading
+      t.text :guidance_markdown
+
+      t.string :locale, null: false
+      t.references :page, null: false, foreign_key: true, index: false
+
+      t.timestamps null: false
+    end
+
+    add_index :page_translations, :locale, name: :index_page_translations_on_locale
+    add_index :page_translations, %i[page_id locale], name: :index_page_translations_on_page_id_and_locale, unique: true
+  end
+end

db/migrate/20251007152124_create_condition_translations_for_mobility_table_backend.rb

@@ -0,0 +1,18 @@
+class CreateConditionTranslationsForMobilityTableBackend < ActiveRecord::Migration[8.0]
+  def change
+    create_table :condition_translations do |t|
+      # Translated attribute(s)
+      t.string :answer_value
+      t.text :exit_page_markdown
+      t.text :exit_page_heading
+
+      t.string :locale, null: false
+      t.references :condition, null: false, foreign_key: true, index: false
+
+      t.timestamps null: false
+    end
+
+    add_index :condition_translations, :locale, name: :index_condition_translations_on_locale
+    add_index :condition_translations, %i[condition_id locale], name: :index_condition_translations_on_condition_id_and_locale, unique: true
+  end
+end