shioyama/mobility

# frozen_string_literal: true
require "mobility/plugins/cache"

module Mobility
  module Backends
=begin

Stores attribute translation as rows on a model-specific translation table
(similar to Globalize[https://github.com/globalize/globalize]). By default,
the table name for a model +Post+ with table +posts+ will be
+post_translations+, and the translation class will be +Post::Translation+. The
translation class is dynamically created when the backend is initialized on the
model class, and subclasses
{Mobility::Backends::ActiveRecord::Table::Translation} (for AR models) or
inherits {Mobility::Backends::Sequel::Table::Translation} (for Sequel models).

The backend expects the translations table (+post_translations+) to have:

- a string column named +locale+ to store the locale of the translation
- columns for each translated attribute that uses the table (in general, this
  will be all attributes of the model)
- an integer column with name +post_id+ (where +post+ is the name of the model class)

If you are using Rails, you can use the +mobility:translations+ generator to
create a migration generating this table with:

  rails generate mobility:translations post title:string content:text

Unlike Globalize, attributes need not all be on one table. Mobility supports
any number of translation tables for a given model class (all of the structure
described above), provided the +association_name+ option is different for each.
Some translations can be stored on one translation table, others on
another, and Mobility will handle mapping reads/writes to each. The subclass
used in this case will be generated from the +association_name+ by
singularizing it and converting it to camelcase.

For more details, see examples in {Mobility::Backends::ActiveRecord::Table}.

==Backend Options

===+association_name+

Name of association on model. Defaults to +:translations+. If specified,
ensure name does not overlap with other methods on model or with the
association name used by other backends on model (otherwise one will overwrite
the other).

===+table_name+

Name of translations table. By default, if the table used by the model is
+posts+, the table name used for translations will be +post_translations+.

===+foreign_key+

Foreign key to use in defining the association on the model. By default, if the
model is a +Post+, this will be +post_id+. Generally this does not need to be
set.

===+subclass_name+

Subclass to use when dynamically generating translation class for model, by
default +:Translation+. Should be a symbol. Generally this does not need to be
set.

@see Mobility::Backends::ActiveRecord::Table
@see Mobility::Backends::Sequel::Table
=end
    module Table
      # @!method association_name
      #   Returns the name of the translations association.
      #   @return [Symbol] Name of the association

      # @!method subclass_name
      #   Returns translation subclass under model class namespace.
      #   @return [Symbol] Name of translation subclass

      # @!method foreign_key
      #   Returns foreign_key for translations association.
      #   @return [Symbol] Name of foreign key

      # @!method table_name
      #   Returns name of table where translations are stored.
      #   @return [Symbol] Name of translations table

      # @!group Backend Accessors
      # @!macro backend_reader
      def read(locale, **options)
        translation_for(locale, **options).send(attribute)
      end

      # @!macro backend_writer
      def write(locale, value, **options)
        translation_for(locale, **options).send("#{attribute}=", value)
      end
      # @!endgroup

      # @!macro backend_iterator
      def each_locale
        translations.each { |t| yield t.locale.to_sym }
      end

      private

      def translations
        model.send(association_name)
      end

      def self.included(backend_class)
        backend_class.extend ClassMethods
        backend_class.option_reader :association_name
        backend_class.option_reader :subclass_name
        backend_class.option_reader :foreign_key
        backend_class.option_reader :table_name
      end

      module ClassMethods
        def valid_keys
          [:association_name, :subclass_name, :foreign_key, :table_name]
        end

        # Apply custom processing for cache plugin
        def include_cache
          include self::Cache
        end

        def table_alias(locale)
          "#{table_name}_#{Mobility.normalize_locale(locale)}"
        end
      end

      # Simple hash cache to memoize translations as a hash so they can be
      # fetched quickly.
      module Cache
        def translation_for(locale, **options)
          return super(locale, options) if options.delete(:cache) == false
          if cache.has_key?(locale)
            cache[locale]
          else
            cache[locale] = super(locale, **options)
          end
        end

        def clear_cache
          cache.clear
        end

        private

        def cache
          if model.instance_variable_defined?(cache_name)
            model.instance_variable_get(cache_name)
          else
            model.instance_variable_set(cache_name, {})
          end
        end

        def cache_name
          @cache_name ||= :"@__mobility_#{association_name}_cache"
        end
      end
    end
  end
end