module IdentityCache
  module CacheKeyGeneration
    extend ActiveSupport::Concern

    module ClassMethods
      def rails_cache_key(id)
        rails_cache_key_prefix + id.to_s
      end

      def rails_cache_key_prefix
        @rails_cache_key_prefix ||= begin
          "IDC:blob:#{base_class.name}:#{IdentityCache.denormalized_schema_hash(self)}:"
        end
      end

      def rails_cache_index_key_for_fields_and_values(fields, values)
        "IDC:index:#{base_class.name}:#{rails_cache_string_for_fields_and_values(fields, values)}"
      end

      def rails_cache_key_for_attribute_and_fields_and_values(attribute, fields, values)
        "IDC:attribute:#{base_class.name}:#{attribute}:#{rails_cache_string_for_fields_and_values(fields, values)}"
      end

      def rails_cache_string_for_fields_and_values(fields, values)
        "#{fields.join('/')}:#{IdentityCache.memcache_hash(values.join('/'))}"
      end
    end

    def primary_cache_index_key # :nodoc:
      self.class.rails_cache_key(id)
    end

    def secondary_cache_index_key_for_current_values(fields) # :nodoc:
      self.class.rails_cache_index_key_for_fields_and_values(fields, fields.collect {|field| self.send(field)})
    end

    def secondary_cache_index_key_for_previous_values(fields) # :nodoc:
      self.class.rails_cache_index_key_for_fields_and_values(fields, old_values_for_fields(fields))
    end

    def attribute_cache_key_for_attribute_and_previous_values(attribute, fields) # :nodoc:
      self.class.rails_cache_key_for_attribute_and_fields_and_values(attribute, fields, old_values_for_fields(fields))
    end

    def old_values_for_fields(fields) # :nodoc:
      fields.map do |field|
        field_string = field.to_s
        if destroyed? && transaction_changed_attributes.has_key?(field_string)
          transaction_changed_attributes[field_string]
        elsif persisted? && transaction_changed_attributes.has_key?(field_string)
          transaction_changed_attributes[field_string]
        else
          self.send(field)
        end
      end
    end
  end
end