en:
  errors:
    format: '%{message}'

en:
  activemodel:
    errors:
      models:
        person:
          format: '%{message}'

en:
  activemodel:
    errors:
      models:
        person:
          attributes:
            name:
              format: '%{message}'

require "active_model"

module ActiveModel
  class Errors
    def full_message_i18n(attribute, message)
      return message if attribute == :base

      if @base.class.respond_to?(:i18n_scope)
        parts = attribute.to_s.split(".")
        attribute_name = parts.pop
        namespace = parts.join("/") unless parts.empty?
        attributes_scope = "#{@base.class.i18n_scope}.errors.models"

        if namespace
          defaults = @base.class.lookup_ancestors.map do |klass|
            [
              :"#{attributes_scope}.#{klass.model_name.i18n_key}/#{namespace}.attributes.#{attribute_name}.format",
              :"#{attributes_scope}.#{klass.model_name.i18n_key}/#{namespace}.format",
            ]
          end
        else
          defaults = @base.class.lookup_ancestors.map do |klass|
            [
              :"#{attributes_scope}.#{klass.model_name.i18n_key}.attributes.#{attribute_name}.format",
              :"#{attributes_scope}.#{klass.model_name.i18n_key}.format",
            ]
          end
        end

        defaults.flatten!
      else
        defaults = []
      end

      defaults << :"errors.format"
      defaults << "%{attribute} %{message}"

      attr_name = attribute.to_s.tr(".", "_").humanize
      attr_name = @base.class.human_attribute_name(attribute, default: attr_name)
      I18n.t(defaults.shift,
        default:  defaults,
        attribute: attr_name,
        message:   message)
    end
  end
end

class Person
  include ActiveModel::Validations
  extend  ActiveModel::Translation

  attr_accessor :title, :karma, :salary, :gender

  def condition_is_true
    true
  end

  def condition_is_false
    false
  end
end

person = Person.new

# Enumerate some representative scenarios here.
#
# It is very easy to make an optimization that improves performance for a
# specific scenario you care about but regresses on other common cases.
# Therefore, you should test your change against a list of representative
# scenarios. Ideally, they should be based on real-world scenarios extracted
# from production applications.
SCENARIOS = {
  "Deeply nested model attributes" => {
    attribute: :'contacts/addresses.street',
    translations: { errors: { format: "%{attribute} %{message}" } }
  },
  "Attribute with base format" => {
    attribute: :name,
    translations: { errors: { format: "%{attribute} %{message}" } }
  },
  "Attribute with attribute format" => {
    attribute: :name,
    translations: { activemodel: { errors: { models: { person: { attributes: { name: { format: "%{message}" } } } } } } }
  }
}

SCENARIOS.each_pair do |name, value|
  attribute = value[:attribute]
  translations = value[:translations]

  I18n.load_path.clear
  I18n.backend = I18n::Backend::Simple.new
  I18n.backend.store_translations("en", translations)

  puts
  puts " #{name} ".center(80, "=")
  puts

  Benchmark.ips do |x|
    x.report("full_message_i18n") { person.errors.full_message_i18n(attribute, "cannot be blank") }
    x.report("full_message") { person.errors.full_message(attribute, "cannot be blank") }
    x.compare!
  end
end

======================== Deeply nested model attributes ========================

Warming up --------------------------------------
   full_message_i18n     1.011k i/100ms
        full_message     1.423k i/100ms
Calculating -------------------------------------
   full_message_i18n     10.145k (± 3.9%) i/s -     51.561k in   5.090447s
        full_message     14.456k (± 3.9%) i/s -     72.573k in   5.028127s

Comparison:
        full_message:    14456.1 i/s
   full_message_i18n:    10144.8 i/s - 1.38x - 1.44x  slower


========================== Attribute with base format ==========================

Warming up --------------------------------------
   full_message_i18n     1.203k i/100ms
        full_message     1.834k i/100ms
Calculating -------------------------------------
   full_message_i18n     12.047k (± 4.0%) i/s -     60.150k in   5.000757s
        full_message     17.978k (± 1.9%) i/s -     89.866k in   5.000616s

Comparison:
        full_message:    17977.9 i/s
   full_message_i18n:    12047.3 i/s - 1.49x - 1.65x  slower


======================= Attribute with attribute format ========================

Warming up --------------------------------------
   full_message_i18n     1.553k i/100ms
        full_message     1.772k i/100ms
Calculating -------------------------------------
   full_message_i18n     16.465k (± 3.9%) i/s -     82.309k in   5.006884s
        full_message     17.041k (± 2.7%) i/s -     86.828k in   5.099021s

Comparison:
        full_message:    17040.9 i/s
   full_message_i18n:    16464.7 i/s - same-ish: difference falls within error to  1.20x  slower