validation_form_builder.rb

class ValidationFormBuilder < ActionView::Helpers::FormBuilder
  include ActionView::Helpers::TagHelper
  include ActionView::Context  # 必須

  def validation_text_field(attribute, options = {})
    field_with_feedback(:text_field, attribute, options)
  end

  def validation_email_field(attribute, options = {})
    field_with_feedback(:email_field, attribute, options)
  end

  def validation_number_field(attribute, options = {})
    field_with_feedback(:number_field, attribute, options)
  end

  def validation_password_field(attribute, options = {})
    field_with_feedback(:password_field, attribute, options)
  end

  def validation_text_area(attribute, options = {})
    field_with_feedback(:text_area, attribute, options)
  end

  private

  def field_with_feedback(method, attribute, options)
    input_html = send("validatable_#{method}", attribute, options)
    feedback_html = error_feedback(attribute)
    safe_join([ input_html, feedback_html ])
  end

  def error_feedback(attribute)
    errors = object.errors[attribute]
    model_name = object_name # ← Rails FormBuilder が自動でセットするモデル名
    # 属性名を翻訳
    attribute_name = object.class.human_attribute_name(attribute)

    content_tag(:div, id: "#{model_name}_#{attribute}-feedback") do
      if errors.present?
        # エラーメッセージに属性名を追加
        formatted_errors = errors.map do |error|
          # エラーメッセージが既に属性名を含んでいる場合はそのまま使用
          if error.include?(attribute_name)
            error
          else
            "#{attribute_name}#{error}"
          end
        end
        content_tag(:span, formatted_errors.join(", "), class: "error")
      else
        "".html_safe
      end
    end
  end

  def validatable_text_field(attribute, options)
    options = add_validation_attributes(attribute, options)
    text_field(attribute, options)
  end

  # validatable_XXX のバリデーション属性を追加する処理（既に作っていたヘルパー相当）
  def validatable_email_field(attribute, options)
    options = add_validation_attributes(attribute, options)
    email_field(attribute, options)
  end

  def validatable_number_field(attribute, options)
    options = add_validation_attributes(attribute, options)
    number_field(attribute, options)
  end

  def validatable_password_field(attribute, options)
    options = add_validation_attributes(attribute, options)
    password_field(attribute, options)
  end

  def validatable_text_area(attribute, options)
    options = add_validation_attributes(attribute, options)
    text_area(attribute, options)
  end

  def add_validation_attributes(attribute, options)
    validators = object.class.validators_on(attribute)
    html = options.deep_dup
    model_name = object.class.model_name.human
    # 属性名を翻訳
    attribute_name = object.class.human_attribute_name(attribute)

    if validators.any? { |v| v.is_a?(ActiveModel::Validations::PresenceValidator) }
      html[:required] = true
      # エラーメッセージを手動で生成
      message = I18n.t("errors.messages.blank")
      html[:"data-message-required"] ||= "#{attribute_name}#{message}"
    end

    if validator = validators.find { |v| v.is_a?(ActiveModel::Validations::LengthValidator) }
      if validator.options[:minimum]
        html[:minlength] = validator.options[:minimum]
        # エラーメッセージを手動で生成
        message = I18n.t("errors.messages.too_short", count: validator.options[:minimum])
        html[:"data-message-too-short"] ||= "#{attribute_name}#{message}"
      end
    end

    if validator = validators.find { |v| v.is_a?(ActiveModel::Validations::NumericalityValidator) }
      if min = validator.options[:greater_than_or_equal_to]
        html[:min] = min
        # エラーメッセージを手動で生成
        message = I18n.t("errors.messages.greater_than_or_equal_to", count: min)
        html[:"data-message-range-underflow"] ||= "#{attribute_name}#{message}"
      end
      if max = validator.options[:less_than_or_equal_to]
        html[:max] = max
        # エラーメッセージを手動で生成
        message = I18n.t("errors.messages.less_than_or_equal_to", count: max)
        html[:"data-message-range-overflow"] ||= "#{attribute_name}#{message}"
      end
    end

    html
  end
end