An attempt at rendering form fields in a generic way from a form representation as data.

generic_form_field_rendering.rb

require "scrivener"
require "hypertext"
require "hypertext/dsl"

class RegistrationForm < Scrivener
  attr_accessor :name
  attr_accessor :email
  attr_accessor :message

  def validate
    assert_present :name
    assert_present :email
    assert_present :message

    assert_email :email
  end

  def form
    {
      action: "/contact",
      method: "post",
      errors: errors,
      fields: attributes.keys.map do |attr|
        {
          "label" => {
            for: "#{attr}_field",
            text: attr.capitalize.to_s 
          },
          tag_mapping[attr] => {
            type: type_mapping[attr],
            name: attr,
            id: "#{attr}_field",
            value: send(attr),
            attribute: attr
          }.tap do |f|
            f[:text] = send(attr) if tag_mapping[attr] == "textarea"
          end
        }
      end.push({
        "input" => {
          type: :submit,
          value: "send"
        }
      })
    }
  end

  def tag_mapping
    {
      name: "input",
      email: "input",
      message: "textarea"
    }
  end

  def type_mapping
    {
      name: :text,
      email: :email,
    }
  end
end

class Template < Hypertext::DSL
  ATTRS = {
    "input" => %i(type name id value),
    "label" => %i(for),
    "textarea" => %i(id name rows cols)
  }

  def initialize(site)
    site.each_pair do |key, val|
      instance_variable_set(sprintf("@%s", key), val)
    end
    
    @ht = Hypertext.new
    render_form @form
  end
  
  def render(string)
    instance_eval string
  end
  
  def render_form(f)
    form f.slice(:action, :method) do
      f[:fields].each do |ff|
        render_field(ff)
      end
    end
  end

  def render_field(f)
    f.each do |tag, att|
      if att[:text]
        public_send tag, att.slice(*ATTRS.fetch(tag)) do
          text att[:text]
        end
      else
        public_send tag, att.slice(*ATTRS.fetch(tag))
      end
    end
  end
end

validator = RegistrationForm.new(message: "Hello, World!")
template = Template.new(form: validator.form)
puts template.to_s

# =>
# <form action="/contact" method="post">
#   <label for="email_field">
#     Email
#   </label>
#   <input type="email" name="email" id="email_field" value="" />
#   <label for="name_field">
#     Name
#   </label>
#   <input type="text" name="name" id="name_field" value="" />
#   <label for="message_field">
#     Message
#   </label>
#   <textarea id="message_field" name="message">
#     Hello, World!
#   </textarea>
#   <input type="submit" value="send" />
# </form>