record_identifier.rb

require 'active_support/core_ext/module'

module ActionController
  # The record identifier encapsulates a number of naming conventions for dealing with records, like Active Records or
  # Active Resources or pretty much any other model type that has an id. These patterns are then used to try elevate
  # the view actions to a higher logical level. Example:
  #
  #   # routes
  #   resources :posts
  #
  #   # view
  #   <%= div_for(post) do %>    <div id="post_45" class="post">
  #     <%= post.body %>           What a wonderful world!
  #   <% end %>                  </div>
  #
  #   # controller
  #   def update
  #     post = Post.find(params[:id])
  #     post.update_attributes(params[:post])
  #
  #     redirect_to(post) # Calls polymorphic_url(post) which in turn calls post_url(post)
  #   end
  #
  # As the example above shows, you can stop caring to a large extent what the actual id of the post is.
  # You just know that one is being assigned and that the subsequent calls in redirect_to expect that
  # same naming convention and allows you to write less code if you follow it.
  module RecordIdentifier
    extend self

    JOIN = '_'.freeze
    NEW = 'new'.freeze

    # The DOM class convention is to use the singular form of an object or class. Examples:
    #
    #   dom_class(post)   # => "post"
    #   dom_class(Person) # => "person"
    #
    # If you need to address multiple instances of the same class in the same view, you can prefix the dom_class:
    #
    #   dom_class(post, :edit)   # => "edit_post"
    #   dom_class(Person, :edit) # => "edit_person"
    def dom_class(record_or_class, prefix = nil)
      singular = ActiveModel::Naming.param_key(record_or_class)
      prefix ? "#{prefix}#{JOIN}#{singular}" : singular
    end

    # The DOM id convention is to use the singular form of an object or class with the id following an underscore.
    # If no id is found, prefix with "new_" instead. Examples:
    #
    #   dom_id(Post.find(45))       # => "post_45"
    #   dom_id(Post.new)            # => "new_post"
    #
    # If you need to address multiple instances of the same class in the same view, you can prefix the dom_id:
    #
    #   dom_id(Post.find(45), :edit) # => "edit_post_45"
    def dom_id(record, prefix = nil)
      if record_id = record_key_for_dom_id(record)
        "#{dom_class(record, prefix)}#{JOIN}#{record_id}"
      else
        dom_class(record, prefix || NEW)
      end
    end

  protected

    # Returns a string representation of the key attribute(s) that is suitable for use in an HTML DOM id.
    # This can be overwritten to customize the default generated string representation if desired.
    # If you need to read back a key from a dom_id in order to query for the underlying database record,
    # you should write a helper like 'person_record_from_dom_id' that will extract the key either based
    # on the default implementation (which just joins all key attributes with '_') or on your own
    # overwritten version of the method. By default, this implementation passes the key string through a
    # method that replaces all characters that are invalid inside DOM ids, with valid ones. You need to
    # make sure yourself that your dom ids are valid, in case you overwrite this method.
    def record_key_for_dom_id(record)
      record = record.to_model if record.respond_to?(:to_model)
      key = record.to_key
      key ? sanitize_dom_id(key.join('_')) : key
    end

    # Replaces characters that are invalid in HTML DOM ids with valid ones.
    def sanitize_dom_id(candidate_id)
      candidate_id # TODO implement conversion to valid DOM id values
    end
  end
end