module that enables a model to produce "time ago" string representations for any given date field (requires active_support)

make_time_agoable.rb

module MakeTimeAgoable
  extend ActiveSupport::Concern

  included do
    # code goes here that should be run on the actual include
    # or just leave it blank. no one cares. where's my cake?
  end

  module ClassMethods
    attr_reader :_time_agoable

    # Usage:
    #
    #   For a model that has date fields (ex. created_at, updated_at, etc.) and
    #   that includes this module, you can call make_time_agoable, passing in
    #   +*date_fields+ as a list that you'd like to be made "time ago"-able.
    #
    #   "time-ago"-able means we can get a value of how long ago the given date
    #   was in a nice, friendly format.
    #
    #   For example, if created_at was set to a timestamp that was 3 days
    #   ago, by using make_time_agoable we could get the output of "3 days ago"
    #
    #   Let's look at an example:
    #
    #     class Lolrus
    #       make_time_agoable :created_at, :updated_at
    #     end
    #
    #   Now we'll have the following methods metaprogrammed for us:
    #
    #     Lolrus#created_at_time_ago (tied to the Lolrus instance's created_at field)
    #     Lolrus#updated_at_time_ago (tied to the Lolrus instance's updated_at field)
    #
    #   Each method will return the equivalent of using the Rails
    #   distance_of_time_in_words_to_now helper if passed the field it is tied
    #   to (we append "ago" for convenience, but you get the point):
    #
    #     a_lolrus = Lolrus.new(:created_at => Time.now)
    #
    #     [sudo code]
    #     (distance_of_time_in_words_to_now(a_lolrus.created_at) + " ago") == a_lolrus.created_at_time_ago
    #
    #   With this module, we can get these timeframe representations back from the model,
    #   rather than depending on the view helper.
    #
    #   A usecase is when dealing with an app that leverages client-side UI rendering / updating
    #   by hitting an api backend using js, for example. Although we can't use server-side view helpers,
    #   we can now get nicely formated timeframes from the model. Hooray.
    #
    #   Alternatively we could write the equivalent helper in js and modify the
    #   data that way.
    def make_time_agoable(*date_fields)
      # create hash of form {method name => underlying field} for passed date fields
      @_time_agoable = date_fields.reduce({}) do |agg, fld|
        agg["#{fld}_time_ago".to_sym] = fld.to_sym
        agg
      end

      # dynamically define methods
      @_time_agoable.each do |method_name, underlying_field|
        define_method method_name do
          "#{distance_of_time_in_words(read_attribute(underlying_field), Time.now)} ago"
        end
      end

      # add default as_json that includes these newly generated methods so
      # they'll be included in any #to_json requests. This can be overriden in
      # the model if needed. Just remember to include the dynamically generated
      # methods if you do!
      define_method :as_json do |options|
        super methods: self.class._time_agoable.keys
      end
    end
  end

private

  # pulled from Rails 2.1 (pre-internationalization)
  # TODO: use current, I18n-leveraging version, es mas bueno
  def distance_of_time_in_words(from_time, to_time = 0, include_seconds = false)
    from_time = from_time.to_time if from_time.respond_to?(:to_time)
    to_time = to_time.to_time if to_time.respond_to?(:to_time)
    distance_in_minutes = (((to_time - from_time).abs)/60).round
    distance_in_seconds = ((to_time - from_time).abs).round

    case distance_in_minutes
      when 0..1
        return (distance_in_minutes == 0) ? 'less than a minute' : '1 minute' unless include_seconds
        case distance_in_seconds
          when 0..4   then 'less than 5 seconds'
          when 5..9   then 'less than 10 seconds'
          when 10..19 then 'less than 20 seconds'
          when 20..39 then 'half a minute'
          when 40..59 then 'less than a minute'
          else             '1 minute'
        end

      when 2..44           then "#{distance_in_minutes} minutes"
      when 45..89          then 'about 1 hour'
      when 90..1439        then "about #{(distance_in_minutes.to_f / 60.0).round} hours"
      when 1440..2879      then '1 day'
      when 2880..43199     then "#{(distance_in_minutes / 1440).round} days"
      when 43200..86399    then 'about 1 month'
      when 86400..525599   then "#{(distance_in_minutes / 43200).round} months"
      when 525600..1051199 then 'about 1 year'
      else                      "over #{(distance_in_minutes / 525600).round} years"
    end
  end
end