define_method かっこいい。

ext.rb

require 'garb'
require 'active_support/time'

class Visitor
  extend Garb::Model

  metrics :visitors, :percent_new_visits
end

module Reporter
  class << self
    %w(day week month).each do |period|
      define_method("between_a_#{period}") do |time|
        Garb::Session.login(ENV['ACCOUNT'], ENV['PASSWORD'])
        profile = Garb::Management::Profile.all.detect { |p| p.web_property_id == ENV['WPID'] }
        
        analytics = profile.visitor(
          start_date: time.send(:"beginning_of_#{period}"),
          end_date:   time.send(:"end_of_#{period}")
        )

        result = {}
        analytics.each do |r|
          result[:visitors] = r.visitors
          result[:percent_new_visits] = r.percent_new_visits
        end

        result
      end
    end
  end
end

Gemfile

source :rubygems

gem 'garb'
gem 'active_support'