analyzer.rb

class Analyzer
  class << self
    include ActionView::Helpers::NumberHelper
  end

  CACHE_NAMESPACE = "analyzer"
  CACHE_LIFESPAN = 10.minutes

  class_attribute :items_to_analyze

  def self.analyze(name, &block)
    (self.items_to_analyze ||= []) << Item.new(name_prefix, name, block)
  end

  def initialize(collection, options={})
    @collection = collection
    @options = options
  end

  def results
    @results ||= Rails.cache.fetch(cache_key, expires_in: CACHE_LIFESPAN) do
      items_to_analyze.map { |i| i.call_to_hash(@collection, @options) }
    end
  end

  def cached?
    Rails.cache.exist?(cache_key)
  end

  private

  def self.name_prefix
    self.name.underscore.gsub("_analyzer", "")
  end

  def self.format_number(num)
    number_with_delimiter(num)
  end

  def self.format_money(cents)
    "$#{format_number(Money.new(cents))}"
  end

  def self.format_percentage(decimal)
    "#{format_number((decimal*100).to_i)}%"
  end

  def collection_identifier
    @collection_identifier ||=
      Digest::MD5.hexdigest(coerced_collection.to_sql + @options.to_json)
  end

  def coerced_collection
    @coerced_collection ||= if @collection.is_a?(ActiveRecord::Relation)
      @collection
    else
      @collection.where("")
    end
  end

  def cache_key
    "#{CACHE_NAMESPACE}:#{collection_identifier}"
  end

end