application_controller.rb

def force_flush_cache
  CacheTumblrPost.update_cached_posts(true)
end

def runner_check_cache(force = false)
  cronlog_timestamp('start rebuild caches')	
  CacheTumblrPost.update_cached_posts(force)
  cronlog_timestamp('finish rebuild caches')
end

cache_builder.rake

namespace :remote_cache do
  
  desc "Rebuild the tumblr cache according to caching rules"
  task :check_tumblr => :environment do
    ApplicationController.new.runner_check_cache(false)
  end
  
  desc "Force Rebuild the tumblr cache"
  task :force_tumblr => :environment do
    ApplicationController.new.runner_check_cache(true)
  end
end

cache_tumblr_post.rb

class CacheTumblrPost < ActiveRecord::Base
  MAX_CACHE_LENGTH_IN_MINUTES = 300
  DEFAULT_AGE_IN_SECONDS = 10000000

  named_scope :completed, :conditions => 'incomplete != 1'

  class << self
    def login_and_get_tumblr_user(blog = nil)
      @tumblr_user ||= Tumblr::User.new('micahalbert@empoweringlives.org', 'sudan79')
      Tumblr.blog = blog || 'empoweringlives'
      @tumblr_user
    end

    def update_cached_posts(force = false)
      login_and_get_tumblr_user

      cronlog("cache age: #{CacheTumblrPost.age_in_minutes.round} minutes old")
      return false unless force || self.need_to_update?
      cronlog("build tumblr cache #{' - force_flush' if force}")

      posts = self.fetch_posts
      found_posts = 0
      good_posts = 0

      posts.each do |post|
        found_posts += 1
        next unless allow_to_add_post?(post)
        create!(
          :tumblr_post_id => post["id"],
          :title => post["regular_title"],
          :desc => post["regular_body"],
          :post_date => post["date"],
          :url => post["url_with_slug"],
          :reblog_key => post["reblog_key"],
          :post_type => post["type"],
          :incomplete => 1
        )
        good_posts += 1
      end

      if found_posts == total_count
        replace_by_new_cache!
        cronlog("Total Tumblr posts: #{found_posts} | Usable posts: #{good_posts}")
      elsif found_posts < total_count && found_posts > 1
        cronlog(
          "Error: Tumblr has #{total_count} posts but only #{found_posts} were retrieved"
        )
      else
        cronlog('Tumblr api/read Down --')
      end
    rescue
      cronlog('Tumblr posts fetching failed')
    end
  
    def allow_to_add_post?(post)
      post["type"] == "regular" && post['regular_title'] &&
        !self.exists?(:tumblr_post_id => post['id'], :incomplete => 1)
    end
  
    def total_count
      @total_count ||= Tumblr::Request.read["tumblr"]["posts"]["total"].to_i
    end

    def fetch_posts
      request_count = (total_count / 50) + 1
      posts = []

      request_count.times do |i|
        posts += Tumblr::Post.all(:query => { :start => 50 * i, :num => 50 }).uniq
      end
      posts
    rescue
      {}
    end

    def replace_by_new_cache!
      self.delete_all('incomplete != 1')
      self.update_all(:incomplete => 0)
    end

    def sample
      @sample ||= self.first(:conditions => "incomplete != 1")
    end

    def age_in_seconds
      if sample.present?
        Time.now -  sample.created_at.in_time_zone("Pacific Time (US & Canada)")
      else
        DEFAULT_AGE_IN_SECONDS
      end
    end

    def age_in_minutes
      age_in_seconds / 60
    end

    def need_to_update?
      sample.blank? || (age_in_minutes > MAX_CACHE_LENGTH_IN_MINUTES)
    end

    def cronlog(desc)
      puts DateTime.now.strftime("%y-%m-%d %H:%M:%S") + " - #{desc}"
    end
  end
end