das_download.rb

#! /usr/bin/env ruby
# usage:
# $ das_download.rb email password [download_directory]

require "mechanize"

class DasDownloader
  attr_reader :agent, :email, :password, :output_dir

  def initialize(email, password, output_dir)
    @agent = Mechanize.new
    @email, @password, @output_dir = email, password, output_dir
  end

  def screencasts
    seasons_html(catalog_html).each_with_index.map do |season_html,index|
      season = index + 1

      episodes_html(season_html).map do |episode_html|
        url = episode_html.at("a").attr("href")
        next unless (meta = episode_html.at(".row"))

        episode = meta.at(".number").text
        title = meta.at(".title").text
        download_url = scrape_download_url(url)

        Screencast.new season, episode, title, download_url
      end
    end.flatten
  end

  def scrape_download_url(url)
     raise "Unable to load details" unless (html = agent.get(url))

     # This is necessary because the video source url is set dynamically by javascript.
     return /resolution == \"1080p\"\) {\s*source\.src = \"(.*)\";/.match(html.at(".main_content").text)[1]
  end

  def run
    screencasts.each do |screencast|
      download screencast
    end
  end

  private

  def login
    agent.get "https://www.destroyallsoftware.com/screencasts/users/sign_in"

    if (form = agent.page.forms.first)
      form["user[email]"]    = email
      form["user[password]"] = password

      form.submit
      agent.pluggable_parser.default = Mechanize::Download
    end
  end

  def download(screencast)
    id = "S#{screencast.season.to_s.rjust(2, "0")}E#{screencast.episode.to_s.rjust(2, "0")}"
    title = screencast.title.gsub("/", "_").gsub(":", "").gsub(" ", "_").downcase
    filename = "Destroy.All.Software.#{id}.#{title}.mp4"
    puts "Downloading #{id} as #{filename}" 
    
    Dir.chdir(output_dir)
    return if File.exists? filename

    login
    agent.get(screencast.url).save(filename)
  end
  
  def catalog_html
    login

    agent.get "https://www.destroyallsoftware.com/screencasts/catalog"
    agent.page.search(".main_content")
  end

  def seasons_html(catalog)
    catalog.search(".season").reverse
  end

  def episodes_html(season)
    season.search(".episode")
  end

  Screencast = Struct.new(:season, :episode, :title, :url)
end

email    = ARGV[0] or raise("Please provide the email address for your account")
password = ARGV[1] or raise("Please provide the password for your account")
output_dir = ARGV[2] or raise("Please provide an output directory")

DasDownloader.new(email, password, output_dir).run