Get total video duration of a given topic from the Khan API.

README.md

Setup:

gem install httparty parallel

Usage: (get the ID from the topic page's URL; can be any level)

ruby khan_duration.rb solving-linear-equations-and-inequalities

khan_duration.rb

require 'ostruct'

require 'httparty'
require 'parallel'

class Khan
  include HTTParty
  base_uri 'www.khanacademy.org/api/v1'
  format :json

  def topic(topic_id)
    puts "Loading topic #{topic_id}"
    Topic.new(self.class.get("/topic/#{topic_id}"), self)
  end

  def video(video_id)
    puts "Loading video #{video_id}"
    Video.new(self.class.get("/videos/#{video_id}"))
  end

  class Video
    attr_reader :duration

    def initialize(api_data)
      @duration = api_data['duration']
    end
  end

  class Topic
    def initialize(api_data, khan)
      children_data_by_kind = api_data['children'].group_by { |c| c['kind'] }
      @topic_datas = children_data_by_kind['Topic'] || []
      @video_datas = children_data_by_kind['Video'] || []
      @khan = khan
    end

    def duration
      durables = subtopics + videos
      durables.map(&:duration).reduce(&:+)
    end

    def subtopics
      Parallel.map(@topic_datas, in_threads: 8) { |td| @khan.topic(td['id']) }
    end

    def videos
      Parallel.map(@video_datas, in_threads: 8) { |vd| @khan.video(vd['id']) }
    end
  end
end

topic_id = ARGV[0] || 'basic_addition'
khan = Khan.new
duration = khan.topic(topic_id).duration
puts "#{topic_id} lasts #{duration} seconds"