transit_of_venus.rb

#!/usr/bin/env ruby -w
require 'open-uri'
require 'digest/md5'
require 'fileutils'

# this script creates a gif from NASA's high-res images of the sun
# the goal is to capture the transit of Venus in gif form
# it is expected that this will be run on OS X

# the following are required:
# [sudo] [brew|port] install imagemagick
# [sudo] [brew|port] install gifsicle

class TransitOfVenus
  
  URL = "http://sdo.gsfc.nasa.gov/assets/mov/depot/APOD/latest_APOD_HMIC_FR.jpg"
  OUT = File.join(ENV['HOME'], "Desktop", "venus")
  TMP = File.join(OUT, "tmp")
  
  class << self

    # where the magic happens
    def run!
      save_current_image
      convert_jpg_to_gif

      if they_are_different?
        combine_the_gifs
      else
        clean_up_the_duplicate_image
      end
    end

    def save_current_image
      puts "saving the current image"
      image_file = "#{Time.now.to_i}.jpg"

      FileUtils.mkdir_p(TMP)
      open(File.join(TMP, image_file), 'wb') do |local_file|
        local_file << open(URL).read
      end
    end

    def convert_jpg_to_gif
      puts "converting the jpg to a gif..."
      images = Dir.glob(File.join(TMP, "*.jpg")).sort

      images.each do |image| 
        filename = File.basename(image).split('.')[0]
        output = "#{filename}.gif"
        `convert #{File.expand_path(image)} #{File.join(TMP, output)}`
        puts "removing the original jpg"
        File.delete(File.expand_path(image))
      end
    end
    
    def they_are_different?
      puts "checking for differences"
      all_converted_images = Dir.glob(File.join(TMP, "*.gif")).sort

      return true if all_converted_images.count < 2
      penultimate, ultimate = all_converted_images[-2,2].map do |image| 
        Digest::MD5.hexdigest(File.read(image))
      end

      if penultimate == ultimate
        puts "current image is the same as previous image"
        return false
      else
        puts "new image found"
        return true
      end
    end

    def combine_the_gifs
      puts "making the final gif..."
      gifname = "#{Time.now.to_i}.gif"

      gifpath = File.join(OUT, gifname)
      `gifsicle --delay=10 --loop #{TMP}/*.gif > #{gifpath}`
      puts "saved final gif as #{gifpath}"
    end
    
    def clean_up_the_duplicate_image
      puts "removing the duplicate image"
      duplicate_image = Dir.glob(File.join(TMP, "*.gif")).last
      File.delete(duplicate_image)
    end
    
    def wait(minutes)
      minutes.downto(1).each do |n|
        s = n == 1 ? nil : "s"
        puts "sleeping for #{n} minute#{s}..."
        sleep 60
      end
    end
  end
end

if $0 == __FILE__
  loop do
    TransitOfVenus.run!
    TransitOfVenus.wait(10)
  end
end