scopesessions.org/_plugins/image-reference-update.rb

require 'uri'
require 'faraday'
require 'yaml'
require 'mini_magick'

class Localizer

  IMAGE_FIELDS = ["media_artist_url"]
  RESIZED_SUFIX = "_resized.png"
  IMAGES_FOLDER = File.dirname(File.dirname(__FILE__))+'/images/'

  attr_reader :post_directory, :image_directory

  def initialize(post_directory, image_directory)
    @post_directory = post_directory
    @image_directory = image_directory
  end


  def localize_images
    Dir.foreach(@post_directory) do |file|
      next if !(file.end_with?('md') || file.end_with?('.markdown'))
      transform_file("#{@post_directory}#{File::SEPARATOR}#{file}")
    end
  end


  private


  def local_image_filename(url)
    uri = URI(url)
    "#{image_directory}#{File::SEPARATOR}#{File.basename(uri.path)}"
  end


  # downloads the file locally if it hasn't already been downloaded
  def ensure_local_image(url, local_file)
    return local_file if File.exist?(local_file)

    connection = Faraday.new do |faraday|
      faraday.adapter(Faraday.default_adapter)
    end
    response = download_file_helper(connection, url)
    File.open(local_file, 'wb') { |file| file << response.body }

    local_file
  end

  # helper to make sure that we can follow redirects, which can be important for
  # many of the cloud file sharing services out there.
  def download_file_helper(connection, url)
    response = connection.get do |req|
      req.url(url)
    end

    case response.status
    when 302
      download_file_helper(connection, response['Location'])
    when 200
      response
    else
      raise "Error downloading file: #{response.status}"
    end
  end


  def transform_file(file)
    puts "Transforming #{file}"
    contents = File.read(file, encoding: 'UTF-8')

    # Step 1: get all the images that must be downloaded
    yaml = YAML.load(contents)

    yaml['talks'].each do |talk|
     IMAGE_FIELDS.each do |image_field|

      image_url = talk[image_field]

      if !image_url.nil?

        # Download image if it is on the internet
        if image_url.start_with?('http') || image_url.start_with?('https')
          local_image = local_image_filename(image_url)

          begin
            ensure_local_image(image_url, local_image)
          rescue
            puts "Error downloading locally for image: #{image_url}"
            next
          end
        else
          puts "Skipping downloading of image: #{image_url}"
        end

        # Create resized version if it does not existZ
        if !(image_url.end_with? RESIZED_SUFIX)
          local_image = image_url + RESIZED_SUFIX
          resized_url = File.basename(image_url) + RESIZED_SUFIX
          image_path = IMAGES_FOLDER + File.basename(resized_url)
          if !File.file?(image_path)
            image_to_resize = MiniMagick::Image.open(IMAGES_FOLDER + File.basename(image_url))
            image_to_resize.resize('612x612')
            image_to_resize.format "png"
            image_to_resize.write(image_path)
            local_image = File.basename(resized_url)
          else
            puts "Skipping resizing of image: #{resized_url}"
          end
        end

        # Replace relative url on markdown file
        if !local_image.nil? && image_url != local_image
          contents = contents.gsub(image_url,local_image)
        end

      end

     end
    end

    puts(file)

    # Step 3: replace the file itself
    File.unlink(file)
    File.open(file, "w", encoding: "UTF-8") { |file| file.puts contents }

  end

end

localizer = Localizer.new('_posts', 'images')
localizer.localize_images