class Cloudinary::Migrator

def start
  return if @started
  @started = true
  @terminate = false
  self.work.clear
  main = self
  Thread.abort_on_exception = true
  1.upto(@threads) do
    |i|
    Thread.start do
      while !main.terminate
        file = nil
        row = main.work.pop
        next if row.nil?
        begin
          debug "Thread #{i} - processing row #{row.inspect}. #{main.work.length} work waiting. #{main.results.length} results waiting."
          url = row["url"]
          cw = false
          result = nil
          if url.nil? && !self.retrieve.nil?
            data = self.retrieve.call(row["internal_id"])
            if defined?(ActiveRecord::Base) && data.is_a?(ActiveRecord::Base)
              cw = true
              data.save!
            elsif defined?(::CarrierWave) && defined?(Cloudinary::CarrierWave) && data.is_a?(Cloudinary::CarrierWave)
              cw = true
              begin
                data.model.save!
              rescue Cloudinary::CarrierWave::UploadError
                # upload errors will be handled by the result values.

              end
              result = data.metadata
            elsif data.respond_to?(:read) && data.respond_to?(:path)
              # This is an IO style object, pass as is.

              file = data
            elsif data.nil?
              # Skip

            elsif data.match(/^https?:/)
              url = data
            else
              file = main.temporary_file(data, row["public_id"] || "cloudinaryfile")
            end
          end
          if url || file
            options = main.extra_options.merge(:public_id=>row["public_id"])
            json_decode(row["metadata"]).each do
              |key, value|
              options[key.to_sym] = value
            end
            result = Cloudinary::Uploader.upload(url || file, options.merge(:return_error=>true)) || ({:error=>{:message=>"Received nil from uploader!"}})
          elsif cw
            result ||= {"status" => "saved"}
          else
            result = {"error" => {"message" => "Empty data and url", "http_code"=>404}}
          end
          main.results << {"id"=>row["id"], "internal_id"=>row["internal_id"], "result"=>result.to_json}
        rescue => e
          $stderr.print "Thread #{i} - Error in processing row #{row.inspect} - #{e}\n"
          debug(e.backtrace.join("\n"))
          sleep 1
        ensure
          main.mutex.synchronize{main.in_process -= 1}
          main.close_if_needed(file)
        end
      end
    end
  end
  retry_previous_queue # Retry all work from previous iteration before we start processing this one.

end