Attach batch progress tracking to a model via concern

batch_job_stateful.rb

module BatchJobStateful
  extend ActiveSupport::Concern

  included do
    field :current_batch_id, type: String
    field :last_batch_total, type: Integer
    field :last_batch_failures, type: Integer
    field :last_batch_created_at, type: Time
    field :last_batch_completed_at, type: Time
  end

  def last_batch_duration
    (last_batch_completed_at || 0) - (last_batch_created_at || 0)
  end

  def last_batch_successful?
    (last_batch_total || 0) > 0 && last_batch_failures == 0
  end
  
  def processing?
    current_batch_status.present? && !current_batch_status.completed?
  end

  def progress
    return nil unless current_batch_status
    (current_batch_status.pending - current_batch_status.total).to_f / current_batch_status.total * 100
  end

  def estimated_completion(throughput_estimate_per_minute)
    return nil unless batch

    if progress < 0.25
      bad_estimated_completion(throughput_estimate_per_minute)
    else
      good_estimated_completion
    end
  end
  
  private

  def current_batch_status
    return @_current_batch_status if defined?(@_current_batch_status)
    @_current_batch_status = current_batch_id && Sidekiq::Batch::Status.new(current_batch_id)
  end

  def bad_estimated_completion(throughput_estimate_per_minute)
    now = Time.now

    remaining_time = (current_batch_status.total.to_f / throughput_estimate_per_minute).minutes
    estimate = current_batch_status.created_at + remaining_time

    if estimate > now
      estimate
    else
      now + remaining_time
    end
  end

  def good_estimated_completion
    now = Time.now

    elapsed_time = now - current_batch_status.created_at
    remaining_time = (100 - progress) * elapsed_time

    now + remaining_time
  end
end