class Mailings::HourlyThroughput
  HOUR = 1.hour
  RECENT = 15.minutes
  HISTORY_HOURS = 12

  def initialize(project, now: Time.current)
    @project = project
    @now = now
  end

  def sent
    @sent ||= sent_since(HOUR)
  end

  def recent_sent
    @recent_sent ||= sent_since(RECENT)
  end

  def failed
    @failed ||= recipients.failed.where(updated_at: (@now - HOUR)..@now).count
  end

  def drained
    sent + failed
  end

  def hourly_history
    @hourly_history ||= begin
      from = (@now - (HISTORY_HOURS - 1).hours).beginning_of_hour
      keyed = recipients.sent
        .where(sent_at: from..@now)
        .pluck(:sent_at)
        .each_with_object(Hash.new(0)) do |sent_at, counts|
          counts[sent_at.in_time_zone.beginning_of_hour] += 1
        end

      HISTORY_HOURS.times.map do |index|
        at = from + index.hours
        { at: at, count: keyed[at] || 0 }
      end
    end
  end

  def history_total
    hourly_history.sum { |bucket| bucket[:count] }
  end

  def history_max
    [hourly_history.map { |bucket| bucket[:count] }.max, 1].max
  end

  private

  def sent_since(window)
    recipients.sent.where(sent_at: (@now - window)..@now).count
  end

  def recipients
    MailingRecipient.joins(:mailing).merge(Mailing.for_project(@project))
  end
end