Docker stats with image name

docker-stats.rb

#!/usr/bin/env ruby
require 'open3'

class String
  def truncate(max, omission: '')
    length > max ? "#{self[0...max - omission.length]}#{omission}" : self
  end
end

COLUMN_WIDTH = 30
id2name = {}
header = 'IMAGE NAME'.ljust(COLUMN_WIDTH).freeze
Thread.new do
  while true
    _, stdout = Open3.popen2('docker ps --format "{{.ID}}\t{{.Image}}"')
    stdout.each_line do |line|
      container_id, image_name = line.chomp.split("\t")
      id2name[container_id] = image_name
    end
    sleep 0.5
  end
end

Open3.popen3('docker stats') do |stdin, stdout, stderr, wait_thr|
  stdout.each_line do |line|
    matched = line.to_s.match(/^(?<container_id>[a-z0-9]+)\s+/)
    if matched
      container_id = matched[:container_id]
      image_name = id2name[container_id] || "Not Found"
      optimized_image_name = image_name.truncate(COLUMN_WIDTH - 1, omission: '...').ljust(COLUMN_WIDTH)

      puts "#{optimized_image_name}#{line}"
    else
      line.gsub!('CONTAINER ID', "#{header}CONTAINER ID")
      puts line
    end
  end
end