download all comments of a youtube video

script.rb

#!/usr/bin/env ruby

# usage: script.rb <video_id> <api_key>

require 'json'
require 'net/http'

video_id = ARGV[0].tap { |s| s&.length&.<(13) || fail('pass video id as first argument') }
key      = ARGV[1].tap { |s| s&.length&.>(13) || fail('pass api key as second argument') }
url      = "https://youtube.googleapis.com/youtube/v3/commentThreads?part=snippet&videoId=#{video_id}&key=#{key}"
items    = []

Net::HTTP.start(URI.parse(url).host, use_ssl: true) do |http|
  loop do
    puts "downloading comments page #{@next_page_token}"
    response = http.get("#{url}#{@next_page_token && "&pageToken=#{@next_page_token}"}")
    response.code.to_i == 200 || fail("#{response.code}: #{response.body}")
    data = JSON(response.body)
    items += data['items']
    break if data['items'].none? || (@next_page_token = data['nextPageToken']).to_s.empty?
  end
end

File.write("#{video_id}_comments.json", items.to_json)