Find transitive dependencies of a gem, sort by number of downloads

rdeps.rb

#! /usr/bin/env ruby
#
#  find transitive reverse dependencies of nokogiri with more than a million downloads: "rdeps.rb nokogiri 1000000"
#
require "bundler/inline"

gemfile do
  gem "json"
  gem "ruby-progressbar"
end

require "json"
require "open-uri"
require "ruby-progressbar"
require "set"

class ReverseDependencyCache
  CACHE_FILE = "ReverseDependency.cache"

  attr :name, :limit, :traversed

  def initialize(name, limit)
    @name = name
    @limit = limit
    @traversed = Set.new
  end

  def cache
    @cache ||= if File.exist?(CACHE_FILE)
                 JSON.parse(File.read(CACHE_FILE))
               else
                 {}
               end
  end
  
  def downloads(gem_name)
    cache[gem_name] ||= gem_info(gem_name)["downloads"]
  end

  def checkpoint
    FileUtils.cp(CACHE_FILE, "#{CACHE_FILE}.bak") if File.exist?(CACHE_FILE)
    File.open(CACHE_FILE, "w") { |f| f.write cache.to_json }
  end

  def populate_cache
    n_layer = 0
    layer = Set.new
    layer.merge(rdep_info(name))

    while !layer.empty?
      next_layer = Set.new
      
      pb = ProgressBar.create(total: layer.length,
                              title: "reverse dependency layer #{n_layer}",
                              format: "%c of %C in %t %B %e",
                              output: $stderr)

      layer.to_a.sort.each_with_index do |rdep, j|
        if downloads(rdep) >= limit
          next_layer = next_layer.merge(rdep_info(rdep)) - layer - traversed
          pb.log "... #{rdep} #{downloads(rdep)} (next layer will be #{next_layer.size})"
        end
        traversed.add(rdep)
        pb.increment
        checkpoint if j % 10 == 0
      end

      n_layer += 1
      layer = next_layer
    end
  end

  def report
    puts
    cache.find_all { |k,v| v >= limit && traversed.member?(k) }.sort_by { |k,v| -v }.each do |k,v|
      puts "#{k}: #{v}"
    end
  end

  private

  def gem_info(gem_name)
    JSON.parse(URI.open(sprintf("https://rubygems.org/api/v1/gems/%s.json", gem_name)).read)
  end

  def rdep_info(gem_name)
    JSON.parse(URI.open(sprintf("https://rubygems.org/api/v1/gems/%s/reverse_dependencies.json", gem_name)).read).uniq
  end
end

rdc = ReverseDependencyCache.new(ARGV[0], ARGV[1].to_i)
rdc.populate_cache
rdc.report