Fetch changelogs of updatable gems

changes.rb

require 'bundler'
require 'net/http'
require 'json'
require 'uri'

def fetch_gem(gem_name)
  URI("https://rubygems.org/api/v1/gems/#{gem_name}.json").
    then(&Net::HTTP.method(:get)).
    then(&JSON.method(:parse))
rescue JSON::ParserError
  {}
end

def fetch_changelog(gemspec)
  uri = gemspec.dig('metadata', 'changelog_uri')

  return unless uri

  URI(uri.sub('github.com', 'raw.githubusercontent.com').sub('/blob', '')).then(&Net::HTTP.method(:get))
end

def changelog_output(current_version, latest_version, changelog)
  return '' if changelog.nil?

  changelog.gsub /##? +v?#{current_version}.*/m, ''
end

Bundler.locked_gems.specs.map do |spec|
  name = spec.name
  version = spec.version.to_s
  gemspec = fetch_gem(name)
  latest_version = gemspec['version']

  if latest_version && version != latest_version
    changelog = fetch_changelog(gemspec)

    puts <<~OUT
      gem: #{name}
      Current version: #{version}
      Latest version:  #{latest_version}

      #{changelog_output(version, latest_version, changelog)}
    OUT
  end
end