gen-msteams-new

#!/usr/bin/env ruby

require 'json'
require 'open-uri'
require 'securerandom'
require 'ipaddr'

 # Any GUID is okay, but splitting them to separate use cases.
PULL_GUID = 'f11f029f-a2d4-4b75-92cd-2df8a9549b65'
DESC_GUID = 'b794baa0-662f-4592-b4f0-46ab3284b612'
PROCESS = '/Applications/Microsoft Teams.app/Contents/MacOS/MSTeams'

def endpoint(guid = SecureRandom.uuid)
  'https://endpoints.office.com/endpoints/worldwide' \
  "?clientrequestid=#{guid}&ServiceAreas=Skype"
end

def ports_to_ranges(ports)
  ports
    .split(',')
    .map(&:to_i)
    .chunk_while { |a, b| a.succ == b }
    .map { |h, *t| [h, t.last].compact.join('-') }
    .join(',')
end

def ips_to_ranges(ip_strings)
  ip_strings
    .map { |ip_string|
      ip_range = IPAddr.new(ip_string).to_range
      a = ip_range.begin.to_s
      b = ip_range.end.to_s
      a == b ? a : "#{a}-#{b}"
    }
    .join(',')
end

def get_domains(urls)
  urls
    .select { |v| v.start_with?('*') }
    .map { |d| d.start_with?('*.') ? d[2..-1] : d[1..-1] }
end

def get_hosts(urls, domains = get_domains(urls))
  urls.reject { |v| v.start_with?('*') } - domains
end

msrules = JSON.parse(URI.open(endpoint(PULL_GUID)).read)

def extract_lsrules(msrule)
  lsrule = {
    'action'  => 'allow',
    'notes'   => msrule['notes'],
    'process' => PROCESS
  }.compact

  lsrules = []

  %w[ips hosts domains].product(%w[tcp udp]).each do |dest_type, protocol|
    case dest_type
    when 'ips'
      next unless ['ips', "#{protocol}Ports"].all? { |k| msrule.key?(k) }

      lsrules << lsrule.merge(
        'remote-addresses' => ips_to_ranges(msrule['ips']),
        'ports'            => ports_to_ranges(msrule["#{protocol}Ports"]),
        'protocol'         => protocol
      )
    when 'hosts'
      next unless ['urls', "#{protocol}Ports"].all? { |k| msrule.key?(k) }
      hosts = get_hosts(msrule['urls'])
      next if hosts.none?

      lsrules << lsrule.merge(
        'remote-hosts'   => hosts,
        'ports'          => ports_to_ranges(msrule["#{protocol}Ports"]),
        'protocol'       => protocol
      )
    when 'domains'
      next unless ['urls', "#{protocol}Ports"].all? { |k| msrule.key?(k) }
      domains = get_domains(msrule['urls'])
      next if domains.none?

      lsrules << lsrule.merge(
        'remote-domains' => domains,
        'ports'          => ports_to_ranges(msrule["#{protocol}Ports"]),
        'protocol'       => protocol
      )
    end
  end

  lsrules
end

puts JSON.pretty_generate \
  description: "Rules based on Microsoft Endpoints at #{endpoint(DESC_GUID)}",
  name:        'Microsoft Teams',
  rules:       msrules.flat_map { |msrule| extract_lsrules(msrule) }