# frozen_string_literal: true

require 'socket'

class PostScanner
  PORT_MAX = 65_536

  attr_reader :options, :opened

  def initialize(host, min, max = min, timeout = 1.0)
    abort "Max port number is #{PORT_MAX}" if max > PORT_MAX

    @options = {
      host: IPSocket.getaddress(host),
      min: min.to_i,
      max: max.to_i,
      timeout: timeout.to_f
    }
    @opened = []
    sockets
    puts "Port Size: #{sockets.size}"
    scan_ports
  end

  private

  def scan_ports
    loop do
      _, writable, = IO.select(nil, @sockets, nil, options.fetch(:timeout))
      break if writable.nil?

      writable.each do |socket|
        begin
          socket.connect_nonblock(socket.remote_address)
        rescue Errno::EISCONN
          port = socket.remote_address.ip_port
          @opened << port
          @sockets.delete(socket)
        rescue Errno::EINVAL, Errno::ENOTCONN => e
          @sockets.delete(socket)
        end
      end
    end
  end

  def sockets
    @sockets ||= begin
                   (options.fetch(:min)..options.fetch(:max)).map do |port|
                     begin
                       socket = Socket.new(:INET, :STREAM)
                       socket.setsockopt(:SOCKET, :REUSEADDR, true)
                       addr = Socket.sockaddr_in(port, options.fetch(:host))
                       socket.connect_nonblock(addr)
                     rescue Errno::EINPROGRESS
                       # nothing
                     end
                     socket
                   end
                 end
  end
end

Process.setrlimit(:NOFILE, PostScanner::PORT_MAX + 10)
scanner = PostScanner.new('github.com', 1, 20_000)
p scanner.opened.sort

IPSocket.getaddress(host)