# rubocop:disable  Style/FrozenStringLiteralComment:
require 'net/ping/ping'

if File::ALT_SEPARATOR
  require 'win32/security'
end

# The Net module serves as a namespace only.
module Netchk
  # Modified version of Net::Ping::ICMP that does
  # not check for root privileges and uses a DGRAM
  # socket instead of a raw socket.
  class ICMP < ::Net::Ping
    ICMP_ECHOREPLY = 0 # Echo reply
    ICMP_ECHO      = 8 # Echo request
    ICMP_SUBCODE   = 0

    # You cannot set or change the port value. A value of 0 is always
    # used internally for ICMP pings.
    #
    undef_method :port=

    # Returns the data size, i.e. number of bytes sent on the ping. The
    # default size is 56.
    #
    attr_reader :data_size

    # Creates and returns a new Ping::ICMP object.  This is similar to its
    # superclass constructor, and the port value is ignored.
    def initialize(host = nil, port = nil, timeout = 5)
      @seq = 0
      @bind_port = 0
      @bind_host = nil
      @data_size = 56
      @data = ''

      0.upto(@data_size) { |n| @data << (n % 256).chr }

      @ping_id = (Thread.current.object_id ^ Process.pid) & 0xffff

      super(host, port, timeout)
      @port = nil # This value is not used in ICMP pings.
    end

    # Sets the number of bytes sent in the ping method.
    #
    def data_size=(size)
      @data_size = size
      @data = ''
      0.upto(size) { |n| @data << (n % 256).chr }
    end

    # Associates the local end of the socket connection with the given
    # +host+ and +port+. The default port is 0.
    #
    def bind(host, port = 0)
      @bind_host = host
      @bind_port = port
    end

    # Pings the +host+ specified in this method or in the constructor.  If a
    # host was not specified either here or in the constructor, an
    # ArgumentError is raised.
    #
    def ping(host = @host)
      super(host)
      bool = false

      socket = Socket.new(
        Socket::PF_INET,
        Socket::SOCK_DGRAM,
        Socket::IPPROTO_ICMP
      )

      if @bind_host
        saddr = Socket.pack_sockaddr_in(@bind_port, @bind_host)
        socket.bind(saddr)
      end

      @seq = (@seq + 1) % 65536
      pstring = 'C2 n3 A' << @data_size.to_s
      timeout = @timeout

      checksum = 0
      msg = [ICMP_ECHO, ICMP_SUBCODE, checksum, @ping_id, @seq, @data].pack(pstring)

      checksum = checksum(msg)
      msg = [ICMP_ECHO, ICMP_SUBCODE, checksum, @ping_id, @seq, @data].pack(pstring)

      begin
        saddr = Socket.pack_sockaddr_in(0, host)
      rescue Exception
        socket.close unless socket.closed?
        return bool
      end

      start_time = Time.now

      socket.send(msg, 0, saddr) # Send the message

      begin
        Timeout.timeout(@timeout) {
          while true
            io_array = select([socket], nil, nil, timeout)

            if io_array.nil? || io_array[0].empty?
              raise Timeout::Error if io_array.nil?
              return false
            end

            ping_id = nil
            seq = nil

            data = socket.recvfrom(1500).first
            type = data[20, 2].unpack('C2').first

            case type
            when ICMP_ECHOREPLY
              if data.length >= 28
                ping_id, seq = data[24, 4].unpack('n3')
              end
            else
              if data.length > 56
                ping_id, seq = data[52, 4].unpack('n3')
              end
            end

            if ping_id == @ping_id && seq == @seq && type == ICMP_ECHOREPLY
              bool = true
              break
            end
          end
        }
      rescue Exception => err
        @exception = err
      ensure
        socket.close if socket
      end

      # There is no duration if the ping failed
      @duration = Time.now - start_time if bool
    end

    private

      # Perform a checksum on the message.  This is the sum of all the short
      # words and it folds the high order bits into the low order bits.
      #
      def checksum(msg)
        length    = msg.length
        num_short = length / 2
        check     = 0

        msg.unpack("n#{num_short}").each do |short|
          check += short
        end

        if length % 2 > 0
          check += msg[length - 1, 1].unpack('C').first << 8
        end

        check = (check >> 16) + (check & 0xffff)
        return (~((check >> 16) + check) & 0xffff)
      end
  end
end