# frozen_string_literal: true
module Steam
  module Networking
    # An object representing a packet from the connection.
    #
    # The packets come in the form
    #
    # LENGTH MAGIC BODY
    #
    # To create a packet only the body needs to be supplied. The body should
    # never contain the MAGIC or LENGTH
    class Packet
      # Valve's TCP Packet identifier
      TCP_MAGIC = 'VT01'

      # The raw bytes of the TCP packet
      attr_reader :body

      # The EMsg type derived from the Packet body
      attr_reader :msg_type
      alias emsg msg_type

      # Instantiates a Packet object
      #
      # @param body [String]
      def initialize(body)
        raise 'packet must have raw tcp body' if body.nil? || body.empty?

        @body     = body
        @io       = ByteReader.new(StringIO.new(body))
        @iden     = ByteReader.new(StringIO.new(body)).unsigned_int32
        @msg_type = @iden & ~Message::PROTO_MASK
        self
      end

      # Encode a Packet to a byte string
      #
      # @return [String] byte string representation of the Packet
      def encode
        stream = ByteWriter.new
        stream.write_unsigned_int32(body.length)
        stream.write(TCP_MAGIC)
        stream.write(body)
        stream.string
      end

      # Returns true if the Packet contains other packets
      #
      # @return [Bool]
      def multi?
        @msg_type == EMsg::MULTI
      end

      # Returns true if the Packet is Protobuf backed
      #
      # @return [Bool]
      def proto?
        (@iden & Message::PROTO_MASK) == Message::PROTO_MASK
      end

      # Converts the Packet into a Message object.
      #
      # @param msg [Message] The message to decode from the packet
      # @return [Message] the resulting message
      def as_message(msg)
        cm = if proto?
               ProtobufMessage.new(MsgHdrProtoBuf.new, msg, @msg_type)
             else
               ClientMessage.new(MsgHdr.new, msg, @msg_type)
             end

        cm.decode(@io)
        cm
      end
    end
  end
end