-

class SVPProto(object):
    @staticmethod
    def size_of_package(ctx):
        print ctx
        return 1

    REQUEST = construct.Struct("SVPRequest",
        construct.ULInt16("version"),
        construct.ULInt16("serial"),
        construct.Value(construct.ULInt16("size"), size_of_package),
        construct.ULInt32("_reserved"),
        construct.ULInt64("imei"),
        construct.GreedyRange(
            construct.Subconstruct(construct.Struct("Content",
                construct.Enum(
                    construct.ULInt8("type"),
                    position1="\x01",
                    position2="\x02",
                    _default_="\x01"
                ),
                construct.Switch("content", lambda ctx: ctx.type, {
                    "\x01": construct.Subconstruct(construct.Struct("Position",
                        construct.Const(construct.ULInt8("size"), 19),
                        construct.Enum(construct.ULInt8("is_valid"), valid=1, invalid=0, _default_=1),
                        construct.Value(construct.ULInt32("ts"), lambda ctx: int(time())),
                        construct.LFloat32("lat"),
                        construct.LFloat32("lon"),
                        construct.SLInt16("alt"),
                        construct.ULInt8("speed"),
                        CourseAdapter(construct.ULInt8("course")),
                        construct.ULInt8("satellites"),
                    )),
                    "\x02": construct.Subconstruct(construct.Struct("Position2",
                        construct.Const(construct.ULInt8("size"), 16),
                        construct.ULInt8("precision"),
                        construct.ULInt32("ts"),
                        construct.LFloat32("lat"),
                        construct.LFloat32("lon"),
                        construct.Bytes("_reserved", 3)
                    )),
                    "\xff": construct.Subconstruct(construct.Struct("SignatureContainer",
                        construct.Value("size", lambda ctx: ctx['']),
                        construct.Bytes("Signature", 255)
                    ))
                })
            ))
        )
    )

    RESPONSE = construct.Struct("SVPResponse",
        construct.Byte("type"),
        construct.Byte("size"),
        construct.Byte("cmd"),
        construct.Bytes("args", 4),
    )