"""
Extremely minimal streaming codec for a subset of protobuf.  Supports uint32,
bytes, string, embedded message and repeated fields.
"""

if False:
    from typing import Any, Dict, Iterable, List, Tuple, Type, TypeVar, Union
    from typing_extensions import Protocol

    class Reader(Protocol):
        def readinto(self, buf: bytearray) -> int:
            """
            Reads `len(buf)` bytes into `buf`, or raises `EOFError`.
            """

    class Writer(Protocol):
        def write(self, buf: bytes) -> int:
            """
            Writes all bytes from `buf`, or raises `EOFError`.
            """


_UVARINT_BUFFER = bytearray(1)


def load_uvarint(reader: Reader) -> int:
    buffer = _UVARINT_BUFFER
    result = 0
    shift = 0
    byte = 0x80
    while byte & 0x80:
        reader.readinto(buffer)
        byte = buffer[0]
        result += (byte & 0x7F) << shift
        shift += 7
    return result


def dump_uvarint(writer: Writer, n: int) -> None:
    if n < 0:
        raise ValueError("Cannot dump signed value, convert it to unsigned first.")
    buffer = _UVARINT_BUFFER
    shifted = 1
    while shifted:
        shifted = n >> 7
        buffer[0] = (n & 0x7F) | (0x80 if shifted else 0x00)
        writer.write(buffer)
        n = shifted


def count_uvarint(n: int) -> int:
    if n < 0:
        raise ValueError("Cannot dump signed value, convert it to unsigned first.")
    if n <= 0x7F:
        return 1
    if n <= 0x3FFF:
        return 2
    if n <= 0x1F_FFFF:
        return 3
    if n <= 0xFFF_FFFF:
        return 4
    if n <= 0x7_FFFF_FFFF:
        return 5
    if n <= 0x3FF_FFFF_FFFF:
        return 6
    if n <= 0x1_FFFF_FFFF_FFFF:
        return 7
    if n <= 0xFF_FFFF_FFFF_FFFF:
        return 8
    if n <= 0x7FFF_FFFF_FFFF_FFFF:
        return 9
    raise ValueError


# protobuf interleaved signed encoding:
# https://developers.google.com/protocol-buffers/docs/encoding#structure
# the idea is to save the sign in LSbit instead of twos-complement.
# so counting up, you go: 0, -1, 1, -2, 2, ... (as the first bit changes, sign flips)
#
# To achieve this with a twos-complement number:
# 1. shift left by 1, leaving LSbit free
# 2. if the number is negative, do bitwise negation.
#    This keeps positive number the same, and converts negative from twos-complement
#    to the appropriate value, while setting the sign bit.
#
# The original algorithm makes use of the fact that arithmetic (signed) shift
# keeps the sign bits, so for a n-bit number, (x >> n) gets us "all sign bits".
# Then you can take "number XOR all-sign-bits", which is XOR 0 (identity) for positive
# and XOR 1 (bitwise negation) for negative. Cute and efficient.
#
# But this is harder in Python because we don't natively know the bit size of the number.
# So we have to branch on whether the number is negative.


def sint_to_uint(sint: int) -> int:
    res = sint << 1
    if sint < 0:
        res = ~res
    return res


def uint_to_sint(uint: int) -> int:
    sign = uint & 1
    res = uint >> 1
    if sign:
        res = ~res
    return res


class UVarintType:
    WIRE_TYPE = 0


class SVarintType:
    WIRE_TYPE = 0


class BoolType:
    WIRE_TYPE = 0


class EnumType:
    WIRE_TYPE = 0

    def __init__(self, name: str, enum_values: Iterable[int]) -> None:
        self.enum_values = enum_values

    def validate(self, fvalue: int) -> int:
        if fvalue in self.enum_values:
            return fvalue
        else:
            raise TypeError("Invalid enum value")


class BytesType:
    WIRE_TYPE = 2


class UnicodeType:
    WIRE_TYPE = 2


class MessageType:
    WIRE_TYPE = 2
    UNSTABLE = False

    # Type id for the wire codec.
    # Technically, not every protobuf message has this.
    MESSAGE_WIRE_TYPE = -1

    @classmethod
    def get_fields(cls) -> "FieldDict":
        return {}

    def __eq__(self, rhs: Any) -> bool:
        return self.__class__ is rhs.__class__ and self.__dict__ == rhs.__dict__

    def __repr__(self) -> str:
        return "<%s>" % self.__class__.__name__


class LimitedReader:
    def __init__(self, reader: Reader, limit: int) -> None:
        self.reader = reader
        self.limit = limit

    def readinto(self, buf: bytearray) -> int:
        if self.limit < len(buf):
            raise EOFError
        else:
            nread = self.reader.readinto(buf)
            self.limit -= nread
            return nread


FLAG_REPEATED = object()
FLAG_REQUIRED = object()
FLAG_EXPERIMENTAL = object()

if False:
    MessageTypeDef = Union[
        Type[UVarintType],
        Type[SVarintType],
        Type[BoolType],
        EnumType,
        Type[BytesType],
        Type[UnicodeType],
        Type[MessageType],
    ]
    FieldDef = Tuple[str, MessageTypeDef, Any]
    FieldDict = Dict[int, FieldDef]

    FieldCache = Dict[Type[MessageType], FieldDict]

    LoadedMessageType = TypeVar("LoadedMessageType", bound=MessageType)


def load_message(
    reader: Reader,
    msg_type: Type[LoadedMessageType],
    field_cache: FieldCache = None,
    experimental_enabled: bool = True,
) -> LoadedMessageType:
    if field_cache is None:
        field_cache = {}
    fields = field_cache.get(msg_type)
    if fields is None:
        fields = msg_type.get_fields()
        field_cache[msg_type] = fields

    if msg_type.UNSTABLE and not experimental_enabled:
        raise ValueError  # experimental messages not enabled

    # we need to avoid calling __init__, which enforces required arguments
    msg: LoadedMessageType = object.__new__(msg_type)
    # pre-seed the object with defaults
    for fname, _, fdefault in fields.values():
        if fdefault is FLAG_REPEATED:
            fdefault = []
        elif fdefault is FLAG_EXPERIMENTAL:
            fdefault = None
        setattr(msg, fname, fdefault)

    if False:
        SingularValue = Union[int, bool, bytearray, str, MessageType]
        Value = Union[SingularValue, List[SingularValue]]
        fvalue: Value = 0

    while True:
        try:
            fkey = load_uvarint(reader)
        except EOFError:
            break  # no more fields to load

        ftag = fkey >> 3
        wtype = fkey & 7

        field = fields.get(ftag, None)

        if field is None:  # unknown field, skip it
            if wtype == 0:
                load_uvarint(reader)
            elif wtype == 2:
                ivalue = load_uvarint(reader)
                reader.readinto(bytearray(ivalue))
            else:
                raise ValueError
            continue

        fname, ftype, fdefault = field
        if wtype != ftype.WIRE_TYPE:
            raise TypeError  # parsed wire type differs from the schema

        if fdefault is FLAG_EXPERIMENTAL and not experimental_enabled:
            raise ValueError  # experimental fields not enabled

        ivalue = load_uvarint(reader)

        if ftype is UVarintType:
            fvalue = ivalue
        elif ftype is SVarintType:
            fvalue = uint_to_sint(ivalue)
        elif ftype is BoolType:
            fvalue = bool(ivalue)
        elif isinstance(ftype, EnumType):
            fvalue = ftype.validate(ivalue)
        elif ftype is BytesType:
            fvalue = bytearray(ivalue)
            reader.readinto(fvalue)
        elif ftype is UnicodeType:
            fvalue = bytearray(ivalue)
            reader.readinto(fvalue)
            fvalue = bytes(fvalue).decode()
        elif issubclass(ftype, MessageType):
            fvalue = load_message(
                LimitedReader(reader, ivalue), ftype, field_cache, experimental_enabled
            )
        else:
            raise TypeError  # field type is unknown

        if fdefault is FLAG_REPEATED:
            getattr(msg, fname).append(fvalue)
        else:
            setattr(msg, fname, fvalue)

    for fname, _, _ in fields.values():
        if getattr(msg, fname) is FLAG_REQUIRED:
            # The message is intended to be user-facing when decoding from wire,
            # but not when used internally.
            raise ValueError("Required field '{}' was not received".format(fname))

    return msg


def dump_message(
    writer: Writer, msg: MessageType, field_cache: FieldCache = None
) -> None:
    repvalue = [0]

    if field_cache is None:
        field_cache = {}
    fields = field_cache.get(type(msg))
    if fields is None:
        fields = msg.get_fields()
        field_cache[type(msg)] = fields

    for ftag in fields:
        fname, ftype, fdefault = fields[ftag]

        fvalue = getattr(msg, fname, None)
        if fvalue is None:
            continue

        fkey = (ftag << 3) | ftype.WIRE_TYPE

        if fdefault is not FLAG_REPEATED:
            repvalue[0] = fvalue
            fvalue = repvalue

        for svalue in fvalue:
            dump_uvarint(writer, fkey)

            if ftype is UVarintType:
                dump_uvarint(writer, svalue)

            elif ftype is SVarintType:
                dump_uvarint(writer, sint_to_uint(svalue))

            elif ftype is BoolType:
                dump_uvarint(writer, int(svalue))

            elif isinstance(ftype, EnumType):
                dump_uvarint(writer, svalue)

            elif ftype is BytesType:
                if isinstance(svalue, list):
                    dump_uvarint(writer, _count_bytes_list(svalue))
                    for sub_svalue in svalue:
                        writer.write(sub_svalue)
                else:
                    dump_uvarint(writer, len(svalue))
                    writer.write(svalue)

            elif ftype is UnicodeType:
                svalue = svalue.encode()
                dump_uvarint(writer, len(svalue))
                writer.write(svalue)

            elif issubclass(ftype, MessageType):
                ffields = field_cache.get(ftype)
                if ffields is None:
                    ffields = ftype.get_fields()
                    field_cache[ftype] = ffields
                dump_uvarint(writer, count_message(svalue, field_cache))
                dump_message(writer, svalue, field_cache)

            else:
                raise TypeError


def count_message(msg: MessageType, field_cache: FieldCache = None) -> int:
    nbytes = 0
    repvalue = [0]

    if field_cache is None:
        field_cache = {}
    fields = field_cache.get(type(msg))
    if fields is None:
        fields = msg.get_fields()
        field_cache[type(msg)] = fields

    for ftag in fields:
        fname, ftype, fdefault = fields[ftag]

        fvalue = getattr(msg, fname, None)
        if fvalue is None:
            continue

        fkey = (ftag << 3) | ftype.WIRE_TYPE

        if fdefault is not FLAG_REPEATED:
            repvalue[0] = fvalue
            fvalue = repvalue

        # length of all the field keys
        nbytes += count_uvarint(fkey) * len(fvalue)

        if ftype is UVarintType:
            for svalue in fvalue:
                nbytes += count_uvarint(svalue)

        elif ftype is SVarintType:
            for svalue in fvalue:
                nbytes += count_uvarint(sint_to_uint(svalue))

        elif ftype is BoolType:
            for svalue in fvalue:
                nbytes += count_uvarint(int(svalue))

        elif isinstance(ftype, EnumType):
            for svalue in fvalue:
                nbytes += count_uvarint(svalue)

        elif ftype is BytesType:
            for svalue in fvalue:
                if isinstance(svalue, list):
                    svalue = _count_bytes_list(svalue)
                else:
                    svalue = len(svalue)
                nbytes += count_uvarint(svalue)
                nbytes += svalue

        elif ftype is UnicodeType:
            for svalue in fvalue:
                svalue = len(svalue.encode())
                nbytes += count_uvarint(svalue)
                nbytes += svalue

        elif issubclass(ftype, MessageType):
            for svalue in fvalue:
                fsize = count_message(svalue, field_cache)
                nbytes += count_uvarint(fsize)
                nbytes += fsize

        else:
            raise TypeError

    return nbytes


def _count_bytes_list(svalue: List[bytes]) -> int:
    res = 0
    for x in svalue:
        res += len(x)
    return res