# SPDX-License-Identifier: MIT

from __future__ import annotations

import struct
from typing import IO, TYPE_CHECKING, ClassVar, Generator, Optional, Tuple

from .errors import DiscordException

__all__ = (
    "OggError",
    "OggPage",
    "OggStream",
)


class OggError(DiscordException):
    """An exception that is thrown for Ogg stream parsing errors."""

    pass


# https://tools.ietf.org/html/rfc3533
# https://tools.ietf.org/html/rfc7845


class OggPage:
    _header: ClassVar[struct.Struct] = struct.Struct("<xBQIIIB")
    if TYPE_CHECKING:
        flag: int
        gran_pos: int
        serial: int
        pagenum: int
        crc: int
        segnum: int

    def __init__(self, stream: IO[bytes]) -> None:
        try:
            header = stream.read(struct.calcsize(self._header.format))

            (
                self.flag,
                self.gran_pos,
                self.serial,
                self.pagenum,
                self.crc,
                self.segnum,
            ) = self._header.unpack(header)

            self.segtable: bytes = stream.read(self.segnum)
            bodylen = sum(struct.unpack("B" * self.segnum, self.segtable))
            self.data: bytes = stream.read(bodylen)
        except Exception:
            raise OggError("bad data stream") from None

    def iter_packets(self) -> Generator[Tuple[bytes, bool], None, None]:
        packetlen = offset = 0
        partial = True

        for seg in self.segtable:
            if seg == 255:
                packetlen += 255
                partial = True
            else:
                packetlen += seg
                yield self.data[offset : offset + packetlen], True
                offset += packetlen
                packetlen = 0
                partial = False

        if partial:
            yield self.data[offset:], False


class OggStream:
    def __init__(self, stream: IO[bytes]) -> None:
        self.stream: IO[bytes] = stream

    def _next_page(self) -> Optional[OggPage]:
        head = self.stream.read(4)
        if head == b"OggS":
            return OggPage(self.stream)
        elif not head:
            return None
        else:
            raise OggError("invalid header magic")

    def _iter_pages(self) -> Generator[OggPage, None, None]:
        page = self._next_page()
        while page:
            yield page
            page = self._next_page()

    def iter_packets(self) -> Generator[bytes, None, None]:
        partial = b""
        for page in self._iter_pages():
            for data, complete in page.iter_packets():
                partial += data
                if complete:
                    yield partial
                    partial = b""