from __future__ import annotations

from typing import AsyncIterator

from .aes_gcm_siv_stream import MAGIC as _MAGIC, VERSION as _VER, SCHEME_AES_GCM_SIV
from .aes_gcm_siv_stream import decrypt_encf_to_file as _dec_gcmsiv
from .aes_gcm_stream import SCHEME_AES_GCM, decrypt_encf_to_file as _dec_gcm
from .aes_siv_stream import decrypt_encf_to_file as _dec_siv


async def decrypt_encf_auto(byte_iter: AsyncIterator[bytes], key: bytes, out_path: str) -> None:
    """
    Detect scheme by peeking header, then delegate to proper decrypter.
    Re-feeds the peeked bytes back to the chosen decoder.
    """
    buf = bytearray()

    async def _fill(n: int):
        nonlocal buf
        while len(buf) < n:
            try:
                ch = await byte_iter.__anext__()
            except StopAsyncIteration:
                break
            if ch:
                buf.extend(ch)

    await _fill(11)
    if buf[:4] != _MAGIC:
        raise ValueError("bad magic")
    scheme = buf[5]

    async def _prepend_iter():
        nonlocal buf
        if buf:
            yield bytes(buf)
        async for ch in byte_iter:
            yield ch

    if scheme == SCHEME_AES_GCM_SIV:
        await _dec_gcmsiv(_prepend_iter(), key, out_path)
    elif scheme == SCHEME_AES_GCM:
        await _dec_gcm(_prepend_iter(), key, out_path)
    else:
        await _dec_siv(_prepend_iter(), key, out_path)