import asyncio
import struct
from collections.abc import AsyncIterator


async def capture_frames(
    channel: str, quality: str, interval: int
) -> AsyncIterator[bytes]:
    """Capture frames from a Twitch stream using streamlink + ffmpeg.

    Yields JPEG frames as bytes at the specified interval.
    """
    streamlink_cmd = [
        "streamlink",
        "--stdout",
        f"https://twitch.tv/{channel}",
        quality,
    ]

    ffmpeg_cmd = [
        "ffmpeg",
        "-i", "pipe:0",
        "-vf", f"fps=1/{interval}",
        "-f", "image2pipe",
        "-vcodec", "mjpeg",
        "-q:v", "5",
        "pipe:1",
    ]

    streamlink_proc = await asyncio.create_subprocess_exec(
        *streamlink_cmd,
        stdout=asyncio.subprocess.PIPE,
        stderr=asyncio.subprocess.DEVNULL,
    )

    ffmpeg_proc = await asyncio.create_subprocess_exec(
        *ffmpeg_cmd,
        stdin=streamlink_proc.stdout,
        stdout=asyncio.subprocess.PIPE,
        stderr=asyncio.subprocess.DEVNULL,
    )

    # Release streamlink's stdout so ffmpeg owns the pipe
    streamlink_proc.stdout = None

    try:
        buf = b""
        while True:
            chunk = await ffmpeg_proc.stdout.read(65536)
            if not chunk:
                break
            buf += chunk

            # Extract complete JPEG frames (SOI: FF D8, EOI: FF D9)
            while True:
                soi = buf.find(b"\xff\xd8")
                if soi == -1:
                    buf = b""
                    break
                eoi = buf.find(b"\xff\xd9", soi + 2)
                if eoi == -1:
                    # Keep from SOI onward, discard junk before
                    buf = buf[soi:]
                    break
                frame = buf[soi : eoi + 2]
                buf = buf[eoi + 2 :]
                yield frame
    finally:
        for proc in (ffmpeg_proc, streamlink_proc):
            try:
                proc.terminate()
            except ProcessLookupError:
                pass
        await asyncio.gather(
            ffmpeg_proc.wait(), streamlink_proc.wait(), return_exceptions=True
        )