"""Size and a still frame of a clip, read straight from Zipline with ffprobe/ffmpeg, for Discord's link preview."""
import json
import subprocess
import threading
from functools import lru_cache

# /v/ and /_site/thumb need no login: cap how many ffmpeg/ffprobe processes they can start at once
SLOTS = threading.BoundedSemaphore(2)


@lru_cache(maxsize=256)
def video_size(url: str, length: str) -> tuple[int, int] | None:
    """(width, height) of the first video stream; `length` is only part of the cache key (a reused name)."""
    cmd = ["ffprobe", "-v", "error", "-select_streams", "v:0",
           "-show_entries", "stream=width,height", "-of", "json", url]
    try:
        with SLOTS:
            result = subprocess.run(cmd, capture_output=True, timeout=10)
        stream = json.loads(result.stdout)["streams"][0]
        return int(stream["width"]), int(stream["height"])
    except (OSError, subprocess.TimeoutExpired, ValueError, KeyError, IndexError):
        return None


@lru_cache(maxsize=64)
def still_jpeg(url: str, length: str) -> bytes | None:
    """One frame (1 s in, or the first one for very short clips) as a JPEG at most 720 px tall."""
    for seek in ("1", "0"):
        cmd = ["ffmpeg", "-v", "error", "-ss", seek, "-i", url, "-frames:v", "1",
               "-vf", "scale=-2:'min(720,ih)'", "-f", "image2", "-c:v", "mjpeg", "pipe:1"]
        try:
            with SLOTS:
                result = subprocess.run(cmd, capture_output=True, timeout=30)
        except (OSError, subprocess.TimeoutExpired):
            return None
        if result.returncode == 0 and result.stdout:
            return result.stdout
    return None