import asyncio
from pathlib import Path
import shutil
import subprocess

FFMPEG_BIN = shutil.which("ffmpeg") or "ffmpeg"

async def transcode_to_mobile_mp4(src: Path) -> Path:
    """
    Перекодировать видео в MP4, совместимый с мобильными клиентами Telegram:
    - H.264 (libx264), профиль main
    - pix_fmt yuv420p
    - movflags +faststart
    - AAC 128k
    Возвращает путь к новому файлу (.tg.mp4).
    """
    if not src.exists():
        raise FileNotFoundError(f"Source file not found: {src}")

    dst = src.with_suffix(".tg.mp4")
    cmd = [
        FFMPEG_BIN,
        "-y",
        "-i", str(src),
        "-c:v", "libx264",
        "-preset", "veryfast",
        "-crf", "23",
        "-profile:v", "main",
        "-pix_fmt", "yuv420p",
        "-movflags", "+faststart",
        "-c:a", "aac",
        "-b:a", "128k",
        str(dst),
    ]

    def _run():
        proc = subprocess.run(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        if proc.returncode != 0:
            raise RuntimeError(f"ffmpeg failed: {proc.stderr.decode('utf-8', errors='ignore')}")

    loop = asyncio.get_running_loop()
    await loop.run_in_executor(None, _run)

    if not dst.exists():
        raise RuntimeError("Transcode failed: output file not created")
    return dst