"""FFmpeg encoding; this module also works outside Unreal."""
from pathlib import Path
import subprocess

from .paths import executable


def encode(frames, fps, output=None, ffmpeg=None, expected_frames=None):
    frames = Path(frames).resolve()
    if fps <= 0:
        raise ValueError("FPS musi byc dodatni.")
    images = sorted(frames.glob("frame_*.png"))
    count = len(images)
    if not count or any(p.name != f"frame_{i:04d}.png" for i, p in enumerate(images)):
        raise RuntimeError(f"Brak kompletnej numeracji frame_0000.png, frame_0001.png... w {frames}")
    if expected_frames is not None and count != expected_frames:
        raise RuntimeError(f"Render zapisal {count} klatek zamiast {expected_frames}.")
    output = Path(output) if output else frames.parent / "film.mp4"
    output.parent.mkdir(parents=True, exist_ok=True)
    command = [executable("ffmpeg", ffmpeg), "-hide_banner", "-loglevel", "error", "-y",
               "-framerate", str(fps), "-start_number", "0", "-i", str(frames / "frame_%04d.png"),
               "-frames:v", str(count), "-c:v", "libx264", "-crf", "20", "-pix_fmt", "yuv420p",
               "-vf", "pad=ceil(iw/2)*2:ceil(ih/2)*2", "-movflags", "+faststart", str(output)]
    result = subprocess.run(command, capture_output=True, text=True)
    if result.returncode:
        raise RuntimeError("FFmpeg: " + result.stderr[-4000:])
    return output.resolve()