"""`thumbnail_to_jpg`: robustly turn a downloaded thumbnail into a real JPEG poster/og:image.

This replaced yt-dlp's `FFmpegThumbnailsConvertor`, whose `-bsf:v mjpeg2jpeg` path crashed on some
already-JPEG thumbnails (Reddit serves a JPEG under a `.png` name) — and because a postprocessor
error is fatal, it used to fail the WHOLE download. The key regression property here is that a bad
thumbnail returns None (poster falls back to a cut frame) instead of raising.
"""
import shutil
import subprocess
from pathlib import Path

import pytest

from app.downloads import edit

_ffmpeg_missing = shutil.which("ffmpeg") is None
needs_ffmpeg = pytest.mark.skipif(_ffmpeg_missing, reason="ffmpeg not available")


def _is_jpeg(p: Path) -> bool:
    return p.exists() and p.read_bytes()[:3] == b"\xff\xd8\xff"


@needs_ffmpeg
def test_converts_a_png_to_a_real_jpeg(tmp_path):
    src = tmp_path / "thumb.png"
    subprocess.run(
        ["ffmpeg", "-y", "-loglevel", "error", "-f", "lavfi",
         "-i", "color=c=red:s=64x64", "-frames:v", "1", str(src)],
        check=True,
    )
    out = edit.thumbnail_to_jpg(src, tmp_path / "poster.jpg")
    assert out is not None and _is_jpeg(out)


def test_returns_none_for_a_missing_source(tmp_path):
    assert edit.thumbnail_to_jpg(None, tmp_path / "p.jpg") is None
    assert edit.thumbnail_to_jpg(tmp_path / "nope.png", tmp_path / "p.jpg") is None


@needs_ffmpeg
def test_returns_none_on_garbage_input_instead_of_raising(tmp_path):
    # The whole point: a thumbnail ffmpeg can't decode must NOT crash the download.
    bad = tmp_path / "bad.png"
    bad.write_bytes(b"this is definitely not an image")
    assert edit.thumbnail_to_jpg(bad, tmp_path / "p.jpg") is None