"""
Generate and cache low-bitrate preview proxies for browser playback.

Goal:
- Improve Remotion Player preview smoothness by serving smaller/faster-to-decode videos.
- Keep original `source_path` for accurate export; only swap `source_url` for preview.

Design:
- Deterministic cache key based on (path, mtime, size).
- Proxy lives under config.TEMP_DIR / "proxy".
- Generated with ffmpeg: scale/pad + fps downsample + faststart + no audio.
"""

from __future__ import annotations

import hashlib
import os
from pathlib import Path
from typing import Optional, Tuple

import config
from modules import ffmpeg_utils


def _key_for_file(path: str) -> str:
    st = os.stat(path)
    raw = f"{path}|{st.st_mtime_ns}|{st.st_size}".encode("utf-8")
    return hashlib.sha1(raw).hexdigest()  # short, deterministic


def ensure_video_proxy(
    source_path: str,
    *,
    target_w: int = 540,
    target_h: int = 960,
    target_fps: int = 24,
    crf: int = 28,
    preset: str = "veryfast",
) -> Tuple[Optional[str], Optional[str]]:
    """
    Ensure a preview proxy exists for source_path.

    Returns: (proxy_path, proxy_url) or (None, None) if source_path invalid.
    """
    if not source_path or not os.path.exists(source_path):
        return None, None

    proxy_dir = Path(config.TEMP_DIR) / "proxy"
    proxy_dir.mkdir(parents=True, exist_ok=True)

    key = _key_for_file(source_path)
    out_name = f"proxy_{key}.mp4"
    out_path = proxy_dir / out_name

    if out_path.exists() and out_path.stat().st_size > 1024:
        return str(out_path), f"/static/temp/proxy/{out_name}"

    vf = (
        f"scale={target_w}:{target_h}:force_original_aspect_ratio=decrease,"
        f"pad={target_w}:{target_h}:(ow-iw)/2:(oh-ih)/2:black,"
        f"fps={target_fps}"
    )

    cmd = [
        ffmpeg_utils.FFMPEG_PATH,
        "-y",
        "-i",
        source_path,
        "-an",  # preview 不要音轨，减少解码负担（旁白/BGM 走单独轨道）
        "-vf",
        vf,
        "-c:v",
        "libx264",
        "-preset",
        preset,
        "-crf",
        str(crf),
        "-tune",
        "fastdecode",
        "-pix_fmt",
        "yuv420p",
        "-movflags",
        "+faststart",
        str(out_path),
    ]

    ffmpeg_utils._run_ffmpeg(cmd)
    if out_path.exists() and out_path.stat().st_size > 1024:
        return str(out_path), f"/static/temp/proxy/{out_name}"
    return None, None