"""用 ffmpeg 在每条 events 记录的 start_offset_sec 处抽一帧，生成缩略图。

供网页事件列表展示预览图，点击缩略图再跳转播放对应视频的完整时间点。

失败重试上限：单个事件连续失败超过 MAX_ATTEMPTS 次后，在 extra_json 里标记
thumbnail_failed，后续运行直接跳过，避免对损坏文件无限重试。
"""
import json
import subprocess

from analysis.config import PROJECT_ROOT, THUMBNAILS_DIR
from analysis.db import get_events, get_video_by_id, update_event_thumbnail, update_event_extra

MAX_ATTEMPTS = 3


def _extract_frame(video_path, offset_sec, output_path):
    # -ss 放在 -i 之后用精确seek：放在 -i 之前的快速seek在临近视频结尾处
    # 会因缺少解码所需的参考帧而失败（HEVC "Could not find ref with POC"）。
    # 录像多为几秒到几十秒的短片，精确seek的性能代价可忽略。
    result = subprocess.run(
        [
            "ffmpeg", "-i", str(video_path), "-ss", str(offset_sec),
            "-frames:v", "1", "-q:v", "3", "-y", str(output_path),
        ],
        capture_output=True, timeout=30,
    )
    return result.returncode == 0 and output_path.exists()


def _get_attempts(event):
    try:
        extra = json.loads(event["extra_json"] or "{}")
        return extra.get("thumbnail_attempts", 0)
    except (json.JSONDecodeError, TypeError):
        return 0


def _increment_attempts(event):
    try:
        extra = json.loads(event["extra_json"] or "{}")
    except (json.JSONDecodeError, TypeError):
        extra = {}
    extra["thumbnail_attempts"] = extra.get("thumbnail_attempts", 0) + 1
    if extra["thumbnail_attempts"] >= MAX_ATTEMPTS:
        extra["thumbnail_failed"] = True
    update_event_extra(event["id"], json.dumps(extra, ensure_ascii=False))


def process_all(limit=None):
    THUMBNAILS_DIR.mkdir(exist_ok=True)
    events = []
    for e in get_events():
        if e["thumbnail_path"]:
            continue
        try:
            extra = json.loads(e["extra_json"] or "{}")
            if extra.get("thumbnail_failed"):
                continue
        except (json.JSONDecodeError, TypeError):
            pass
        events.append(e)

    if limit:
        events = events[:limit]

    video_cache = {}
    processed = 0
    failed = 0
    for event in events:
        video_id = event["video_id"]
        if video_id not in video_cache:
            video_cache[video_id] = get_video_by_id(video_id)
        video = video_cache[video_id]
        if video is None:
            _increment_attempts(event)
            failed += 1
            continue

        video_path = PROJECT_ROOT / video["file_path"]
        if not video_path.exists():
            _increment_attempts(event)
            failed += 1
            continue

        output_path = THUMBNAILS_DIR / f"{event['id']}.jpg"
        offset_sec = event["start_offset_sec"] or 0.0

        if _extract_frame(video_path, offset_sec, output_path):
            update_event_thumbnail(event["id"], str(output_path.relative_to(PROJECT_ROOT)))
            processed += 1
        else:
            _increment_attempts(event)
            failed += 1

    return {"processed": processed, "failed": failed}


if __name__ == "__main__":
    print("===== 开始生成缩略图 =====")
    result = process_all()
    print(f"→ 生成 {result['processed']} 张缩略图，失败 {result['failed']} 条")
    print("===== 生成完成 =====")