import os
import time
import json
import logging
from pathlib import Path
from typing import Any, Dict, List, Set

from PIL import Image

from . import db

logger = logging.getLogger(__name__)

IMAGE_EXT = {".jpg", ".jpeg", ".png", ".webp"}
THUMB_SIZE = (480, 480)


def _scan_folder(folder: Path) -> List[Dict[str, Any]]:
    """폴더 내 이미지 파일 목록 수집 (os.scandir)."""
    if not folder.exists():
        return []
    items = []
    with os.scandir(folder) as entries:
        for entry in entries:
            if entry.is_file() and Path(entry.name).suffix.lower() in IMAGE_EXT:
                try:
                    mtime = entry.stat().st_mtime
                except OSError as e:
                    logger.warning("Cannot stat %s: %s", entry.path, e)
                    continue
                items.append({
                    "filename": entry.name,
                    "mtime": mtime,
                })
    return items


def _generate_thumb(src: Path, dest: Path) -> bool:
    """원본에서 480x480 썸네일 생성. 성공 시 True."""
    dest.parent.mkdir(parents=True, exist_ok=True)
    tmp = dest.with_name(dest.stem + ".tmp" + dest.suffix)
    try:
        with Image.open(src) as im:
            im.thumbnail(THUMB_SIZE)
            ext = dest.suffix.lower()
            if ext in (".jpg", ".jpeg"):
                fmt = "JPEG"
            elif ext == ".png":
                fmt = "PNG"
            elif ext == ".webp":
                fmt = "WEBP"
            else:
                fmt = (im.format or "").upper() or "JPEG"
            im.save(tmp, format=fmt, quality=85, optimize=True)
        tmp.replace(dest)
        return True
    except Exception as e:
        logger.warning("Thumb generation failed: %s → %s", src, e)
        try:
            if tmp.exists():
                tmp.unlink()
        except Exception:
            pass
        return False


def _load_region_map_merged(region_map_path: Path, thumb_root: Path) -> dict:
    """
    원본 region_map.json + RW 오버라이드 파일 병합.
    원본은 RO 마운트이므로 신규 폴더는 thumb_root/region_map_extra.json에 저장.
    """
    try:
        with open(region_map_path, "r", encoding="utf-8") as f:
            region_map = json.load(f)
    except (FileNotFoundError, json.JSONDecodeError) as e:
        logger.error("Failed to load region_map: %s", e)
        raise

    # 오버라이드 파일 병합
    extra_path = thumb_root / "region_map_extra.json"
    if extra_path.exists():
        try:
            with open(extra_path, "r", encoding="utf-8") as f:
                extra = json.load(f)
            for k, v in extra.items():
                if k in region_map:
                    # 기존 지역에 앨범 추가 (중복 방지)
                    existing = region_map[k]
                    if isinstance(existing, list) and isinstance(v, list):
                        merged = list(dict.fromkeys(existing + v))
                        region_map[k] = merged
                else:
                    region_map[k] = v
        except (json.JSONDecodeError, OSError) as e:
            logger.warning("Failed to load region_map_extra: %s", e)

    return region_map


def _save_extra_albums(thumb_root: Path, new_folders: List[str]) -> None:
    """신규 발견 폴더를 RW 영역의 오버라이드 파일에 저장."""
    extra_path = thumb_root / "region_map_extra.json"
    extra = {}
    if extra_path.exists():
        try:
            with open(extra_path, "r", encoding="utf-8") as f:
                extra = json.load(f)
        except (json.JSONDecodeError, OSError):
            extra = {}

    uncategorized = extra.get("미분류", [])
    existing = set(uncategorized)
    added = [f for f in new_folders if f not in existing]
    if added:
        uncategorized.extend(added)
        extra["미분류"] = uncategorized
        try:
            with open(extra_path, "w", encoding="utf-8") as f:
                json.dump(extra, f, ensure_ascii=False, indent=2)
            logger.info("Saved %d new folders to region_map_extra.json → 미분류", len(added))
        except OSError as e:
            logger.warning("Cannot write region_map_extra: %s", e)


def sync(
    travel_root: Path,
    thumb_root: Path,
    region_map_path: Path,
) -> Dict[str, Any]:
    """
    폴더 스캔 → DB 동기화 + 썸네일 일괄 생성.

    Returns:
        {"added": int, "removed": int, "thumbs_generated": int,
         "discovered": int, "duration_sec": float}
    """
    start = time.time()

    # 1. region_map.json + 오버라이드 병합
    region_map = _load_region_map_merged(region_map_path, thumb_root)

    all_albums: Set[str] = set()
    for v in region_map.values():
        if isinstance(v, list):
            all_albums.update(v)
        elif isinstance(v, dict) and isinstance(v.get("albums"), list):
            all_albums.update(v["albums"])

    # 1-b. 파일시스템에서 신규 폴더 자동 탐색
    discovered = 0
    new_folders = []
    try:
        with os.scandir(travel_root) as entries:
            for entry in entries:
                if not entry.is_dir() or entry.name.startswith("_"):
                    continue
                if entry.name in all_albums:
                    continue
                # 이미지가 하나라도 있는 폴더만 추가
                folder = travel_root / entry.name
                has_images = any(
                    Path(f.name).suffix.lower() in IMAGE_EXT
                    for f in os.scandir(folder)
                    if f.is_file()
                )
                if has_images:
                    all_albums.add(entry.name)
                    new_folders.append(entry.name)
                    discovered += 1
                    logger.info("Discovered new album folder: %s", entry.name)
    except OSError as e:
        logger.warning("Failed to scan travel_root for new folders: %s", e)

    # 신규 폴더를 RW 오버라이드 파일에 영구 저장
    if new_folders:
        _save_extra_albums(thumb_root, new_folders)

    # 2. 각 앨범 폴더 스캔 → DB 배치 동기화
    added = 0
    updated = 0
    removed = 0

    for album in sorted(all_albums):
        folder = travel_root / album
        items = _scan_folder(folder)
        existing_filenames = {item["filename"] for item in items}

        result = db.batch_sync_album(album, items, existing_filenames)
        added += result["added"]
        updated += result["updated"]
        removed += result["removed"]

    # 3. 썸네일 미생성 분 일괄 생성
    no_thumb = db.get_photos_without_thumb()
    thumbs_generated = 0
    thumb_done_batch = []

    for photo in no_thumb:
        src = travel_root / photo["album"] / photo["filename"]
        dest = thumb_root / photo["album"] / photo["filename"]
        if _generate_thumb(src, dest):
            thumb_done_batch.append(photo)
            thumbs_generated += 1

    db.batch_mark_thumbs_done(thumb_done_batch)

    duration = round(time.time() - start, 2)
    logger.info(
        "Sync complete: added=%d updated=%d removed=%d thumbs=%d discovered=%d duration=%.2fs",
        added, updated, removed, thumbs_generated, discovered, duration,
    )

    return {
        "added": added,
        "updated": updated,
        "removed": removed,
        "thumbs_generated": thumbs_generated,
        "discovered": discovered,
        "duration_sec": duration,
    }