"""服务端托管的预设头像（白名单文件名）。"""

from __future__ import annotations

from pathlib import Path

_PRESETS_DIR = Path(__file__).resolve().parent / "avatar_presets"

# 与仓库内静态文件一致：01.png … 08.png
ALLOWED_PRESET_FILENAMES: frozenset[str] = frozenset(f"{i:02d}.png" for i in range(1, 9))

PRESET_IDS: tuple[str, ...] = tuple(f"{i:02d}" for i in range(1, 9))


def preset_filename_for_id(preset_id: str) -> str | None:
    """preset_id 形如 \"01\"，返回 \"01.png\"；非法则 None。"""
    stripped = preset_id.strip()
    name = f"{stripped}.png"
    if name in ALLOWED_PRESET_FILENAMES:
        return name
    return None


def avatar_url_for_preset_filename(filename: str) -> str:
    return f"/api/auth/avatar-presets/{filename}"


def list_preset_items() -> list[tuple[str, str]]:
    """(preset_id, avatar_url) 列表，供 GET /avatar-presets。"""
    return [
        (pid, avatar_url_for_preset_filename(f"{pid}.png")) for pid in PRESET_IDS
    ]


def preset_file_path(filename: str) -> Path | None:
    if filename not in ALLOWED_PRESET_FILENAMES:
        return None
    path = (_PRESETS_DIR / filename).resolve()
    try:
        path.relative_to(_PRESETS_DIR.resolve())
    except ValueError:
        return None
    return path


def _avatar_upload_stem_allowed(stem: str) -> bool:
    """允许 UUID、数字 ID、含连字符/下划线的安全文件名主干。"""
    if not stem or len(stem) > 128:
        return False
    return all(c.isalnum() or c in "-_" for c in stem)


def safe_avatar_upload_path(filename: str, avatar_dir: Path) -> Path | None:
    """用户上传头像文件名形如 {user_id}.jpg，防路径穿越。"""
    if "/" in filename or "\\" in filename or ".." in filename:
        return None
    if not filename.endswith(".jpg"):
        return None
    stem = filename[:-4]
    if not _avatar_upload_stem_allowed(stem):
        return None
    base = avatar_dir.resolve()
    path = (avatar_dir / filename).resolve()
    try:
        path.relative_to(base)
    except ValueError:
        return None
    return path