"""对象存储 key 生成。

布局：users/{user_id}/kbs/{kb_id}/original/{rand8}_{safe_filename}
      users/{user_id}/kbs/{kb_id}/markdown/{rand8}.md

规则（需求 §27 / §23）：
- 不信任用户文件名：取 basename，剔除路径穿越与控制字符，截断长度。
- 主体是内部 UUID，公共 URL 使用 token，绝不回显此 key。
"""

import re
import secrets
import uuid

_SAFE_NAME_RE = re.compile(r"[^A-Za-z0-9._\-]+")
_MAX_FILENAME_LEN = 120


def sanitize_filename(original: str) -> str:
    name = original.replace("\\", "/").split("/")[-1]
    name = _SAFE_NAME_RE.sub("_", name).strip("._")
    if not name:
        name = "file"
    return name[:_MAX_FILENAME_LEN]


def original_object_key(
    *,
    user_id: str,
    knowledge_base_id: str,
    document_id: str,
    original_filename: str,
) -> str:
    rand = secrets.token_urlsafe(6)  # ~8 字符
    safe = sanitize_filename(original_filename)
    return (
        f"users/{user_id}/kbs/{knowledge_base_id}/docs/{document_id}/original/{rand}_{safe}"
    )


def markdown_object_key(
    *,
    user_id: str,
    knowledge_base_id: str,
    document_id: str,
) -> str:
    rand = secrets.token_urlsafe(6)
    return (
        f"users/{user_id}/kbs/{knowledge_base_id}/docs/{document_id}/markdown/{rand}.md"
    )