"""按服务端会话身份映射文件根，虚拟路径保持不变。"""
import hashlib
from pathlib import Path

import config


def session_root(user_name: str, session_id: str) -> Path:
    # 哈希避免用户名或外部 ID 成为路径片段；不迁移旧共享文件以免猜错归属。
    user_key = hashlib.sha256(user_name.encode()).hexdigest()
    session_key = hashlib.sha256(session_id.encode()).hexdigest()
    root = config.ROOT / "data" / "workspaces" / user_key / session_key
    root.mkdir(parents=True, exist_ok=True)
    return root


def backend_for_runtime(runtime):
    from deepagents.backends import CompositeBackend, FilesystemBackend
    from langgraph.config import get_config
    # 文件工具传 ToolRuntime；模型中间件传不含 config 的 Runtime。
    runtime_config = getattr(runtime, "config", None)
    if runtime_config is None:
        runtime_config = get_config()
    configurable = runtime_config.get("configurable", {})
    user = configurable.get("workspace_user")
    session = configurable.get("workspace_session")
    if not user or not session:
        raise ValueError("文件后端缺少服务端会话身份")
    root = session_root(user, session)
    for directory in ("workspace", "conversation_history"):
        (root / directory).mkdir(exist_ok=True)
    return CompositeBackend(
        default=FilesystemBackend(root_dir=root, virtual_mode=True),
        routes={"/skills/": FilesystemBackend(root_dir=config.ROOT / "skills", virtual_mode=True)},
    )