"""服务端 Session 管理（MVP: 内存 dict + TTL）。

- Session token: secrets.token_urlsafe(32)
- Cookie: HttpOnly, SameSite=Lax, 生产环境 Secure
- 默认过期: 7 天

未来切换 Redis: 改 _store 为 Redis 客户端，接口不变。
"""

import secrets
import time
from dataclasses import dataclass

from app.core.config import get_settings

# 内存存储：{token: SessionEntry}
_store: dict[str, "SessionEntry"] = {}

SESSION_COOKIE_NAME = "session_id"
SESSION_TTL_SECONDS = 7 * 24 * 3600  # 7 天


@dataclass
class SessionEntry:
    user_id: str
    created_at: float
    last_accessed: float


def create_session(user_id: str) -> str:
    """创建 session，返回 token（写入 Cookie）。"""
    _cleanup_expired()
    token = secrets.token_urlsafe(32)
    now = time.time()
    _store[token] = SessionEntry(user_id=user_id, created_at=now, last_accessed=now)
    return token


def get_session_user(token: str) -> str | None:
    """根据 token 获取 user_id；不存在或过期返回 None。"""
    entry = _store.get(token)
    if entry is None:
        return None
    now = time.time()
    if now - entry.last_accessed > SESSION_TTL_SECONDS:
        _store.pop(token, None)
        return None
    entry.last_accessed = now
    return entry.user_id


def delete_session(token: str) -> None:
    _store.pop(token, None)


def _cleanup_expired() -> None:
    """惰性清理过期 session。"""
    now = time.time()
    expired = [t for t, e in _store.items() if now - e.last_accessed > SESSION_TTL_SECONDS]
    for t in expired:
        _store.pop(t, None)


def get_cookie_params() -> dict:
    """构建 Set-Cookie 参数。"""
    settings = get_settings()
    return {
        "key": SESSION_COOKIE_NAME,
        "httponly": True,
        "samesite": "lax",
        "secure": settings.is_production,
        "max_age": SESSION_TTL_SECONDS,
        "path": "/",
    }