"""多会话持久化管理模块。

每个会话对应一个独立的 JSON 文件存储在 ./sessions/ 目录下。
"""

import json
import os
import uuid
import tempfile
from datetime import datetime, timezone
from pathlib import Path
from typing import Optional

from dotenv import load_dotenv

from backend.logger import get_logger

load_dotenv()

_session_log = get_logger("session")

SESSIONS_DIR = Path(os.getenv("SESSIONS_DIR", "./sessions"))


def _ensure_dir():
    SESSIONS_DIR.mkdir(parents=True, exist_ok=True)


def _session_path(session_id: str) -> Path:
    return SESSIONS_DIR / f"{session_id}.json"


def generate_session_id() -> str:
    return uuid.uuid4().hex[:12]


def create_session(name: str = "", agent_state: Optional[dict] = None,
                   session_id: Optional[str] = None) -> dict:
    """创建新会话，返回会话元数据。session_id 可选——传入时使用指定 ID。"""
    _ensure_dir()
    sid = session_id or generate_session_id()
    now = _now_iso()
    agent_state = agent_state or {}
    agent_state["session_id"] = sid
    data = {
        "session_id": sid,
        "session_name": name or f"新建报表 {now[:10]}",
        "created_at": now,
        "updated_at": now,
        "agent_state": agent_state,
    }
    with open(_session_path(sid), "w", encoding="utf-8") as f:
        json.dump(data, f, ensure_ascii=False, indent=2)
    _session_log.info("创建会话", extra={"session_id": sid, "session_name": data["session_name"]})
    return data


def load_session(session_id: str) -> Optional[dict]:
    """按 ID 加载会话数据。未找到则返回 None。"""
    _ensure_dir()
    fp = _session_path(session_id)
    if not fp.exists():
        return None
    with open(fp, "r", encoding="utf-8") as f:
        return json.load(f)


def save_session(session_id: str, agent_state: dict, session_name: str = ""):
    """将会话状态原子保存至磁盘（temp file + rename，避免崩溃时截断）。"""
    _ensure_dir()
    fp = _session_path(session_id)
    data = {}
    if fp.exists():
        with open(fp, "r", encoding="utf-8") as f:
            data = json.load(f)

    data["session_id"] = session_id
    if session_name:
        data["session_name"] = session_name
    if not data.get("session_name"):
        data["session_name"] = f"报表 {data.get('created_at', _now_iso())[:10]}"
    data["updated_at"] = _now_iso()
    if not data.get("created_at"):
        data["created_at"] = data["updated_at"]
    data["agent_state"] = agent_state

    # 原子写入：先写临时文件，再 replace，避免崩溃时截断 JSON
    tmp = tempfile.NamedTemporaryFile(
        mode="w", suffix=".json", delete=False,
        dir=SESSIONS_DIR, encoding="utf-8",
    )
    try:
        json.dump(data, tmp, ensure_ascii=False, indent=2)
        tmp.flush()
        os.fsync(tmp.fileno())
        tmp.close()
        os.replace(tmp.name, str(fp))
    except Exception:
        tmp.close()
        Path(tmp.name).unlink(missing_ok=True)
        raise


def get_session_state(session_id: str) -> Optional[dict]:
    """获取会话的完整 agent_state，用于 REST API。

    返回 dict 包含 session_id, session_name, created_at, updated_at, agent_state。
    未找到则返回 None。
    """
    return load_session(session_id)


def list_all_sessions() -> list[dict]:
    """列出所有历史会话（仅摘要，不含完整 agent_state）。"""
    _ensure_dir()
    sessions = []
    for fp in sorted(SESSIONS_DIR.glob("*.json"), key=os.path.getmtime, reverse=True):
        try:
            with open(fp, "r", encoding="utf-8") as f:
                data = json.load(f)
            sessions.append({
                "session_id": data.get("session_id", fp.stem),
                "session_name": data.get("session_name", fp.stem),
                "created_at": data.get("created_at", ""),
                "updated_at": data.get("updated_at", ""),
            })
        except (json.JSONDecodeError, KeyError):
            continue
    return sessions


def delete_session(session_id: str) -> bool:
    """按 ID 删除会话文件。"""
    _ensure_dir()
    fp = _session_path(session_id)
    if fp.exists():
        fp.unlink()
        _session_log.info("删除会话", extra={"session_id": session_id})
        return True
    return False


def _now_iso() -> str:
    return datetime.now(timezone.utc).isoformat()