"""Whiteboard 的 DAO（文本记事本）。

所有写操作均在该层 commit，service 不直接操作 session。
get_or_create 用于「访问即新建」语义（路由 GET /api/wb/{id} 不存在则建）。
"""

from __future__ import annotations

import logging

from sqlalchemy import func, select
from sqlalchemy.exc import IntegrityError
from sqlalchemy.orm import Session

from ..models.whiteboard import Whiteboard

logger = logging.getLogger("zikai.whiteboard")


class WhiteboardDAO:
    def __init__(self, db: Session) -> None:
        self.db = db

    def create(self, board: Whiteboard) -> Whiteboard:
        self.db.add(board)
        self.db.commit()
        self.db.refresh(board)
        return board

    def get(self, board_id: str) -> Whiteboard | None:
        stmt = select(Whiteboard).where(Whiteboard.board_id == board_id).limit(1)
        return self.db.scalars(stmt).first()

    def get_or_create(self, board_id: str) -> Whiteboard:
        """存在则返回，否则新建空板。利用 unique 约束兜底并发首访。

        仅 IntegrityError（并发下另一事务已插入违反唯一约束）才回滚重读；
        其他异常向上抛，避免掩盖 schema/连接等真实故障。
        """
        board = self.get(board_id)
        if board is not None:
            return board
        board = Whiteboard(board_id=board_id, content="", version=0, edit_count=0)
        try:
            return self.create(board)
        except IntegrityError:
            # 并发下另一事务已插入：回滚后重新读
            self.db.rollback()
            return self.get(board_id)  # type: ignore[return-value]

    def update_content(self, board_id: str, content: str) -> Whiteboard | None:
        """整体替换文本内容，version +1、edit_count +1。"""
        board = self.get(board_id)
        if board is None:
            return None
        board.content = content
        board.version = (board.version or 0) + 1
        board.edit_count = (board.edit_count or 0) + 1
        self.db.commit()
        self.db.refresh(board)
        return board

    def list_all(self, limit: int = 100, offset: int = 0) -> list[Whiteboard]:
        stmt = (
            select(Whiteboard)
            .order_by(Whiteboard.updated_at.desc())
            .limit(limit)
            .offset(offset)
        )
        return list(self.db.scalars(stmt).all())

    def count(self) -> int:
        return self.db.scalar(select(func.count()).select_from(Whiteboard)) or 0

    def delete(self, board_id: str) -> bool:
        board = self.get(board_id)
        if board is None:
            return False
        self.db.delete(board)
        self.db.commit()
        return True