from contextlib import contextmanager
from core import get_logger, settings, DatabaseException
import pandas as pd
from sqlalchemy import create_engine, text
from sqlalchemy.orm import sessionmaker
from sqlalchemy.exc import SQLAlchemyError

logger = get_logger("database.mysql")


class MySqlDatabaseHelper:
    _instance = None

    def __new__(cls):
        if not cls._instance:
            cls._instance = super(MySqlDatabaseHelper, cls).__new__(cls)
            cls._instance._initialized = False
        return cls._instance

    def __init__(self):
        if self._initialized:
            return
        self._connect_database()
        self._initialized = True

    def _connect_database(self):
        try:
            conn_str = (
                f"mysql+pymysql://{settings.mysql_user}:{settings.mysql_password}"
                f"@{settings.mysql_host}:{settings.mysql_port}/{settings.mysql_db}"
            )
            self.engine = create_engine(
                conn_str,
                pool_size=20,
                max_overflow=30,
                pool_recycle=1800,
                pool_pre_ping=True,
                isolation_level="READ COMMITTED",
            )
            self._DBSession = sessionmaker(bind=self.engine)
            logger.info("MySQL connection pool created", extra={"extra_data": {"host": settings.mysql_host, "db": settings.mysql_db}})
        except Exception as e:
            logger.error("Failed to create MySQL connection", exc_info=True)
            raise DatabaseException(message="数据库连接失败", detail=str(e))

    @contextmanager
    def get_session(self):
        session = self._DBSession()
        try:
            yield session
        except SQLAlchemyError as e:
            session.rollback()
            logger.error("Database operation failed", exc_info=True)
            raise DatabaseException(message="数据库操作失败", detail=str(e))
        finally:
            session.close()

    def load_data_with_page(self, query, params, page_size=100000):
        """分页查询数据"""
        count_query = text(f"SELECT COUNT(*) FROM ({query}) AS _count_subq")
        query += " LIMIT :limit OFFSET :offset"
        query = text(query)

        result = self.fetch_one(count_query, params)
        total_rows = result[0] if result is not None else 0

        if total_rows == 0:
            logger.debug("Query returned 0 rows")
            return pd.DataFrame()

        logger.debug(f"Loading {total_rows} rows with page_size={page_size}")
        data = pd.DataFrame()
        page = 1
        while True:
            offset = (page - 1) * page_size
            page_params = dict(params)
            page_params["limit"] = page_size
            page_params["offset"] = offset

            df = pd.DataFrame(self.fetch_all(query, page_params))
            if df.empty:
                break
            data = pd.concat([data, df], ignore_index=True)
            page += 1

        logger.debug(f"Loaded {len(data)} rows in {page - 1} pages")
        return data

    def fetch_all(self, query, params=None):
        """执行SQL查询并返回所有结果"""
        with self.get_session() as session:
            results = session.execute(query, params or {}).fetchall()
            return results

    def fetch_one(self, query, params=None):
        """执行SQL查询并返回单条结果"""
        with self.get_session() as session:
            result = session.execute(query, params or {}).fetchone()
            return result

    def insert_data(self, table_name, data_dict):
        """插入单条数据到指定表"""
        if not data_dict:
            return 0

        columns = ", ".join(data_dict.keys())
        values = ", ".join([f":{key}" for key in data_dict.keys()])
        query = text(f"INSERT INTO {table_name} ({columns}) VALUES ({values})")

        with self.get_session() as session:
            result = session.execute(query, data_dict)
            session.commit()
            logger.info(f"Inserted 1 row into {table_name}")
            return result.rowcount

    def update_data(self, table_name, update_dict, conditions, condition_params=None):
        """更新表中符合条件的数据"""
        if not update_dict:
            return 0

        set_clause = ", ".join([f"{key} = :{key}" for key in update_dict.keys()])

        if len(conditions) == 1:
            where_clause = f"WHERE {conditions[0]}"
        elif len(conditions) > 1:
            where_clause = f"WHERE {' AND '.join(conditions)}"
        else:
            where_clause = ""

        query = text(f"UPDATE {table_name} SET {set_clause} {where_clause}")

        params = update_dict.copy()
        if condition_params:
            params.update(condition_params)

        with self.get_session() as session:
            result = session.execute(query, params)
            session.commit()
            logger.info(f"Updated {result.rowcount} rows in {table_name}")
            return result.rowcount

    def execute_query(self, query, params=None):
        """执行SQL语句"""
        with self.get_session() as session:
            session.execute(query, params or {})
            session.commit()

    def check_connection(self) -> bool:
        """检查数据库连接是否正常"""
        try:
            self.fetch_one(text("SELECT 1"), {})
            return True
        except Exception:
            return False