from config import load_config
import pandas as pd
from sqlalchemy import create_engine, text
from sqlalchemy.orm import sessionmaker
from sqlalchemy.exc import SQLAlchemyError

cfgs = load_config()


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._host = cfgs['mysql']['host']
        self._port = cfgs['mysql']['port']
        self._user = cfgs['mysql']['user']
        self._passwd = cfgs['mysql']['passwd']
        self._dbname = cfgs['mysql']['db']
        
        self.connect_database()
        self._initialized = True
        
    def connect_database(self):
        # 创建数据库连接
        try:
            conn = "mysql+pymysql://" + self._user + ":" + self._passwd + "@" + self._host + ":" + str(self._port) + "/" + self._dbname
        except Exception as e:
            raise ConnectionAbortedError(f"failed to create connection string: {e}")
        
        # 通过连接池创建engine
        self.engine = create_engine(
            conn,
            pool_size=10, # 设置连接池大小
            max_overflow=20, # 超过连接池大小时的额外连接数
            pool_recycle=3600 # 回收连接时间
        )
        
        self._DBSession = sessionmaker(bind=self.engine)
        
    def load_data_with_page(self, query, params, page_size=1000):
        """分页查询数据"""
        data = pd.DataFrame()
        query += " LIMIT :limit OFFSET :offset"
        query = text(query)
        
        page = 1
        while True:
            offset = (page - 1) * page_size # 计算偏移量
            params["limit"] = page_size
            params["offset"] = offset

            df = pd.DataFrame(self.fetch_all(query, params))
            if df.empty:
                break
            data = pd.concat([data, df], ignore_index=True)
            print(f"Page {page}: Retrieved {len(df)} rows, Total rows so far: {len(data)}")
            
            page += 1
        return data
        
        
    def fetch_all(self, query, params=None):
        """执行SQL查询并返回所有结果"""
        session = self._DBSession()
        try:
            results = session.execute(query, params or {}).fetchall()
            return results
        except SQLAlchemyError as e:
            session.rollback()
            print(f"error: {e}")
        finally:
            session.close()
            
    def fetch_one(self, query, params=None):
        """执行SQL查询并返回单条结果"""
        session = self._DBSession()
        try:
            result = session.execute(query, params or {}).fetchone()
            return result
        except SQLAlchemyError as e:
            session.rollback()
            print(f"error: {e}")
        finally:
            session.close()
            
    def execute_query(self, query, params=None):
        """执行SQL语句 (无返回值, 如INSERT, UPDATE, DELETE)"""
        session = self._DBSession()
        try:
            session.execute(query, params or {})
            session.commit()
        except SQLAlchemyError as e:
            session.rollback()
            print(f"Error: {e}")
        finally:
            session.close()