import DBService from '../db/DBService'
import logger from '../logger/Logger'
import BaseProvider from '../core/BaseProvider'

const ROW_LIMIT = 2000

export default class MysqlProvider extends BaseProvider {

    async connectDataSource() {
        let dbService = new DBService()
        let inputs = this.params.inputs

        for (let i = 0; i < inputs.length; i++) {
            const input = inputs[i];
            let { topic, table, conditions, fields } = input

            // 首先查询该条件下的数据量大小
            let countSql = `SELECT COUNT(*) as num FROM ${table} WHERE ${conditions}`
            logger.info(countSql)

            let { rows, err } = await dbService.query(countSql, [])

            if (!err) {
                let num = rows[0]["num"]
                // 每次查询200条数据,需要查询的次数
                let queryCount = (num % ROW_LIMIT) > 0 ? Math.floor(num / ROW_LIMIT) + 1 : (Math.floor(num / ROW_LIMIT))
                logger.info(`总共有${num}条数据, 需要查询${queryCount}次`)
                let offset = 0

                for (let i = 0; i < queryCount; i++) {
                    let sql = `SELECT ${fields} FROM ${table} WHERE ${conditions} ORDER BY createTimeStamp LIMIT ${ROW_LIMIT} OFFSET ${offset}`
                    logger.info(sql)
                    let { rows, err } = await dbService.query(sql, [])
                    
                    if (err) {
                        logger.info(err)
                        break
                    }
                    
                    for (let i = 0; i < rows.length; i++) {
                        const row = rows[i];
                        this.onMessage(topic, row)
                    }

                    offset += ROW_LIMIT
                }
            } else {
                logger.info(err)
            }
        }
        
        console.log("输入结束")
        this.core.endInput()
    }
}