package com.ediagnosis.cdr.dao.sqlutil;


import net.sf.jsqlparser.JSQLParserException;
import net.sf.jsqlparser.expression.Function;
import net.sf.jsqlparser.expression.LongValue;
import net.sf.jsqlparser.parser.CCJSqlParserUtil;
import net.sf.jsqlparser.statement.Statement;
import net.sf.jsqlparser.statement.select.*;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.List;
import java.util.Optional;


public class SqlParser {


    private static final Logger log = LoggerFactory.getLogger(SqlParser.class);

    public static Optional<String> getCountSql(String sql) {
        Optional<PlainSelect> plainSelectOptional = detectSelectSql(sql);
        if (plainSelectOptional.isEmpty()) {
            return Optional.empty();
        }
        PlainSelect plainSelect = plainSelectOptional.get();
        List<SelectItem<?>> selectItems = plainSelect.getSelectItems();
        selectItems.clear();
        selectItems.add(new SelectItem<>(
                        new Function("count", new AllColumns())
                )
        );
        String newSql = plainSelect.toString();
        log.info("change to count sql: {}", newSql);
        return Optional.of(newSql);
    }


    public static String addLimitClause(String sql) {
        String newSql = sql;
        Optional<PlainSelect> plainSelectOptional = detectSelectSql(sql);

        if (plainSelectOptional.isEmpty()) {
            return newSql;
        }
        PlainSelect plainSelect = plainSelectOptional.get();
        Limit limit = plainSelect.getLimit();
        if (limit == null) {
            Select select = plainSelect.withLimit(
                    new Limit()
                            .withRowCount(new LongValue(10))
                            .withOffset(new LongValue(0))
            );
             newSql = select.toString();
            log.info("原始sql没有limit从句,添加limit从句,新sql语句:{}", newSql);
        } else {
            log.info("原始sql存在limit从句，不做处理");
        }
        return newSql;
    }

    private static Optional<PlainSelect> detectSelectSql(String sql) {
        Statement statement = null;
        try {
            statement = CCJSqlParserUtil.parse(sql);
            log.debug("sql语句语法正确");
        } catch (JSQLParserException e) {
            log.error("解析sql失败", e);
            return Optional.empty();
        }
        if ((statement instanceof PlainSelect plainSelect)) {
            log.debug("原始sql是select语句");
            return Optional.of(plainSelect);
        } else {
            log.warn("原始sql不是select语句");
            return Optional.empty();
        }
    }

}