package com.dong.java.test;

import java.util.HashMap;
import java.util.Map;

public class CheckSQL {

    private static String[] DBNAMES={""};

    private static String[] keywords={"alter ","create ", "delete ", "do ", "drop ", "handler ", "insert ", "load data infile ", "rename ",
        "replace ", "subquery ", "truncate ", "update "};
    
    /**
     * 检查输入的sql
     * @param sql
     * @return
     */
    public boolean checkSql(String sql) {
        sql=sql.toLowerCase();
        if(!sql.startsWith("select")) { // sql不是以select开头
            return false;
        }
        for(String keyword: keywords) {
            if(sql.indexOf(keyword) >= 0) { // sql中包含不支持的关键字
                return false;
            }
        }

        String[] dbs=DBNAMES;
        String[] sqlsFrom=sql.split(" from ");
        String[] sqlsJoin=sql.split(" join ");
        Map<String, String> fromMap=dbname(sqlsFrom);
        Map<String, String> joinMap=dbname(sqlsJoin);
        
        fromMap.putAll(joinMap);
        for(String s: fromMap.keySet()) { // 配对sql中的数据库名和允许的数据库
            boolean flag=false;
            for(String db: dbs) {
                if(db.equals(s)) {
                    flag=true;
                }
            }
            if(flag == false) { // 如果有一个不匹配，为false
                return false;
            }
        }
        return true;
    }

    public Map<String, String> dbname(String[] sql) {
        Map<String, String> names=new HashMap<String, String>();

        if(sql.length > 1) {
            for(int i=0; i < sql.length; i++) {
                if(i == 0) {
                    continue;
                }
                String s=sql[i].split("\\.")[0];
                if(s.charAt(0) >= 'a' && s.charAt(0) <= 'z') {
                    names.put(s.trim(), s.trim());
                }
            }
        }
        return names;
    }
}