using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Text;
using Microsoft.Practices.EnterpriseLibrary.Data;
using System.Globalization;
using System.Data;

namespace DSWeb.Areas.CommMng.DAL
{
    public class PagerHelper
    {
        /// <summary>
        /// 将原始SQL语句修改为分页SQL语句
        /// ※只针对未进行SQL分页的SQL语句使用！
        /// ※原始语句中必须存在ORDER BY 排序！
        /// ※ORDER BY字段不可使用别名
        /// ※只适用于SQL语句中所有关键字为大写的情况下使用！
        /// ※只适用于where条件中不存在子查询的语句,例(WHERE a.id in (SELECT id FROM b))为不可用。
        ///   若必须在where条件中添加子查询，请将子查询的FROM写成小写,例(WHERE a.id in (SELECT id from b))为可用。
        /// </summary>
        /// <param name="OriginalSQLStr">原SQL语句</param>
        /// <param name="start">开始位置</param>
        /// <param name="limit">每页条数</param>
        /// <param name="total">总页数</param>
        /// <returns>新的分页SQL语句</returns>
        public static StringBuilder PageSQL ( string OriginalSQLStr, int start, int limit,out int total) { 
          
            //最后一个orderby语句位置
            CompareInfo Compare = CultureInfo.InvariantCulture.CompareInfo;
            int orderByIndex = Compare.LastIndexOf(OriginalSQLStr, "order by", CompareOptions.IgnoreCase);

            //最后一个orderby语句
            string orderByStatments = "";

            //主查询语句
            string mainSql = OriginalSQLStr;

            if (orderByIndex>0)
            {
                orderByStatments = OriginalSQLStr.Substring(orderByIndex, OriginalSQLStr.Length - orderByIndex);
                //  判断最后一个orderby语句是否在某个子查询里
                //      如果是，则取消新查询语句的orderby拼凑
                //      如果否，则删除原SQL语句中的orderby语句，等待拼凑新orderby语句
                if (orderByStatments.IndexOf(")") > 0)
                {
                    orderByStatments = "";
                }
                else
                {
                    mainSql = OriginalSQLStr.Substring(0, orderByIndex);
                }
            }

            //更改主查询语句的select部分以及orderby语句
            string numColumn = " row_number() over ("+orderByStatments+") as num,";
            mainSql = mainSql.Insert(7,numColumn);
            //创建新SQL主体
            StringBuilder sb = new StringBuilder();
            sb.Append("select * from (");
            sb.Append(mainSql);
            sb.Append(") as t ");
            int endindex = start+limit;
            sb.Append("where t.num>" + start + " and t.num<=" + endindex+" order by t.num");

            //总行数
            total = getTotelForSqlNew(OriginalSQLStr);
            return sb;
        }

        public static int getTotelForSql (string OriginalSQLStr)
        {
            //最后一个orderby语句位置
            CompareInfo Compare = CultureInfo.InvariantCulture.CompareInfo;
            int orderByIndex = Compare.LastIndexOf(OriginalSQLStr, "order by", CompareOptions.IgnoreCase);

            //最后一个orderby语句
            string orderByStatments = "";

            //主查询语句
            string mainSql = OriginalSQLStr;

            if (orderByIndex > 0)
            {
                orderByStatments = OriginalSQLStr.Substring(orderByIndex, OriginalSQLStr.Length - orderByIndex);
                //  判断最后一个orderby语句是否在某个子查询里
                //      如果是，则取消新查询语句的orderby拼凑
                //      如果否，则删除原SQL语句中的orderby语句，等待拼凑新orderby语句
                if (!(orderByStatments.IndexOf(")") > 0))
                {
                    mainSql = OriginalSQLStr.Substring(0, orderByIndex);
                }
            }

            //修改SELECT部分
            //获取最后一个FROM部分
            int fromIndex = Compare.LastIndexOf(mainSql,"FROM",CompareOptions.None);
            string newSql = mainSql.Remove(7, fromIndex - 7);
            newSql = newSql.Insert(7, " count(*) ");

            Database db = DatabaseFactory.CreateDatabase();
            int totel=0;
            using (IDataReader reader = db.ExecuteReader(CommandType.Text, newSql))
            {
                while (reader.Read())
                {
                    totel = Convert.ToInt32(reader[0]);
                }
            }
            return totel;
        }

        public static int getTotelForSqlNew(string OriginalSQLStr)
        {
            //最后一个orderby语句位置
            CompareInfo Compare = CultureInfo.InvariantCulture.CompareInfo;
            int orderByIndex = Compare.LastIndexOf(OriginalSQLStr, "order by", CompareOptions.IgnoreCase);

            //最后一个orderby语句
            string orderByStatments = "";

            //主查询语句
            string mainSql = OriginalSQLStr;

            if (orderByIndex > 0)
            {
                orderByStatments = OriginalSQLStr.Substring(orderByIndex, OriginalSQLStr.Length - orderByIndex);
                //  判断最后一个orderby语句是否在某个子查询里
                //      如果是，则取消新查询语句的orderby拼凑
                //      如果否，则删除原SQL语句中的orderby语句，等待拼凑新orderby语句
                if (!(orderByStatments.IndexOf(")") > 0))
                {
                    mainSql = OriginalSQLStr.Substring(0, orderByIndex);
                }
            }
            string newSql = mainSql.Insert(0, "select COUNT(*) from ( ");
            newSql = newSql + " ) t1 ";
            

            Database db = DatabaseFactory.CreateDatabase();
            int totel = Convert.ToInt32(db.ExecuteScalar(CommandType.Text,newSql));
            
            return totel;
        }
    }
}