using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.EntityFrameworkCore;

namespace Common.Helper.Page
{
    /// <summary>
    /// 分页帮助类
    /// </summary>
    public class PageHelper
    {
      /*
      *  1.分页 list.Skip(x).Take(y);
      *  2.(x,y)超过(0,list.Count)范围时list为空[],在范围内(或单边超过范围)时显示范围内数据
      */
        /// <summary>
        /// 分页
        /// </summary>
        /// <typeparam name="T">数据类型</typeparam>
        /// <param name="list">数据</param>
        /// <param name="page">页码</param>
        /// <param name="size">数据量/页</param>
        /// <returns></returns>
        public static Data Pagination<T>(List<T> list, int page, int size)
        {
            if (list == null)
                return new Data(0, page, null);
            if (list.Count != 0 && list.Count >= size)
                return new Data(list.Count, page <= 0 ? 0 : page,
                    list.Skip(Convert.ToInt32((page <= 0 ? 0 : page - 1) * size)).Take(size).ToList());
            return new Data(list.Count, page, list);
        }

        /// <summary>
        /// 该分页方法适用于sql server 2008 .net core 3.1不支持2008数据库
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="db"></param>
        /// <param name="dbTable"></param>
        /// <param name="page"></param>
        /// <param name="size"></param>
        /// <returns></returns>
        public static Data Pagination<T>(DbContext db, DbSet<T> dbTable, int page, int size) where T : class
        {
            var entityType = db.Model.FindEntityType(typeof(T));
            var tableName = entityType.GetTableName();
            var primaryKeyName = entityType.FindPrimaryKey().Properties.First().Name;
            return new Data(dbTable.Count(), page, dbTable.FromSqlRaw($"select * from (select ROW_NUMBER() OVER(ORDER BY {primaryKeyName}) RowSerialNumber ,* from {tableName}) s where RowSerialNumber BETWEEN {(page - 1) * size + 1} and {page * size}").ToList());
        }
        /// <summary>
        /// 该方法适用于sql server 2008以上的数据库 sql server 2008会报错
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="list"></param>
        /// <param name="page"></param>
        /// <param name="size"></param>
        /// <returns></returns>
        public static Data Pagination<T>(IEnumerable<T> list, int page, int size)
        {
            return list == null ? new Data(0, page, null) : new Data(list.Count(), page, list.Skip(Convert.ToInt32((page <= 0 ? 0 : page - 1) * size)).Take(size).ToList());
        }
    }

    /// <summary>
    /// 数据页数
    /// </summary>
    public class Data
    {
        /// <summary>
        /// 总数
        /// </summary>
        public int? Total { get; set; }
        /// <summary>
        /// 当前页码
        /// </summary>
        public int? Current { get; set; }
        /// <summary>
        /// 数据
        /// </summary>
        public object List { get; set; }

        /// <summary>
        /// 入参
        /// </summary>
        /// <param name="total"></param>
        /// <param name="current"></param>
        /// <param name="list"></param>
        public Data(int? total, int? current, object list)
        {
            Total = total ?? 0;
            Current = current;
            List = list;
        }
    }
}