using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Reflection;
using System.Text;

namespace CodeGenerator.Common
{
    /// <summary>
    /// 数据源转换
    /// </summary>
    public static class DataHelper
    {
        #region List转换DataTable
        /// <summary>
        /// 将泛类型集合List类转换成DataTable
        /// </summary>
        /// <param name="list">泛类型集合</param>
        /// <returns></returns>
        public static DataTable ListToDataTable<T>(List<T> entitys)
        {
            //检查实体集合不能为空
            if (entitys == null || entitys.Count < 1)
            {
                throw new Exception("需转换的集合为空");
            }
            //取出第一个实体的所有Propertie
            Type entityType = entitys[0].GetType();
            PropertyInfo[] entityProperties = entityType.GetProperties();

            //生成DataTable的structure
            //生产代码中，应将生成的DataTable结构Cache起来，此处略
            DataTable dt = new DataTable();
            for (int i = 0; i < entityProperties.Length; i++)
            {
                //dt.Columns.Add(entityProperties[i].Name, entityProperties[i].PropertyType);
                dt.Columns.Add(entityProperties[i].Name);
            }
            //将所有entity添加到DataTable中
            foreach (object entity in entitys)
            {
                //检查所有的的实体都为同一类型
                if (entity.GetType() != entityType)
                {
                    throw new Exception("要转换的集合元素类型不一致");
                }
                object[] entityValues = new object[entityProperties.Length];
                for (int i = 0; i < entityProperties.Length; i++)
                {
                    entityValues[i] = entityProperties[i].GetValue(entity, null);
                }
                dt.Rows.Add(entityValues);
            }
            return dt;
        }
        #endregion

        #region DataTable/DataSet 转 XML
        /// <summary>
        /// DataTable 转 XML
        /// </summary>
        /// <param name="dt"></param>
        /// <returns></returns>
        public static string DataTableToXML(DataTable dt)
        {
            if (dt != null)
            {
                if (dt.Rows.Count > 0)
                {
                    System.IO.StringWriter writer = new System.IO.StringWriter();
                    dt.WriteXml(writer);
                    return writer.ToString();
                }
            }
            return String.Empty;
        }
        /// <summary>
        /// DataSet 转 XML
        /// </summary>
        /// <param name="ds"></param>
        /// <returns></returns>
        public static string DataSetToXML(DataSet ds)
        {
            if (ds != null)
            {
                System.IO.StringWriter writer = new System.IO.StringWriter();
                ds.WriteXml(writer);
                return writer.ToString();
            }
            return String.Empty;
        }
        #endregion

        #region DataTable转成List<T>
        /// <summary>
        /// DataTable 转换为List 集合
        /// </summary>
        /// <typeparam name="TResult">类型</typeparam>
        /// <param name="dt">DataTable</param>
        /// <returns></returns>
        public static List<TResult> ToList<TResult>(this DataTable dt) where TResult : class,new()  
        {
            //创建一个属性的列表
            List<PropertyInfo> prlist = new List<PropertyInfo>();
            //获取TResult的类型实例  反射的入口
            Type t = typeof(TResult);
            //获得TResult 的所有的Public 属性 并找出TResult属性和DataTable的列名称相同的属性(PropertyInfo) 并加入到属性列表 
            Array.ForEach<PropertyInfo>(t.GetProperties(), p => { if (dt.Columns.IndexOf(p.Name) != -1) prlist.Add(p); });
            //创建返回的集合
            List<TResult> oblist = new List<TResult>();
            
            foreach (DataRow row in dt.Rows)
            {
                //创建TResult的实例
                TResult ob = new TResult();
                //找到对应的数据  并赋值
                prlist.ForEach(p => { if (row[p.Name] != DBNull.Value) p.SetValue(ob, row[p.Name], null); });
                //放入到返回的集合中.
                oblist.Add(ob);
            }
            return oblist;
        }
        #endregion
    }
}