using System;
using System.Collections.Generic;
using System.Linq;
using NewLife;
using NewLife.Reflection;

namespace XCode
{
    /// <summary>用于指定数据属性映射关系</summary>
    [AttributeUsage(AttributeTargets.Property)]
    public class MapAttribute : Attribute
    {
        #region 属性
        /// <summary>数据列</summary>
        public String Name { get; set; }

        private MapProvider _Provider;
        /// <summary>目标提供者</summary>
        public MapProvider Provider { get { return _Provider ??= GetProvider(_Type, _Key); } set { _Provider = value; } }
        #endregion

        #region 构造
        /// <summary>指定一个表内关联关系</summary>
        /// <param name="column"></param>
        public MapAttribute(String column)
        {
            Name = column;
        }

        /// <summary>指定一个关系</summary>
        /// <param name="name"></param>
        /// <param name="type"></param>
        /// <param name="key"></param>
        public MapAttribute(String name, Type type, String key = null)
        {
            Name = name;
            _Type = type;
            _Key = key;
        }
        #endregion

        #region 方法
        private readonly Type _Type;
        private readonly String _Key;

        private MapProvider GetProvider(Type type, String key)
        {
            if (type == null) return null;

            // 区分实体类和提供者
            if (type.As<MapProvider>()) return Activator.CreateInstance(type) as MapProvider;

            if (key.IsNullOrEmpty()) key = type.AsFactory()?.Unique?.Name;
            return new MapProvider { EntityType = type, Key = key };
        }
        #endregion
    }

    /// <summary>映射提供者</summary>
    public class MapProvider
    {
        #region 属性
        /// <summary>实体类型</summary>
        public Type EntityType { get; set; }

        /// <summary>关联键</summary>
        public String Key { get; set; }
        #endregion

        #region 方法
        /// <summary>获取数据源</summary>
        /// <returns></returns>
        public virtual IDictionary<Object, String> GetDataSource()
        {
            var fact = EntityType.AsFactory();

            var key = Key;
            var mst = fact.Master?.Name;

            if (key.IsNullOrEmpty()) throw new ArgumentNullException("没有设置关联键", nameof(Key));
            if (mst.IsNullOrEmpty()) throw new ArgumentNullException("没有设置主要字段");

            // 数据较少时，从缓存读取
            var list = fact.Session.Count < 1000 ? fact.FindAllWithCache() : fact.FindAll("", null, null, 0, 100);

            return list.Where(e => e[key] != null).ToDictionary(e => e[key], e => e[mst] + "");
        }
        #endregion
    }
}