using Ant.DbExpressions;
using System;
using Ant.Utility;
using Ant.Descriptors;
using Ant.ORM;

namespace Ant.Query.QueryState
{
    internal sealed class RootQueryState : QueryStateBase
    {
        Type _elementType;
        public RootQueryState(Type elementType)
            : base(CreateResultElement(elementType))
        {
            this._elementType = elementType;
        }

        public override FromQueryResult ToFromQueryResult()
        {
            if (this.Result.Condition == null)
            {
                FromQueryResult result = new FromQueryResult();
                result.FromTable = this.Result.FromTable;
                result.MappingObjectExpression = this.Result.MappingObjectExpression;
                return result;
            }

            return base.ToFromQueryResult();
        }
        /// <summary>
        /// 创建结果元素
        /// </summary>
        /// <param name="type"></param>
        /// <returns></returns>
        static ResultElement CreateResultElement(Type type)
        {
            //TODO init _resultElement
            ResultElement resultElement = new ResultElement();
            MetaData typeDescriptor = new MetaData();
             typeDescriptor.FiledMeta = MetaDataManager.GetMetaData(type);//获取实体元素

            string alias = resultElement.GenerateUniqueTableAlias(typeDescriptor.FiledMeta.Table.Name);

            resultElement.FromTable = CreateRootTable(typeDescriptor.FiledMeta.Table, alias);
            MappingObjectExpression moe = new MappingObjectExpression(typeDescriptor.FiledMeta.EntityType.GetConstructor(Type.EmptyTypes));

            DbTableSegment tableExp = resultElement.FromTable.Table;
            DbTable table = new DbTable(alias);

            foreach (var item in typeDescriptor.FiledMeta.MemberColumnMap)//遍历实体的所有元素
            {
                moe.AddMemberExpression(item.Key, item.Value);
                if (item.Key.Name.ToLower() == typeDescriptor.FiledMeta.PrimaryKey.Column.Name.ToLower())
                    moe.PrimaryKey = item.Value;
            }

            resultElement.MappingObjectExpression = moe;

            return resultElement;
        }
        /// <summary>
        /// 
        /// </summary>
        /// <param name="table"></param>
        /// <param name="alias"></param>
        /// <returns></returns>
        static DbFromTableExpression CreateRootTable(DbTable table, string alias)
        {
            DbTableExpression tableExp = new DbTableExpression(table);
            DbTableSegment tableSeg = new DbTableSegment(tableExp, alias);
            var fromTableExp = new DbFromTableExpression(tableSeg);
            return fromTableExp;
        }
    }
}