using System;
using System.Collections.Generic;
using System.Text;
using System.Reflection.Emit;
using System.Reflection;
using Ant.ORM.Table;

namespace Ant.ORM.Tool
{
    /// <summary>
    /// 快速转换类[数据量越大[500条起],性能越高]
    /// </summary>
    internal class FastToT<T>
    {
        public delegate T EmitHandle(MDataRow row);
        /// <summary>
        /// 构建一个ORM实体转换器
        /// </summary>
        /// <typeparam name="T">转换的目标类型</typeparam>
        /// <param name="schema">表数据架构</param>
        public static EmitHandle Create(MDataTable schema)
        {
            Type tType = typeof(T);
            Type rowType = typeof(MDataRow);
            DynamicMethod method = new DynamicMethod("RowToT", tType, new Type[] { rowType }, tType);

            MethodInfo getValue = rowType.GetMethod("GetItemValue", BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic, null, new Type[] { typeof(int) }, null);


            ILGenerator gen = method.GetILGenerator();
            
            gen.DeclareLocal(tType);
            gen.DeclareLocal(typeof(object));
            gen.DeclareLocal(typeof(bool));

            gen.Emit(OpCodes.Newobj, tType.GetConstructor(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic, null, new Type[] { }, null));
            gen.Emit(OpCodes.Stloc_0);
            int ordinal = -1;

            foreach (FieldInfo field in tType.GetFields(BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public))
            {
                string fieldName = field.Name.TrimStart('_');
                ordinal = schema.GetOrdinal(fieldName);
                if (ordinal > -1)
                {
                    Label retFalse = gen.DefineLabel();
                    gen.Emit(OpCodes.Ldarg_0);
                    gen.Emit(OpCodes.Ldc_I4, ordinal);
                    gen.Emit(OpCodes.Call, getValue);
                    gen.Emit(OpCodes.Stloc_1);

                    gen.Emit(OpCodes.Ldloc_1);
                    gen.Emit(OpCodes.Ldnull);
                    gen.Emit(OpCodes.Ceq);
                    gen.Emit(OpCodes.Stloc_2);
                    gen.Emit(OpCodes.Ldloc_2);

                    gen.Emit(OpCodes.Brtrue_S, retFalse);//为null值，跳过

                    gen.Emit(OpCodes.Ldloc_0);
                    gen.Emit(OpCodes.Ldloc_1);
                    EmitCastObj(gen, field.FieldType);
                    gen.Emit(OpCodes.Stfld, field);

                    gen.MarkLabel(retFalse);//继续下一个循环
                }
            }

            gen.Emit(OpCodes.Ldloc_0);
            gen.Emit(OpCodes.Ret);

            return method.CreateDelegate(typeof(EmitHandle)) as EmitHandle;
        }

        private static void EmitCastObj(ILGenerator il, Type targetType)
        {
            if (targetType.IsValueType)
            {
                il.Emit(OpCodes.Unbox_Any, targetType);
            }
            else
            {
                il.Emit(OpCodes.Castclass, targetType);
            }
        }
    }
}