using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;
using System.Text;
using System.Threading;

namespace EmitCreateDynamicProxy
{
    public class DynamicProxyGenerator
    {

        private const string DynamicAssemblyName = "DynamicAssembly";//动态程序集名称
        private const string DynamicModuleName = "DynamicAssemblyModule";
        private const string DynamicModuleDllName = "DynamicAssembly.dll";//动态模块名称
        private const string ProxyClassNameFormater = "{0}Proxy";
        private const string ModifiedPropertyNamesFieldName = "ModifiedPropertyNames";
        private const MethodAttributes GetSetMethodAttributes = MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.CheckAccessOnOverride | MethodAttributes.Virtual | MethodAttributes.HideBySig;

        /// <summary>
        /// 创建动态程序集,返回AssemblyBuilder
        /// </summary>
        /// <param name="isSavaDll"></param>
        /// <returns></returns>
        private static AssemblyBuilder DefineDynamicAssembly(bool isSavaDll = false)
        {
            //动态创建程序集
            AssemblyName DemoName = new AssemblyName(DynamicAssemblyName);
            AssemblyBuilderAccess assemblyBuilderAccess = isSavaDll ? AssemblyBuilderAccess.RunAndSave : AssemblyBuilderAccess.Run;
            AssemblyBuilder dynamicAssembly = AppDomain.CurrentDomain.DefineDynamicAssembly(DemoName, assemblyBuilderAccess);
            return dynamicAssembly;
        }

        /// <summary>
        /// 创建动态模块,返回ModuleBuilder
        /// </summary>
        /// <param name="isSavaDll"></param>
        /// <returns>ModuleBuilder</returns>
        private static ModuleBuilder DefineDynamicModule(AssemblyBuilder dynamicAssembly, bool isSavaDll = false)
        {
            ModuleBuilder moduleBuilder = null;
            //动态创建模块
            if (isSavaDll)
                moduleBuilder = dynamicAssembly.DefineDynamicModule(DynamicModuleName, DynamicModuleDllName);
            else
                moduleBuilder = dynamicAssembly.DefineDynamicModule(DynamicModuleName);
            return moduleBuilder;
        }

        /// <summary>
        /// 创建动态代理类,重写属性Get Set 方法,并监控属性的Set方法,把变更的属性名加入到list集合中,需要监控的属性必须是virtual
        /// 如果你想保存修改的属性名和属性值,修改Set方法的IL实现
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="isSavaDynamicModule"></param>
        /// <returns></returns>
        public static T CreateDynamicProxy<T>(bool isSavaDynamicModule = false)
        {
            Type modifiedPropertyNamesType = typeof(HashSet<string>);

            Type typeNeedProxy = typeof(T);
            AssemblyBuilder assemblyBuilder = DefineDynamicAssembly(isSavaDynamicModule);
            //动态创建模块
            ModuleBuilder moduleBuilder = DefineDynamicModule(assemblyBuilder, isSavaDynamicModule);
            string proxyClassName = string.Format(ProxyClassNameFormater, typeNeedProxy.Name);
            //动态创建类代理
            TypeBuilder typeBuilderProxy = moduleBuilder.DefineType(proxyClassName, TypeAttributes.Public, typeNeedProxy);
            //定义一个变量存放属性变更名
            FieldBuilder fbModifiedPropertyNames = typeBuilderProxy.DefineField(ModifiedPropertyNamesFieldName, modifiedPropertyNamesType, FieldAttributes.Public);
            //定义接口
            var pt = typeof(PropertyChangedEventHandler);
            typeBuilderProxy.AddInterfaceImplementation(typeof(INotifyPropertyChanged));
            var eil = typeBuilderProxy.DefineEvent("PropertyChanged", EventAttributes.None, typeof(PropertyChangedEventHandler));

            //add field
            var eb = typeBuilderProxy.DefineField("PropertyChanged", typeof(PropertyChangedEventHandler), FieldAttributes.Private);

            var compareExchange = GetGenericMethod(typeof(Interlocked), "CompareExchange");// finds the correct method to call.
                                                                                           // thanks to @marc, create the specific method with the correct type
            compareExchange = compareExchange.MakeGenericMethod(typeof(PropertyChangedEventHandler));

            //add methoed
            var mas = MethodAttributes.Public | MethodAttributes.HideBySig
                | MethodAttributes.NewSlot | MethodAttributes.SpecialName | MethodAttributes.Virtual | MethodAttributes.Final;
            var mb = typeBuilderProxy.DefineMethod("add_PropertyChanged", mas, typeof(void), new Type[] { pt });
            mb.DefineParameter(0, ParameterAttributes.Retval, null);
            mb.DefineParameter(1, ParameterAttributes.In, "value");
            var il = mb.GetILGenerator();
            il.DeclareLocal(pt);
            il.DeclareLocal(pt);
            il.DeclareLocal(pt);
            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Ldfld, eb);
            il.Emit(OpCodes.Stloc_0);
            var lable = il.DefineLabel();
            il.MarkLabel(lable);
            il.Emit(OpCodes.Ldloc_0);
            il.Emit(OpCodes.Stloc_1);
            il.Emit(OpCodes.Ldloc_1);
            il.Emit(OpCodes.Ldarg_1);
            il.Emit(OpCodes.Call, typeof(Delegate).GetMethod("Combine", new Type[] { typeof(Delegate), typeof(Delegate) }));
            il.Emit(OpCodes.Castclass, typeof(PropertyChangedEventHandler));
            il.Emit(OpCodes.Stloc_2);
            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Ldflda, eb);
            il.Emit(OpCodes.Ldloc_2);
            il.Emit(OpCodes.Ldloc_1);
            il.Emit(OpCodes.Call, compareExchange);
            il.Emit(OpCodes.Stloc_0);
            il.Emit(OpCodes.Ldloc_0);
            il.Emit(OpCodes.Ldloc_1);
            il.Emit(OpCodes.Bne_Un_S, lable);
            il.Emit(OpCodes.Ret);

            //remove event
            mb = typeBuilderProxy.DefineMethod("remove_PropertyChanged", mas, typeof(void), new Type[] { pt });
            mb.DefineParameter(0, ParameterAttributes.Retval, null);
            mb.DefineParameter(1, ParameterAttributes.In, "value");

            il = mb.GetILGenerator();
            il.DeclareLocal(pt);
            il.DeclareLocal(pt);
            il.DeclareLocal(pt);
            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Ldfld, eb);
            il.Emit(OpCodes.Stloc_0);
            lable = il.DefineLabel();
            il.MarkLabel(lable);
            il.Emit(OpCodes.Ldloc_0);
            il.Emit(OpCodes.Stloc_1);
            il.Emit(OpCodes.Ldloc_1);
            il.Emit(OpCodes.Ldarg_1);
            il.Emit(OpCodes.Call, typeof(Delegate).GetMethod("Remove", new Type[] { typeof(Delegate), typeof(Delegate) }));
            il.Emit(OpCodes.Castclass, typeof(PropertyChangedEventHandler));
            il.Emit(OpCodes.Stloc_2);
            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Ldflda, eb);
            il.Emit(OpCodes.Ldloc_2);
            il.Emit(OpCodes.Ldloc_1);
            il.Emit(OpCodes.Call, compareExchange);
            il.Emit(OpCodes.Stloc_0);
            il.Emit(OpCodes.Ldloc_0);
            il.Emit(OpCodes.Ldloc_1);
            il.Emit(OpCodes.Bne_Un_S, lable);
            il.Emit(OpCodes.Ret);

            /*
             * 构造函数 实例化 ModifiedPropertyNames,生成类似于下面的代码
               ModifiedPropertyNames = new List<string>();
            */
            ConstructorBuilder constructorBuilder = typeBuilderProxy.DefineConstructor(MethodAttributes.Public, CallingConventions.Standard, null);
            ILGenerator ilgCtor = constructorBuilder.GetILGenerator();
            ilgCtor.Emit(OpCodes.Ldarg_0);//加载当前类
            ilgCtor.Emit(OpCodes.Newobj, modifiedPropertyNamesType.GetConstructor(new Type[0]));//实例化对象入栈
            ilgCtor.Emit(OpCodes.Stfld, fbModifiedPropertyNames);//设置fbModifiedPropertyNames值,为刚入栈的实例化对象
            ilgCtor.Emit(OpCodes.Ret);//返回

            //获取被代理对象的所有属性,循环属性进行重写
            PropertyInfo[] properties = typeNeedProxy.GetProperties();
            foreach (PropertyInfo propertyInfo in properties)
            {
                string propertyName = propertyInfo.Name;
                Type typePepropertyInfo = propertyInfo.PropertyType;
                //动态创建字段和属性
                FieldBuilder fieldBuilder = typeBuilderProxy.DefineField("_" + propertyName, typePepropertyInfo, FieldAttributes.Private);
                PropertyBuilder propertyBuilder = typeBuilderProxy.DefineProperty(propertyName, PropertyAttributes.SpecialName, typePepropertyInfo, null);

                //重写属性的Get Set方法
                var methodGet = typeBuilderProxy.DefineMethod("get_" + propertyName, GetSetMethodAttributes, typePepropertyInfo, Type.EmptyTypes);
                var methodSet = typeBuilderProxy.DefineMethod("set_" + propertyName, GetSetMethodAttributes, null, new Type[] { typePepropertyInfo });

                //il of get method
                var ilGetMethod = methodGet.GetILGenerator();
                ilGetMethod.Emit(OpCodes.Ldarg_0);
                ilGetMethod.Emit(OpCodes.Ldfld, fieldBuilder);
                ilGetMethod.Emit(OpCodes.Ret);
                //il of set method
                ILGenerator ilSetMethod = methodSet.GetILGenerator();
                var nullLabel = ilSetMethod.DefineLabel();
                ilSetMethod.Emit(OpCodes.Ldarg_0);
                ilSetMethod.Emit(OpCodes.Ldarg_1);
                ilSetMethod.Emit(OpCodes.Stfld, fieldBuilder);
                ilSetMethod.Emit(OpCodes.Ldarg_0);
                ilSetMethod.Emit(OpCodes.Ldfld, fbModifiedPropertyNames);
                ilSetMethod.Emit(OpCodes.Dup);
                ilSetMethod.Emit(OpCodes.Brtrue_S, nullLabel);
                ilSetMethod.Emit(OpCodes.Pop);
                var retLabel = ilSetMethod.DefineLabel();
                ilSetMethod.Emit(OpCodes.Br_S, retLabel);
                ilSetMethod.MarkLabel(nullLabel);
                ilSetMethod.Emit(OpCodes.Ldarg_0);
                ilSetMethod.Emit(OpCodes.Ldstr, propertyInfo.Name);
                ilSetMethod.Emit(OpCodes.Newobj, typeof(PropertyChangedEventArgs));
                ilSetMethod.Emit(OpCodes.Callvirt, pt.GetMethod("Invoke", new Type[] { typeof(object), typeof(PropertyChangedEventArgs) }));
                ilSetMethod.Emit(OpCodes.Nop);
                il.MarkLabel(retLabel);
                ilSetMethod.Emit(OpCodes.Ret);

                //设置属性的Get Set方法
                propertyBuilder.SetGetMethod(methodGet);
                propertyBuilder.SetSetMethod(methodSet);
            }

            //使用动态类创建类型
            Type proxyClassType = typeBuilderProxy.CreateType();
            //保存动态创建的程序集
            if (isSavaDynamicModule)
                assemblyBuilder.Save(DynamicModuleDllName);
            //创建类实例
            var instance = Activator.CreateInstance(proxyClassType);
            return (T)instance;
        }

        /// <summary>
        /// 获取属性的变更名称,
        /// 此处只检测调用了Set方法的属性,不会检测值是否真的有变
        /// </summary>
        /// <param name="obj"></param>
        /// <returns></returns>
        public static HashSet<string> GetModifiedProperties(object obj)
        {
            FieldInfo fieldInfo = obj.GetType().GetField(ModifiedPropertyNamesFieldName);
            if (fieldInfo == null) return null;
            object value = fieldInfo.GetValue(obj);
            return value as HashSet<string>;
        }

        private static MethodInfo GetGenericMethod(Type type, string methodName)
        {
            var q = from m in type.GetMethods()
                    where m.Name == methodName && m.IsGenericMethod
                    select m;
            return q.FirstOrDefault();
        }
    }
}