using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Runtime.Loader;
using System.Text;
using System.Threading.Tasks;

namespace Plugin
{
 /// <summary>
 /// 程序集加载器
 /// <seealso cref="http://t.zoukankan.com/Leo_wl-p-15708371.html"/>
 /// <seealso cref="https://www.1024sky.cn/blog/article/53738"/>
 /// </summary>
 public class AssemblyLoader
 {
 private string _basePath;
 private AssemblyLoadContext context;

 public AssemblyLoader(string basePath)
 {
 _basePath = basePath;
 }
 /// <summary> 
 /// 加载程序集 
 /// </summary> 
 /// <param name="dllFileName"></param> 
 /// <returns></returns> 
 public Assembly LoadAssembly(string dllFileName)
 {
 context = new AssemblyLoadContext(dllFileName);
 context.Resolving += Context_Resolving;
 //需要绝对路径
 string path = Path.Combine(_basePath, dllFileName);
 if (File.Exists(path))
 {
 using (var stream = File.OpenRead(path))
 {
 Assembly assembly = context.LoadFromStream(stream);
 return assembly;
 }
 }
 else
 {
 Console.WriteLine($"加载动态dll失败:{dllFileName}不存在:{path}");
 }
 return null;
 }
 public Type[] Load(string dllFileName)
 {
 var assembly = LoadAssembly(dllFileName);
 if (assembly != null) return assembly.GetTypes();
 return new Type[] { };
 }
 public Type Load(string dllFileName, string typeName)
 {
 return Load(dllFileName).Where(o => o.Name == typeName).FirstOrDefault();
 }

 /// <summary>
 /// 加载依赖文件
 /// </summary>
 /// <param name="context"></param>
 /// <param name="assemblyName"></param>
 /// <returns></returns>
 private Assembly Context_Resolving(AssemblyLoadContext context, AssemblyName assemblyName)
 {
 string expectedPath = Path.Combine(_basePath, assemblyName.Name + ".dll"); ;
 if (File.Exists(expectedPath))
 {
 try
 {
 using (var stream = File.OpenRead(expectedPath))
 {
 return context.LoadFromStream(stream);
 }
 }
 catch (Exception ex)
 {
 Console.WriteLine($"加载节点{expectedPath}发生异常:{ex.Message},{ex.StackTrace}");
 }
 }
 else
 {
 Console.WriteLine($"依赖文件不存在:{expectedPath}");
 }
 return null;
 }
 }
}