Medusa System Added

Read about the medusa system [here](https://nadekobot.readthedocs.io/en/latest/medusa/creating-a-medusa/)

src/NadekoBot/Common/Medusa/MedusaLoaderService.cs

@@ -0,0 +1,880 @@
+using Discord.Commands.Builders;
+using Microsoft.Extensions.DependencyInjection;
+using NadekoBot.Common.ModuleBehaviors;
+using System.Collections.Immutable;
+using System.Diagnostics.CodeAnalysis;
+using System.Globalization;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+
+namespace Nadeko.Medusa;
+
+// ReSharper disable RedundantAssignment
+public sealed class MedusaLoaderService : IMedusaLoaderService, IReadyExecutor, INService
+{
+    private readonly CommandService _cmdService;
+    private readonly IServiceProvider _botServices;
+    private readonly IBehaviorHandler _behHandler;
+    private readonly IPubSub _pubSub;
+    private readonly IMedusaConfigService _medusaConfig;
+    
+    private readonly ConcurrentDictionary<string, ResolvedMedusa> _resolved = new();
+    private readonly SemaphoreSlim _lock = new SemaphoreSlim(1, 1);
+
+    private readonly TypedKey<string> _loadKey = new("medusa:load");
+    private readonly TypedKey<string> _unloadKey = new("medusa:unload");
+    
+    private readonly TypedKey<bool> _stringsReload = new("medusa:reload_strings");
+
+    private const string BASE_DIR = "data/medusae";
+
+    public MedusaLoaderService(CommandService cmdService,
+        IServiceProvider botServices,
+        IBehaviorHandler behHandler,
+        IPubSub pubSub,
+        IMedusaConfigService medusaConfig)
+    {
+        _cmdService = cmdService;
+        _botServices = botServices;
+        _behHandler = behHandler;
+        _pubSub = pubSub;
+        _medusaConfig = medusaConfig;
+        
+        // has to be done this way to support this feature on sharded bots
+        _pubSub.Sub(_loadKey, async name => await InternalLoadAsync(name));
+        _pubSub.Sub(_unloadKey, async name => await InternalUnloadAsync(name));
+
+        _pubSub.Sub(_stringsReload, async _ => await ReloadStringsInternal());
+    }
+
+    public IReadOnlyCollection<string> GetAllMedusae()
+    {
+        if (!Directory.Exists(BASE_DIR))
+            return Array.Empty<string>();
+
+        return Directory.GetDirectories(BASE_DIR)
+                        .Select(x => Path.GetRelativePath(BASE_DIR, x))
+                        .ToArray();
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public IReadOnlyCollection<MedusaStats> GetLoadedMedusae(CultureInfo? culture)
+    {
+        var toReturn = new List<MedusaStats>(_resolved.Count);
+        foreach (var (name, resolvedData) in _resolved)
+        {
+            var sneks = new List<SnekStats>(resolvedData.SnekInfos.Count);
+
+            foreach (var snekInfos in resolvedData.SnekInfos.Concat(resolvedData.SnekInfos.SelectMany(x => x.Subsneks)))
+            {
+                var commands = new List<SnekCommandStats>();
+
+                foreach (var command in snekInfos.Commands)
+                {
+                    commands.Add(new SnekCommandStats(command.Aliases.First()));
+                }
+                
+                sneks.Add(new SnekStats(snekInfos.Name, commands));
+            }
+
+            toReturn.Add(new MedusaStats(name, resolvedData.Strings.GetDescription(culture), sneks));
+        }
+        return toReturn;
+    }
+
+    public async Task OnReadyAsync()
+    {
+        foreach (var name in _medusaConfig.GetLoadedMedusae())
+        {
+            var result = await InternalLoadAsync(name);
+            if(result != MedusaLoadResult.Success)
+                Log.Warning("Unable to load '{MedusaName}' medusa", name);
+            else 
+                Log.Warning("Loaded medusa '{MedusaName}'", name);
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public async Task<MedusaLoadResult> LoadMedusaAsync(string medusaName)
+    {
+        // try loading on this shard first to see if it works
+        var res = await InternalLoadAsync(medusaName);
+        if (res == MedusaLoadResult.Success)
+        {
+            // if it does publish it so that other shards can load the medusa too
+            // this method will be ran twice on this shard but it doesn't matter as 
+            // the second attempt will be ignored
+            await _pubSub.Pub(_loadKey, medusaName);
+        }
+
+        return res;
+    }
+    
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public async Task<MedusaUnloadResult> UnloadMedusaAsync(string medusaName)
+    {
+        var res = await InternalUnloadAsync(medusaName);
+        if (res == MedusaUnloadResult.Success)
+        {
+            await _pubSub.Pub(_unloadKey, medusaName);
+        }
+
+        return res;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public string[] GetCommandExampleArgs(string medusaName, string commandName, CultureInfo culture)
+    {
+        if (!_resolved.TryGetValue(medusaName, out var data))
+            return Array.Empty<string>();
+
+        return data.Strings.GetCommandStrings(commandName, culture).Args
+               ?? data.SnekInfos
+                      .SelectMany(x => x.Commands)
+                      .FirstOrDefault(x => x.Aliases.Any(alias
+                          => alias.Equals(commandName, StringComparison.InvariantCultureIgnoreCase)))
+                      ?.OptionalStrings
+                      .Args
+               ?? new[] { string.Empty };
+    }
+
+    public Task ReloadStrings()
+        => _pubSub.Pub(_stringsReload, true);
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private void ReloadStringsSync()
+    {
+        foreach (var resolved in _resolved.Values)
+        {
+            resolved.Strings.Reload();
+        }
+    }
+    
+    private async Task ReloadStringsInternal()
+    {
+        await _lock.WaitAsync();
+        try
+        {
+            ReloadStringsSync();
+        }
+        finally
+        {
+            _lock.Release();
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public string GetCommandDescription(string medusaName, string commandName, CultureInfo culture)
+    {
+        if (!_resolved.TryGetValue(medusaName, out var data))
+            return string.Empty;
+
+        return data.Strings.GetCommandStrings(commandName, culture).Desc
+               ?? data.SnekInfos
+                      .SelectMany(x => x.Commands)
+                      .FirstOrDefault(x => x.Aliases.Any(alias
+                          => alias.Equals(commandName, StringComparison.InvariantCultureIgnoreCase)))
+                      ?.OptionalStrings
+                      .Desc
+               ?? string.Empty;
+    }
+    
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private async ValueTask<MedusaLoadResult> InternalLoadAsync(string name)
+    {
+        if (_resolved.ContainsKey(name))
+            return MedusaLoadResult.AlreadyLoaded;
+        
+        var safeName = Uri.EscapeDataString(name);
+        name = name.ToLowerInvariant();
+
+        await _lock.WaitAsync();
+        try
+        {
+            var success = LoadAssemblyInternal(safeName,
+                out var ctx,
+                out var snekData,
+                out var services,
+                out var strings,
+                out var typeReaders);
+
+            if (success)
+            {
+                var moduleInfos = new List<ModuleInfo>();
+
+                // todo uncomment
+                LoadTypeReadersInternal(typeReaders);
+
+                foreach (var point in snekData)
+                {
+                    try
+                    {
+                        // initialize snek and subsneks
+                        await point.Instance.InitializeAsync();
+                        foreach (var sub in point.Subsneks)
+                        {
+                            await sub.Instance.InitializeAsync();
+                        }
+
+                        var module = await LoadModuleInternalAsync(name, point, strings, services);
+                        moduleInfos.Add(module);
+                    }
+                    catch (Exception ex)
+                    {
+                        Log.Warning(ex,
+                            "Error loading snek {SnekName}",
+                            point.Name);
+                    }
+                }
+
+                var execs = GetExecsInternal(snekData, strings, services);
+                await _behHandler.AddRangeAsync(execs);
+
+                _resolved[name] = new(LoadContext: ctx,
+                    ModuleInfos: moduleInfos.ToImmutableArray(),
+                    SnekInfos: snekData.ToImmutableArray(),
+                    strings,
+                    typeReaders,
+                    execs)
+                {
+                    Services = services
+                };
+
+                
+                services = null;
+                _medusaConfig.AddLoadedMedusa(safeName);
+                return MedusaLoadResult.Success;
+            }
+
+            return MedusaLoadResult.Empty;
+        }
+        catch (Exception ex) when (ex is FileNotFoundException or BadImageFormatException)
+        {
+            return MedusaLoadResult.NotFound;
+        }
+        catch (Exception ex)
+        {
+            Log.Error(ex, "An error occurred loading a medusa");
+            return MedusaLoadResult.UnknownError;
+        }
+        finally
+        {
+            _lock.Release();
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private IReadOnlyCollection<ICustomBehavior> GetExecsInternal(IReadOnlyCollection<SnekInfo> snekData, IMedusaStrings strings, IServiceProvider services)
+    {
+        var behs = new List<ICustomBehavior>();
+        foreach (var snek in snekData)
+        {
+            behs.Add(new BehaviorAdapter(new(snek.Instance), strings, services));
+
+            foreach (var sub in snek.Subsneks)
+            {
+                behs.Add(new BehaviorAdapter(new(sub.Instance), strings, services));
+            }
+        }
+
+        
+        return behs;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private void LoadTypeReadersInternal(Dictionary<Type, TypeReader> typeReaders)
+    {
+        var notAddedTypeReaders = new List<Type>();
+        foreach (var (type, typeReader) in typeReaders)
+        {
+            // if type reader for this type already exists, it will not be replaced
+            if (_cmdService.TypeReaders.Contains(type))
+            {
+                notAddedTypeReaders.Add(type);
+                continue;
+            }
+    
+            _cmdService.AddTypeReader(type, typeReader);
+        }
+    
+        // remove the ones that were not added
+        // to prevent them from being unloaded later
+        // as they didn't come from this medusa
+        foreach (var toRemove in notAddedTypeReaders)
+        {
+            typeReaders.Remove(toRemove);
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private bool LoadAssemblyInternal(
+        string safeName,
+        [NotNullWhen(true)] out WeakReference<MedusaAssemblyLoadContext>? ctxWr,
+        [NotNullWhen(true)] out IReadOnlyCollection<SnekInfo>? snekData,
+        out IServiceProvider services,
+        out IMedusaStrings strings,
+        out Dictionary<Type, TypeReader> typeReaders)
+    {
+        ctxWr = null;
+        snekData = null;
+        
+        var path = $"{BASE_DIR}/{safeName}/{safeName}.dll";
+        strings = MedusaStrings.CreateDefault($"{BASE_DIR}/{safeName}");
+        var ctx = new MedusaAssemblyLoadContext(Path.GetDirectoryName(path)!);
+        var a = ctx.LoadFromAssemblyPath(Path.GetFullPath(path));
+        var sis = LoadSneksFromAssembly(a, out services);
+        typeReaders = LoadTypeReadersFromAssembly(a, strings, services);
+
+        if (sis.Count == 0)
+        {
+            return false;
+        }
+
+        ctxWr = new(ctx);
+        snekData = sis;
+        
+        return true;
+    }
+
+    private static readonly Type _paramParserType = typeof(ParamParser<>);
+    
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private Dictionary<Type, TypeReader> LoadTypeReadersFromAssembly(
+        Assembly assembly,
+        IMedusaStrings strings,
+        IServiceProvider services)
+    {
+        var paramParsers = assembly.GetExportedTypes()
+                .Where(x => x.IsClass
+                            && !x.IsAbstract
+                            && x.BaseType is not null
+                            && x.BaseType.IsGenericType
+                            && x.BaseType.GetGenericTypeDefinition() == _paramParserType);
+
+        var typeReaders = new Dictionary<Type, TypeReader>();
+        foreach (var parserType in paramParsers)
+        {
+            var parserObj = ActivatorUtilities.CreateInstance(services, parserType);
+
+            var targetType = parserType.BaseType!.GetGenericArguments()[0];
+            var typeReaderInstance = (TypeReader)Activator.CreateInstance(
+                typeof(ParamParserAdapter<>).MakeGenericType(targetType),
+                args: new[] { parserObj, strings, services })!;
+            
+            typeReaders.Add(targetType, typeReaderInstance);
+        }
+
+        return typeReaders;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private async Task<ModuleInfo> LoadModuleInternalAsync(string medusaName, SnekInfo snekInfo, IMedusaStrings strings, IServiceProvider services)
+    {
+        var module = await _cmdService.CreateModuleAsync(snekInfo.Instance.Prefix,
+            CreateModuleFactory(medusaName, snekInfo, strings, services));
+        
+        return module;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private Action<ModuleBuilder> CreateModuleFactory(
+        string medusaName,
+        SnekInfo snekInfo,
+        IMedusaStrings strings,
+        IServiceProvider medusaServices)
+        => mb =>
+        {
+            var m = mb.WithName(snekInfo.Name);
+
+            foreach (var cmd in snekInfo.Commands)
+            {
+                m.AddCommand(cmd.Aliases.First(),
+                    CreateCallback(cmd.ContextType,
+                        new(snekInfo),
+                        new(cmd),
+                        new(medusaServices),
+                        strings),
+                    CreateCommandFactory(medusaName, cmd));
+            }
+
+            foreach (var subInfo in snekInfo.Subsneks)
+                m.AddModule(subInfo.Instance.Prefix, CreateModuleFactory(medusaName, subInfo, strings, medusaServices));
+        };
+
+    private static readonly RequireContextAttribute _reqGuild = new RequireContextAttribute(ContextType.Guild);
+    private static readonly RequireContextAttribute _reqDm = new RequireContextAttribute(ContextType.DM);
+    private Action<CommandBuilder> CreateCommandFactory(string medusaName, SnekCommandData cmd)
+        => (cb) =>
+        {
+            cb.AddAliases(cmd.Aliases.Skip(1).ToArray());
+
+            if (cmd.ContextType == CommandContextType.Guild)
+                cb.AddPrecondition(_reqGuild);
+            else if (cmd.ContextType == CommandContextType.Dm)
+                cb.AddPrecondition(_reqDm);
+
+            cb.WithPriority(cmd.Priority);
+            
+            // using summary to save method name
+            // method name is used to retrieve desc/usages
+            cb.WithRemarks($"medusa///{medusaName}");
+            cb.WithSummary(cmd.MethodInfo.Name.ToLowerInvariant());
+            
+            foreach (var param in cmd.Parameters)
+            {
+                cb.AddParameter(param.Name, param.Type, CreateParamFactory(param));
+            }
+        };
+
+    private Action<ParameterBuilder> CreateParamFactory(ParamData paramData)
+        => (pb) =>
+        {
+            pb.WithIsMultiple(paramData.IsParams)
+              .WithIsOptional(paramData.IsOptional)
+              .WithIsRemainder(paramData.IsLeftover);
+        };
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private Func<ICommandContext, object[], IServiceProvider, CommandInfo, Task> CreateCallback(
+        CommandContextType contextType,
+        WeakReference<SnekInfo> snekDataWr,
+        WeakReference<SnekCommandData> snekCommandDataWr,
+        WeakReference<IServiceProvider> medusaServicesWr,
+        IMedusaStrings strings)
+        => async (context, parameters, svcs, _) =>
+        {
+            if (!snekCommandDataWr.TryGetTarget(out var cmdData)
+                || !snekDataWr.TryGetTarget(out var snekData)
+                || !medusaServicesWr.TryGetTarget(out var medusaServices))
+            {
+                Log.Warning("Attempted to run an unloaded snek's command");
+                return;
+            }
+                
+            var paramObjs = ParamObjs(contextType, cmdData, parameters, context, svcs, medusaServices, strings);
+
+            try
+            {
+                var methodInfo = cmdData.MethodInfo;
+                if (methodInfo.ReturnType == typeof(Task)
+                    || (methodInfo.ReturnType.IsGenericType
+                        && methodInfo.ReturnType.GetGenericTypeDefinition() == typeof(Task<>)))
+                {
+                    await (Task)methodInfo.Invoke(snekData.Instance, paramObjs)!;
+                }
+                else if (methodInfo.ReturnType == typeof(ValueTask))
+                {
+                    await ((ValueTask)methodInfo.Invoke(snekData.Instance, paramObjs)!).AsTask();
+                }
+                else // if (methodInfo.ReturnType == typeof(void))
+                {
+                    methodInfo.Invoke(snekData.Instance, paramObjs);
+                }
+            }
+            finally
+            {
+                paramObjs = null;
+                cmdData = null;
+                
+                snekData = null;
+                medusaServices = null;
+            }
+        };
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static object[] ParamObjs(
+        CommandContextType contextType,
+        SnekCommandData cmdData,
+        object[] parameters,
+        ICommandContext context,
+        IServiceProvider svcs,
+        IServiceProvider svcProvider,
+        IMedusaStrings strings)
+    {
+        var extraParams = contextType == CommandContextType.Unspecified ? 0 : 1;
+        extraParams += cmdData.InjectedParams.Count;
+
+        var paramObjs = new object[parameters.Length + extraParams];
+
+        var startAt = 0;
+        if (contextType != CommandContextType.Unspecified)
+        {
+            paramObjs[0] = ContextAdapterFactory.CreateNew(context, strings, svcs);
+
+            startAt = 1;
+        }
+
+        for (var i = 0; i < cmdData.InjectedParams.Count; i++)
+        {
+            var svc = svcProvider.GetService(cmdData.InjectedParams[i]);
+            if (svc is null)
+            {
+                throw new ArgumentException($"Cannot inject a service of type {cmdData.InjectedParams[i]}");
+            }
+
+            paramObjs[i + startAt] = svc;
+
+            svc = null;
+        }
+
+        startAt += cmdData.InjectedParams.Count;
+
+        for (var i = 0; i < parameters.Length; i++)
+            paramObjs[startAt + i] = parameters[i];
+        
+        return paramObjs;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private async Task<MedusaUnloadResult> InternalUnloadAsync(string name)
+    {
+        name = name.ToLowerInvariant();
+        if (!_resolved.Remove(name, out var lsi))
+            return MedusaUnloadResult.NotLoaded;
+
+        await _lock.WaitAsync();
+        try
+        {
+            UnloadTypeReaders(lsi.TypeReaders);
+
+            foreach (var mi in lsi.ModuleInfos)
+            {
+                await _cmdService.RemoveModuleAsync(mi);
+            }
+
+            await _behHandler.RemoveRangeAsync(lsi.Execs);
+            
+            await DisposeSnekInstances(lsi);
+
+            var lc = lsi.LoadContext;
+
+            // removing this line will prevent assembly from being unloaded quickly
+            // as this local variable will be held for a long time potentially
+            // due to how async works
+            lsi.Services = null!;
+            lsi = null;
+            
+            _medusaConfig.RemoveLoadedMedusa(name);
+            return UnloadInternal(lc)
+                ? MedusaUnloadResult.Success
+                : MedusaUnloadResult.PossiblyUnable;
+        }
+        finally
+        {
+            _lock.Release();
+        }
+    }
+
+    private void UnloadTypeReaders(Dictionary<Type, TypeReader> valueTypeReaders)
+    {
+        foreach (var tr in valueTypeReaders)
+        {
+            _cmdService.TryRemoveTypeReader(tr.Key, false, out _);
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private async Task DisposeSnekInstances(ResolvedMedusa medusa)
+    {
+        foreach (var si in medusa.SnekInfos)
+        {
+            try
+            {
+                await si.Instance.DisposeAsync();
+                foreach (var sub in si.Subsneks)
+                {
+                    await sub.Instance.DisposeAsync();
+                }  
+            }
+            catch (Exception ex)
+            {
+                Log.Warning(ex,
+                    "Failed cleanup of Snek {SnekName}. This medusa might not unload correctly",
+                    si.Instance.Name);
+            }
+        }
+
+        // medusae = null;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private bool UnloadInternal(WeakReference<MedusaAssemblyLoadContext> lsi)
+    {
+        UnloadContext(lsi);
+        GcCleanup();
+
+        return !lsi.TryGetTarget(out _);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private void UnloadContext(WeakReference<MedusaAssemblyLoadContext> lsiLoadContext)
+    {
+        if(lsiLoadContext.TryGetTarget(out var ctx))
+            ctx.Unload();
+    }
+    
+    private void GcCleanup()
+    {
+        // cleanup
+        for (var i = 0; i < 10; i++)
+        {
+            GC.Collect();
+            GC.WaitForPendingFinalizers();
+            GC.WaitForFullGCComplete();
+            GC.Collect();
+        }
+    }
+
+    private static readonly Type _snekType = typeof(Snek);
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private IServiceProvider LoadMedusaServicesInternal(Assembly a)
+        => new ServiceCollection()
+           .Scan(x => x.FromAssemblies(a)
+                       .AddClasses(static x => x.WithAttribute<svcAttribute>(x => x.Lifetime == Lifetime.Transient))
+                       .AsSelfWithInterfaces()
+                       .WithTransientLifetime()
+                       .AddClasses(static x => x.WithAttribute<svcAttribute>(x => x.Lifetime == Lifetime.Singleton))
+                       .AsSelfWithInterfaces()
+                       .WithSingletonLifetime())
+           .BuildServiceProvider();
+
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public IReadOnlyCollection<SnekInfo> LoadSneksFromAssembly(Assembly a, out IServiceProvider services)
+    {
+        var medusaServices = LoadMedusaServicesInternal(a);
+        services = new MedusaServiceProvider(_botServices, medusaServices);
+        
+        // find all types in teh assembly
+        var types = a.GetExportedTypes();
+        // snek is always a public non abstract class
+        var classes = types.Where(static x => x.IsClass
+                                              && (x.IsNestedPublic || x.IsPublic)
+                                              && !x.IsAbstract
+                                              && x.BaseType == _snekType
+                                              && (x.DeclaringType is null || x.DeclaringType.IsAssignableTo(_snekType)))
+                           .ToList();
+
+        var topModules = new Dictionary<Type, SnekInfo>();
+        
+        foreach (var cl in classes)
+        {
+            if (cl.DeclaringType is not null)
+                continue;
+            
+            // get module data, and add it to the topModules dictionary
+            var module = GetModuleData(cl, services);
+            topModules.Add(cl, module);
+        }
+
+        foreach (var c in classes)
+        {
+            if (c.DeclaringType is not Type dt)
+                continue;
+
+            // if there is no top level module which this module is a child of
+            // just print a warning and skip it
+            if (!topModules.TryGetValue(dt, out var parentData))
+            {
+                Log.Warning("Can't load submodule {SubName} because parent module {Name} does not exist",
+                    c.Name,
+                    dt.Name);
+                continue;
+            }
+            
+            GetModuleData(c, services, parentData);
+        }
+
+        return topModules.Values.ToArray();
+    }
+    
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private SnekInfo GetModuleData(Type type, IServiceProvider services, SnekInfo? parentData = null)
+    {
+        var filters = type.GetCustomAttributes<FilterAttribute>(true)
+                          .ToArray();
+        
+        var instance = (Snek)ActivatorUtilities.CreateInstance(services, type);
+        
+        var module = new SnekInfo(instance.Name,
+            parentData,
+            instance,
+            GetCommands(instance, type),
+            filters);
+
+        if (parentData is not null)
+            parentData.Subsneks.Add(module);
+
+        return module;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private IReadOnlyCollection<SnekCommandData> GetCommands(Snek instance, Type type)
+    {
+        var methodInfos = type
+                          .GetMethods(BindingFlags.Instance
+                                      | BindingFlags.DeclaredOnly
+                                      | BindingFlags.Public)
+                          .Where(static x =>
+                          {
+                              if(x.GetCustomAttribute<cmdAttribute>(true) is null)
+                                  return false;
+
+                              if (x.ReturnType.IsGenericType)
+                              {
+                                  var genericType = x.ReturnType.GetGenericTypeDefinition();
+                                  if (genericType == typeof(Task<>))
+                                      return true;
+                              
+                                  // if (genericType == typeof(ValueTask<>))
+                                  //     return true;
+
+                                  Log.Warning("Method {MethodName} has an invalid return type: {ReturnType}",
+                                      x.Name,
+                                      x.ReturnType);
+                                  
+                                  return false;
+                              }
+
+                              var succ = x.ReturnType == typeof(Task)
+                                         || x.ReturnType == typeof(ValueTask)
+                                         || x.ReturnType == typeof(void);
+
+                              if (!succ)
+                              {
+                                  Log.Warning("Method {MethodName} has an invalid return type: {ReturnType}",
+                                      x.Name,
+                                      x.ReturnType);
+                              }
+
+                              return succ;
+                          });
+        
+        
+        var cmds = new List<SnekCommandData>();
+        foreach (var method in methodInfos)
+        {
+            var filters = method.GetCustomAttributes<FilterAttribute>().ToArray();
+            var prio = method.GetCustomAttribute<prioAttribute>()?.Priority ?? 0;
+
+            var paramInfos = method.GetParameters();
+            var cmdParams = new List<ParamData>();
+            var diParams = new List<Type>();
+            var cmdContext = CommandContextType.Unspecified;
+            var canInject = false;
+            for (var paramCounter = 0; paramCounter < paramInfos.Length; paramCounter++)
+            {
+                var pi = paramInfos[paramCounter];
+
+                var paramName = pi.Name ?? "unnamed";
+                var isContext = paramCounter == 0 && pi.ParameterType.IsAssignableTo(typeof(AnyContext));
+
+                var leftoverAttribute = pi.GetCustomAttribute<Nadeko.Snake.leftoverAttribute>(true);
+                var hasDefaultValue = pi.HasDefaultValue;
+                var isLeftover = leftoverAttribute != null;
+                var isParams = pi.GetCustomAttribute<ParamArrayAttribute>() is not null;
+                var paramType = pi.ParameterType;
+                var isInjected = pi.GetCustomAttribute<injectAttribute>(true) is not null;
+
+                if (isContext)
+                {
+                    if (hasDefaultValue || leftoverAttribute != null || isParams)
+                        throw new ArgumentException("IContext parameter cannot be optional, leftover, constant or params. " + GetErrorPath(method, pi));
+
+                    if (paramCounter != 0)
+                        throw new ArgumentException($"IContext parameter has to be first. {GetErrorPath(method, pi)}");
+
+                    canInject = true;
+                    
+                    if (paramType.IsAssignableTo(typeof(GuildContext)))
+                        cmdContext = CommandContextType.Guild;
+                    else if (paramType.IsAssignableTo(typeof(DmContext)))
+                        cmdContext = CommandContextType.Dm;
+                    else
+                        cmdContext = CommandContextType.Any;
+                    
+                    continue;
+                }
+
+                if (isInjected)
+                {
+                    if (!canInject && paramCounter != 0)
+                        throw new ArgumentException($"Parameters marked as [Injected] have to come after IContext");
+
+                    canInject = true;
+                    
+                    diParams.Add(paramType);
+                    continue;
+                }
+
+                canInject = false;
+
+                if (isParams)
+                {
+                    if (hasDefaultValue)
+                        throw new NotSupportedException("Params can't have const values at the moment. "
+                                                        + GetErrorPath(method, pi));
+                    // if it's params, it means it's an array, and i only need a parser for the actual type,
+                    // as the parser will run on each array element, it can't be null
+                    paramType = paramType.GetElementType()!;
+                }
+
+                // leftover can only be the last parameter.
+                if (isLeftover && paramCounter != paramInfos.Length - 1)
+                {
+                    var path = GetErrorPath(method, pi);
+                    Log.Error("Only one parameter can be marked [Leftover] and it has to be the last one. {Path} ",
+                        path);
+                    throw new ArgumentException("Leftover attribute error.");
+                }
+
+                cmdParams.Add(new ParamData(paramType, paramName, hasDefaultValue, isLeftover, isParams));
+            }
+
+
+            var cmdAttribute = method.GetCustomAttribute<cmdAttribute>()!; 
+            var aliases = cmdAttribute.Aliases;
+            if (aliases.Length == 0)
+                aliases = new[] { method.Name.ToLowerInvariant() };
+            
+            cmds.Add(new(
+                aliases,
+                method,
+                instance,
+                filters,
+                cmdContext,
+                diParams,
+                cmdParams,
+                new(cmdAttribute.desc, cmdAttribute.args),
+                prio
+            ));
+        }
+
+        return cmds;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private string GetErrorPath(MethodInfo m, System.Reflection.ParameterInfo pi)
+        => $@"Module: {m.DeclaringType?.Name} 
+Command: {m.Name}
+ParamName: {pi.Name}
+ParamType: {pi.ParameterType.Name}";
+}
+
+public enum MedusaLoadResult
+{
+    Success,
+    NotFound,
+    AlreadyLoaded,
+    Empty,
+    UnknownError,
+}
+
+public enum MedusaUnloadResult
+{
+    Success,
+    NotLoaded,
+    PossiblyUnable,
+    NotFound,
+}