Plugins: Hook System

Almost an exact replica of https://developer.wordpress.org/plugins/hooks/
This will allow plugins to extend specific points in business logic, such as validation, invoice payload changes, etc

BTCPayServer.Abstractions/Contracts/IPluginHookAction.cs

@@ -0,0 +1,10 @@
+using System.Threading.Tasks;
+
+namespace BTCPayServer.Contracts
+{
+    public interface IPluginHookAction
+    {
+        public string Hook { get; }
+        Task Execute(object args);
+    }
+}

BTCPayServer.Abstractions/Contracts/IPluginHookFilter.cs

@@ -0,0 +1,11 @@
+using System.Threading.Tasks;
+
+namespace BTCPayServer.Contracts
+{
+    public interface IPluginHookFilter
+    {
+        public string Hook { get; }
+        
+        Task<object> Execute(object args);
+    }
+}

BTCPayServer.Abstractions/Contracts/IPluginHookService.cs

@@ -0,0 +1,10 @@
+using System.Threading.Tasks;
+
+namespace BTCPayServer.Contracts
+{
+    public interface IPluginHookService
+    {
+        Task ApplyAction(string hook, object args);
+        Task<object> ApplyFilter(string hook, object args);
+    }
+}

BTCPayServer.Abstractions/Contracts/IUIExtension.cs

@@ -0,0 +1,9 @@
+namespace BTCPayServer.Contracts
+{
+    public interface IUIExtension
+    {
+        string Partial { get; }
+        
+        string Location { get; }
+    }
+}

BTCPayServer.Abstractions/Contracts/PluginAction.cs

@@ -0,0 +1,15 @@
+using System.Threading.Tasks;
+
+namespace BTCPayServer.Contracts
+{
+    public abstract class PluginAction<T>:IPluginHookAction
+    {
+        public string Hook { get; }
+        public Task Execute(object args)
+        {
+            return Execute(args is T args1 ? args1 : default);
+        }
+
+        public abstract Task Execute(T arg);
+    }
+}

BTCPayServer.Abstractions/Contracts/PluginHookFilter.cs

@@ -0,0 +1,15 @@
+using System.Threading.Tasks;
+
+namespace BTCPayServer.Contracts
+{
+    public abstract class PluginHookFilter<T>:IPluginHookFilter
+    {
+        public string Hook { get; }
+        public Task<object> Execute(object args)
+        {
+            return Execute(args is T args1 ? args1 : default).ContinueWith(task => task.Result as object);
+        }
+
+        public abstract Task<T> Execute(T arg);
+    }
+}

BTCPayServer.Abstractions/Contracts/UIExtension.cs

@@ -1,12 +1,5 @@
 namespace BTCPayServer.Contracts
 {
-    public interface IUIExtension
-    {
-        string Partial { get; }
-        
-        string Location { get; }
-    }
-
     public class UIExtension: IUIExtension
     {
         public UIExtension(string partial, string location)

BTCPayServer/Hosting/BTCPayServerServices.cs

@@ -149,6 +149,7 @@ namespace BTCPayServer.Hosting
 
             services.TryAddSingleton<AppService>();
             services.AddSingleton<PluginService>();
+            services.AddSingleton<IPluginHookService>(provider => provider.GetService<PluginService>());
             services.TryAddTransient<Safe>();
             services.TryAddSingleton<Ganss.XSS.HtmlSanitizer>(o =>
             {

BTCPayServer/Plugins/PluginService.cs

@@ -15,18 +15,21 @@ using Newtonsoft.Json;
 
 namespace BTCPayServer.Plugins
 {
-    public class PluginService
+    public class PluginService: IPluginHookService
     {
         private readonly BTCPayServerOptions _btcPayServerOptions;
         private readonly HttpClient _githubClient;
-
+        private readonly IEnumerable<IPluginHookAction> _actions;
+        private readonly IEnumerable<IPluginHookFilter> _filters;
         public PluginService(IEnumerable<IBTCPayServerPlugin> btcPayServerPlugins,
-            IHttpClientFactory httpClientFactory, BTCPayServerOptions btcPayServerOptions)
+            IHttpClientFactory httpClientFactory, BTCPayServerOptions btcPayServerOptions,IEnumerable<IPluginHookAction> actions, IEnumerable<IPluginHookFilter> filters)
         {
             LoadedPlugins = btcPayServerPlugins;
             _githubClient = httpClientFactory.CreateClient();
             _githubClient.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("btcpayserver", "1"));
             _btcPayServerOptions = btcPayServerOptions;
+            _actions = actions;
+            _filters = filters;
         }
 
         public IEnumerable<IBTCPayServerPlugin> LoadedPlugins { get; }
@@ -128,5 +131,27 @@ namespace BTCPayServer.Plugins
         {
             PluginManager.CancelCommands(_btcPayServerOptions.PluginDir, plugin);
         }
+        
+        public async Task ApplyAction(string hook, object args)
+        {
+            var filters = _actions
+                .Where(filter => filter.Hook.Equals(hook, StringComparison.InvariantCultureIgnoreCase)).ToList();
+            foreach (IPluginHookAction pluginHookFilter in filters)
+            {
+                await pluginHookFilter.Execute(args);
+            }
+        }
+
+        public async Task<object> ApplyFilter(string hook, object args)
+        {
+            var filters = _filters
+                .Where(filter => filter.Hook.Equals(hook, StringComparison.InvariantCultureIgnoreCase)).ToList();
+            foreach (IPluginHookFilter pluginHookFilter in filters)
+            {
+                args = await pluginHookFilter.Execute(args);
+            }
+
+            return args;
+        }
     }
 }