Implement service locator

Dalamud/Service{T}.cs

@@ -0,0 +1,122 @@
+using System;
+using System.Reflection;
+
+using Dalamud.IoC;
+using Dalamud.IoC.Internal;
+using Dalamud.Logging.Internal;
+
+namespace Dalamud
+{
+    /// <summary>
+    /// Basic service locator.
+    /// </summary>
+    /// <remarks>
+    /// Only used internally within Dalamud, if plugins need access to things it should be _only_ via DI.
+    /// </remarks>
+    /// <typeparam name="T">The class you want to store in the service locator.</typeparam>
+    internal static class Service<T> where T : class
+    {
+        private static readonly ModuleLog Log = new("SVC");
+
+        private static T? instance;
+
+        static Service()
+        {
+        }
+
+        /// <summary>
+        /// Sets the type in the service locator to the given object.
+        /// </summary>
+        /// <param name="obj">Object to set.</param>
+        /// <returns>The set object.</returns>
+        public static T Set(T obj)
+        {
+            SetInstanceObject(obj);
+
+            return instance!;
+        }
+
+        /// <summary>
+        /// Sets the type in the service locator via the default parameterless constructor.
+        /// </summary>
+        /// <returns>The set object.</returns>
+        public static T Set()
+        {
+            var obj = (T?)Activator.CreateInstance(typeof(T), true);
+
+            SetInstanceObject(obj);
+
+            return instance!;
+        }
+
+        /// <summary>
+        /// Sets a type in the service locator via a constructor with the given parameter types.
+        /// </summary>
+        /// <param name="args">Constructor arguments.</param>
+        /// <returns>The set object.</returns>
+        public static T Set(params object[] args)
+        {
+            if (args == null)
+            {
+                throw new ArgumentNullException(nameof(args), $"Service locator was passed a null for type {typeof(T).FullName} parameterized constructor ");
+            }
+
+            var flags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.CreateInstance | BindingFlags.OptionalParamBinding;
+            var obj = (T?)Activator.CreateInstance(typeof(T), flags, null, args, null, null);
+
+            SetInstanceObject(obj);
+
+            return obj;
+        }
+
+        /// <summary>
+        /// Attempt to pull the instance out of the service locator.
+        /// </summary>
+        /// <returns>The object if registered.</returns>
+        /// <exception cref="InvalidOperationException">Thrown when the object instance is not present in the service locator.</exception>
+        public static T Get()
+        {
+            return instance ?? throw new InvalidOperationException($"{typeof(T).FullName} has not been registered in the service locator!");
+        }
+
+        /// <summary>
+        /// Attempt to pull the instance out of the service locator.
+        /// </summary>
+        /// <returns>The object if registered, null otherwise.</returns>
+        public static T? GetNullable()
+        {
+            return instance;
+        }
+
+        private static void SetInstanceObject(T instance)
+        {
+            Service<T>.instance = instance ?? throw new ArgumentNullException(nameof(instance), $"Service locator received a null for type {typeof(T).FullName}");
+
+            var availableToPlugins = RegisterInIoCContainer(instance);
+
+            if (availableToPlugins)
+                Log.Information($"Registered {typeof(T).FullName} into service locator and exposed to plugins");
+            else
+                Log.Information($"Registered {typeof(T).FullName} into service locator privately");
+        }
+
+        private static bool RegisterInIoCContainer(T instance)
+        {
+            var attr = typeof(T).GetCustomAttribute<PluginInterfaceAttribute>();
+            if (attr == null)
+            {
+                return false;
+            }
+
+            var ioc = Service<ServiceContainer>.GetNullable();
+            if (ioc == null)
+            {
+                return false;
+            }
+
+            ioc.RegisterSingleton(instance);
+
+            return true;
+        }
+    }
+}