Merge branch 'feature/mod-provided-apis' into develop

15 files changed, 349 insertions, 106 deletions

diff --git a/src/SMAPI.Mods.ConsoleCommands/StardewModdingAPI.Mods.ConsoleCommands.csproj b/src/SMAPI.Mods.ConsoleCommands/StardewModdingAPI.Mods.ConsoleCommands.csproj
index f228bb25..a65ad72c 100644
--- a/src/SMAPI.Mods.ConsoleCommands/StardewModdingAPI.Mods.ConsoleCommands.csproj
+++ b/src/SMAPI.Mods.ConsoleCommands/StardewModdingAPI.Mods.ConsoleCommands.csproj
@@ -41,10 +41,6 @@
       <Private>False</Private>
     </Reference>
     <Reference Include="System" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.Xml.Linq" />
-    <Reference Include="Microsoft.CSharp" />
-    <Reference Include="System.Data" />
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
diff --git a/src/SMAPI/Events/GameEvents.cs b/src/SMAPI/Events/GameEvents.cs
index b477376e..3466470d 100644
--- a/src/SMAPI/Events/GameEvents.cs
+++ b/src/SMAPI/Events/GameEvents.cs
@@ -33,6 +33,9 @@ namespace StardewModdingAPI.Events
         /// <summary>Raised every 60th tick (≈once per second).</summary>
         public static event EventHandler OneSecondTick;
 
+        /// <summary>Raised once after the game initialises and all <see cref="IMod.Entry"/> methods have been called.</summary>
+        public static event EventHandler FirstUpdateTick;
+
 
         /*********
         ** Internal methods
@@ -92,5 +95,12 @@ namespace StardewModdingAPI.Events
         {
             monitor.SafelyRaisePlainEvent($"{nameof(GameEvents)}.{nameof(GameEvents.OneSecondTick)}", GameEvents.OneSecondTick?.GetInvocationList());
         }
+
+        /// <summary>Raise a <see cref="FirstUpdateTick"/> event.</summary>
+        /// <param name="monitor">Encapsulates monitoring and logging.</param>
+        internal static void InvokeFirstUpdateTick(IMonitor monitor)
+        {
+            monitor.SafelyRaisePlainEvent($"{nameof(GameEvents)}.{nameof(GameEvents.FirstUpdateTick)}", GameEvents.FirstUpdateTick?.GetInvocationList());
+        }
     }
 }
diff --git a/src/SMAPI/Framework/DeprecationManager.cs b/src/SMAPI/Framework/DeprecationManager.cs
index 20bb0d2d..7a824a05 100644
--- a/src/SMAPI/Framework/DeprecationManager.cs
+++ b/src/SMAPI/Framework/DeprecationManager.cs
@@ -37,7 +37,7 @@ namespace StardewModdingAPI.Framework
         /// <param name="severity">How deprecated the code is.</param>
         public void Warn(string nounPhrase, string version, DeprecationLevel severity)
         {
-            this.Warn(this.ModRegistry.GetModFromStack(), nounPhrase, version, severity);
+            this.Warn(this.ModRegistry.GetFromStack()?.DisplayName, nounPhrase, version, severity);
         }
 
         /// <summary>Log a deprecation warning.</summary>
@@ -82,7 +82,7 @@ namespace StardewModdingAPI.Framework
         /// <returns>Returns whether the deprecation was successfully marked as warned. Returns <c>false</c> if it was already marked.</returns>
         public bool MarkWarned(string nounPhrase, string version)
         {
-            return this.MarkWarned(this.ModRegistry.GetModFromStack(), nounPhrase, version);
+            return this.MarkWarned(this.ModRegistry.GetFromStack()?.DisplayName, nounPhrase, version);
         }
 
         /// <summary>Mark a deprecation warning as already logged.</summary>
diff --git a/src/SMAPI/Framework/IModMetadata.cs b/src/SMAPI/Framework/IModMetadata.cs
index c21734a7..a36994fd 100644
--- a/src/SMAPI/Framework/IModMetadata.cs
+++ b/src/SMAPI/Framework/IModMetadata.cs
@@ -30,6 +30,9 @@ namespace StardewModdingAPI.Framework
         /// <summary>The mod instance (if it was loaded).</summary>
         IMod Mod { get; }
 
+        /// <summary>The mod-provided API (if any).</summary>
+        object Api { get; }
+
 
         /*********
         ** Public methods
@@ -43,5 +46,9 @@ namespace StardewModdingAPI.Framework
         /// <summary>Set the mod instance.</summary>
         /// <param name="mod">The mod instance to set.</param>
         IModMetadata SetMod(IMod mod);
+
+        /// <summary>Set the mod-provided API instance.</summary>
+        /// <param name="api">The mod-provided API.</param>
+        IModMetadata SetApi(object api);
     }
 }
diff --git a/src/SMAPI/Framework/ModHelpers/ModRegistryHelper.cs b/src/SMAPI/Framework/ModHelpers/ModRegistryHelper.cs
index 9e824694..ea0dbb38 100644
--- a/src/SMAPI/Framework/ModHelpers/ModRegistryHelper.cs
+++ b/src/SMAPI/Framework/ModHelpers/ModRegistryHelper.cs
@@ -1,4 +1,6 @@
-using System.Collections.Generic;
+using System.Collections.Generic;
+using System.Linq;
+using StardewModdingAPI.Framework.Reflection;
 
 namespace StardewModdingAPI.Framework.ModHelpers
 {
@@ -11,6 +13,15 @@ namespace StardewModdingAPI.Framework.ModHelpers
         /// <summary>The underlying mod registry.</summary>
         private readonly ModRegistry Registry;
 
+        /// <summary>Encapsulates monitoring and logging for the mod.</summary>
+        private readonly IMonitor Monitor;
+
+        /// <summary>The mod IDs for APIs accessed by this instanced.</summary>
+        private readonly HashSet<string> AccessedModApis = new HashSet<string>();
+
+        /// <summary>Generates proxy classes to access mod APIs through an arbitrary interface.</summary>
+        private readonly InterfaceProxyBuilder ProxyBuilder;
+
 
         /*********
         ** Public methods
@@ -18,16 +29,20 @@ namespace StardewModdingAPI.Framework.ModHelpers
         /// <summary>Construct an instance.</summary>
         /// <param name="modID">The unique ID of the relevant mod.</param>
         /// <param name="registry">The underlying mod registry.</param>
-        public ModRegistryHelper(string modID, ModRegistry registry)
+        /// <param name="proxyBuilder">Generates proxy classes to access mod APIs through an arbitrary interface.</param>
+        /// <param name="monitor">Encapsulates monitoring and logging for the mod.</param>
+        public ModRegistryHelper(string modID, ModRegistry registry, InterfaceProxyBuilder proxyBuilder, IMonitor monitor)
             : base(modID)
         {
             this.Registry = registry;
+            this.ProxyBuilder = proxyBuilder;
+            this.Monitor = monitor;
         }
 
         /// <summary>Get metadata for all loaded mods.</summary>
         public IEnumerable<IManifest> GetAll()
         {
-            return this.Registry.GetAll();
+            return this.Registry.GetAll().Select(p => p.Manifest);
         }
 
         /// <summary>Get metadata for a loaded mod.</summary>
@@ -35,14 +50,56 @@ namespace StardewModdingAPI.Framework.ModHelpers
         /// <returns>Returns the matching mod's metadata, or <c>null</c> if not found.</returns>
         public IManifest Get(string uniqueID)
         {
-            return this.Registry.Get(uniqueID);
+            return this.Registry.Get(uniqueID)?.Manifest;
         }
 
         /// <summary>Get whether a mod has been loaded.</summary>
         /// <param name="uniqueID">The mod's unique ID.</param>
         public bool IsLoaded(string uniqueID)
         {
-            return this.Registry.IsLoaded(uniqueID);
+            return this.Registry.Get(uniqueID) != null;
+        }
+
+        /// <summary>Get the API provided by a mod, or <c>null</c> if it has none. This signature requires using the <see cref="IModHelper.Reflection"/> API to access the API's properties and methods.</summary>
+        public object GetApi(string uniqueID)
+        {
+            IModMetadata mod = this.Registry.Get(uniqueID);
+            if (mod?.Api != null && this.AccessedModApis.Add(mod.Manifest.UniqueID))
+                this.Monitor.Log($"Accessed mod-provided API for {mod.DisplayName}.", LogLevel.Trace);
+            return mod?.Api;
+        }
+
+        /// <summary>Get the API provided by a mod, mapped to a given interface which specifies the expected properties and methods. If the mod has no API or it's not compatible with the given interface, get <c>null</c>.</summary>
+        /// <typeparam name="TInterface">The interface which matches the properties and methods you intend to access.</typeparam>
+        /// <param name="uniqueID">The mod's unique ID.</param>
+        public TInterface GetApi<TInterface>(string uniqueID) where TInterface : class
+        {
+            // validate
+            if (!this.Registry.AreAllModsInitialised)
+            {
+                this.Monitor.Log("Tried to access a mod-provided API before all mods were initialised.", LogLevel.Error);
+                return null;
+            }
+            if (!typeof(TInterface).IsInterface)
+            {
+                this.Monitor.Log("Tried to map a mod-provided API to a class; must be a public interface.", LogLevel.Error);
+                return null;
+            }
+            if (!typeof(TInterface).IsPublic)
+            {
+                this.Monitor.Log("Tried to map a mod-provided API to a non-public interface; must be a public interface.", LogLevel.Error);
+                return null;
+            }
+
+            // get raw API
+            object api = this.GetApi(uniqueID);
+            if (api == null)
+                return null;
+
+            // get API of type
+            if (api is TInterface castApi)
+                return castApi;
+            return this.ProxyBuilder.CreateProxy<TInterface>(api, this.ModID, uniqueID);
         }
     }
 }
diff --git a/src/SMAPI/Framework/ModLoading/ModMetadata.cs b/src/SMAPI/Framework/ModLoading/ModMetadata.cs
index 5055da75..30fe211b 100644
--- a/src/SMAPI/Framework/ModLoading/ModMetadata.cs
+++ b/src/SMAPI/Framework/ModLoading/ModMetadata.cs
@@ -29,6 +29,9 @@ namespace StardewModdingAPI.Framework.ModLoading
         /// <summary>The mod instance (if it was loaded).</summary>
         public IMod Mod { get; private set; }
 
+        /// <summary>The mod-provided API (if any).</summary>
+        public object Api { get; private set; }
+
 
         /*********
         ** Public methods
@@ -64,5 +67,13 @@ namespace StardewModdingAPI.Framework.ModLoading
             this.Mod = mod;
             return this;
         }
+
+        /// <summary>Set the mod-provided API instance.</summary>
+        /// <param name="api">The mod-provided API.</param>
+        public IModMetadata SetApi(object api)
+        {
+            this.Api = api;
+            return this;
+        }
     }
 }
diff --git a/src/SMAPI/Framework/ModRegistry.cs b/src/SMAPI/Framework/ModRegistry.cs
index 9dde7a20..453d2868 100644
--- a/src/SMAPI/Framework/ModRegistry.cs
+++ b/src/SMAPI/Framework/ModRegistry.cs
@@ -15,26 +15,34 @@ namespace StardewModdingAPI.Framework
         /// <summary>The registered mod data.</summary>
         private readonly List<IModMetadata> Mods = new List<IModMetadata>();
 
-        /// <summary>The friendly mod names treated as deprecation warning sources (assembly full name => mod name).</summary>
-        private readonly IDictionary<string, string> ModNamesByAssembly = new Dictionary<string, string>();
+        /// <summary>An assembly full name => mod lookup.</summary>
+        private readonly IDictionary<string, IModMetadata> ModNamesByAssembly = new Dictionary<string, IModMetadata>();
+
+        /// <summary>Whether all mods have been initialised and their <see cref="IMod.Entry"/> method called.</summary>
+        public bool AreAllModsInitialised { get; set; }
 
 
         /*********
         ** Public methods
         *********/
-        /****
-        ** Basic metadata
-        ****/
+        /// <summary>Register a mod as a possible source of deprecation warnings.</summary>
+        /// <param name="metadata">The mod metadata.</param>
+        public void Add(IModMetadata metadata)
+        {
+            this.Mods.Add(metadata);
+            this.ModNamesByAssembly[metadata.Mod.GetType().Assembly.FullName] = metadata;
+        }
+
         /// <summary>Get metadata for all loaded mods.</summary>
-        public IEnumerable<IManifest> GetAll()
+        public IEnumerable<IModMetadata> GetAll()
         {
-            return this.Mods.Select(p => p.Manifest);
+            return this.Mods.Select(p => p);
         }
 
         /// <summary>Get metadata for a loaded mod.</summary>
         /// <param name="uniqueID">The mod's unique ID.</param>
         /// <returns>Returns the matching mod's metadata, or <c>null</c> if not found.</returns>
-        public IManifest Get(string uniqueID)
+        public IModMetadata Get(string uniqueID)
         {
             // normalise search ID
             if (string.IsNullOrWhiteSpace(uniqueID))
@@ -42,37 +50,13 @@ namespace StardewModdingAPI.Framework
             uniqueID = uniqueID.Trim();
 
             // find match
-            return this.GetAll().FirstOrDefault(p => p.UniqueID.Trim().Equals(uniqueID, StringComparison.InvariantCultureIgnoreCase));
-        }
-
-        /// <summary>Get whether a mod has been loaded.</summary>
-        /// <param name="uniqueID">The mod's unique ID.</param>
-        public bool IsLoaded(string uniqueID)
-        {
-            return this.Get(uniqueID) != null;
-        }
-
-        /****
-        ** Mod data
-        ****/
-        /// <summary>Register a mod as a possible source of deprecation warnings.</summary>
-        /// <param name="metadata">The mod metadata.</param>
-        public void Add(IModMetadata metadata)
-        {
-            this.Mods.Add(metadata);
-            this.ModNamesByAssembly[metadata.Mod.GetType().Assembly.FullName] = metadata.DisplayName;
-        }
-
-        /// <summary>Get all enabled mods.</summary>
-        public IEnumerable<IModMetadata> GetMods()
-        {
-            return (from mod in this.Mods select mod);
+            return this.GetAll().FirstOrDefault(p => p.Manifest.UniqueID.Trim().Equals(uniqueID, StringComparison.InvariantCultureIgnoreCase));
         }
 
-        /// <summary>Get the friendly mod name which defines a type.</summary>
+        /// <summary>Get the mod metadata from one of its assemblies.</summary>
         /// <param name="type">The type to check.</param>
         /// <returns>Returns the mod name, or <c>null</c> if the type isn't part of a known mod.</returns>
-        public string GetModFrom(Type type)
+        public IModMetadata GetFrom(Type type)
         {
             // null
             if (type == null)
@@ -89,7 +73,7 @@ namespace StardewModdingAPI.Framework
 
         /// <summary>Get the friendly name for the closest assembly registered as a source of deprecation warnings.</summary>
         /// <returns>Returns the source name, or <c>null</c> if no registered assemblies were found.</returns>
-        public string GetModFromStack()
+        public IModMetadata GetFromStack()
         {
             // get stack frames
             StackTrace stack = new StackTrace();
@@ -101,9 +85,9 @@ namespace StardewModdingAPI.Framework
             foreach (StackFrame frame in frames)
             {
                 MethodBase method = frame.GetMethod();
-                string name = this.GetModFrom(method.ReflectedType);
-                if (name != null)
-                    return name;
+                IModMetadata mod = this.GetFrom(method.ReflectedType);
+                if (mod != null)
+                    return mod;
             }
 
             // no known assembly found
diff --git a/src/SMAPI/Framework/Reflection/InterfaceProxyBuilder.cs b/src/SMAPI/Framework/Reflection/InterfaceProxyBuilder.cs
new file mode 100644
index 00000000..5abebc18
--- /dev/null
+++ b/src/SMAPI/Framework/Reflection/InterfaceProxyBuilder.cs
@@ -0,0 +1,138 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Reflection.Emit;
+
+namespace StardewModdingAPI.Framework.Reflection
+{
+    /// <summary>Generates proxy classes to access mod APIs through an arbitrary interface.</summary>
+    internal class InterfaceProxyBuilder
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>The CLR module in which to create proxy classes.</summary>
+        private readonly ModuleBuilder ModuleBuilder;
+
+        /// <summary>The generated proxy types.</summary>
+        private readonly IDictionary<string, Type> GeneratedTypes = new Dictionary<string, Type>();
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        public InterfaceProxyBuilder()
+        {
+            AssemblyBuilder assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(new AssemblyName($"StardewModdingAPI.Proxies, Version={this.GetType().Assembly.GetName().Version}, Culture=neutral"), AssemblyBuilderAccess.Run);
+            this.ModuleBuilder = assemblyBuilder.DefineDynamicModule("StardewModdingAPI.Proxies");
+        }
+
+        /// <summary>Create an API proxy.</summary>
+        /// <typeparam name="TInterface">The interface through which to access the API.</typeparam>
+        /// <param name="instance">The API instance to access.</param>
+        /// <param name="sourceModID">The unique ID of the mod consuming the API.</param>
+        /// <param name="targetModID">The unique ID of the mod providing the API.</param>
+        public TInterface CreateProxy<TInterface>(object instance, string sourceModID, string targetModID)
+            where TInterface : class
+        {
+            // validate
+            if (instance == null)
+                throw new InvalidOperationException("Can't proxy access to a null API.");
+            if (!typeof(TInterface).IsInterface)
+                throw new InvalidOperationException("The proxy type must be an interface, not a class.");
+
+            // get proxy type
+            Type targetType = instance.GetType();
+            string proxyTypeName = $"StardewModdingAPI.Proxies.From<{sourceModID}_{typeof(TInterface).FullName}>_To<{targetModID}_{targetType.FullName}>";
+            if (!this.GeneratedTypes.TryGetValue(proxyTypeName, out Type type))
+            {
+                type = this.CreateProxyType(proxyTypeName, typeof(TInterface), targetType);
+                this.GeneratedTypes[proxyTypeName] = type;
+            }
+
+            // create instance
+            ConstructorInfo constructor = type.GetConstructor(new[] { targetType });
+            if (constructor == null)
+                throw new InvalidOperationException($"Couldn't find the constructor for generated proxy type '{proxyTypeName}'."); // should never happen
+            return (TInterface)constructor.Invoke(new[] { instance });
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Define a class which proxies access to a target type through an interface.</summary>
+        /// <param name="proxyTypeName">The name of the proxy type to generate.</param>
+        /// <param name="interfaceType">The interface type through which to access the target.</param>
+        /// <param name="targetType">The target type to access.</param>
+        private Type CreateProxyType(string proxyTypeName, Type interfaceType, Type targetType)
+        {
+            // define proxy type
+            TypeBuilder proxyBuilder = this.ModuleBuilder.DefineType(proxyTypeName, TypeAttributes.Public | TypeAttributes.Class);
+            proxyBuilder.AddInterfaceImplementation(interfaceType);
+
+            // create field to store target instance
+            FieldBuilder field = proxyBuilder.DefineField("__Target", targetType, FieldAttributes.Private);
+
+            // create constructor which accepts target instance
+            {
+                ConstructorBuilder constructor = proxyBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.Standard | CallingConventions.HasThis, new[] { targetType });
+                ILGenerator il = constructor.GetILGenerator();
+
+                il.Emit(OpCodes.Ldarg_0); // this
+                // ReSharper disable once AssignNullToNotNullAttribute -- never null
+                il.Emit(OpCodes.Call, typeof(object).GetConstructor(new Type[0])); // call base constructor
+                il.Emit(OpCodes.Ldarg_0);      // this
+                il.Emit(OpCodes.Ldarg_1);      // load argument
+                il.Emit(OpCodes.Stfld, field); // set field to loaded argument
+                il.Emit(OpCodes.Ret);
+            }
+
+            // proxy methods
+            foreach (MethodInfo proxyMethod in interfaceType.GetMethods())
+            {
+                var targetMethod = targetType.GetMethod(proxyMethod.Name, proxyMethod.GetParameters().Select(a => a.ParameterType).ToArray());
+                if (targetMethod == null)
+                    throw new InvalidOperationException($"The {interfaceType.FullName} interface defines method {proxyMethod.Name} which doesn't exist in the API.");
+
+                this.ProxyMethod(proxyBuilder, targetMethod, field);
+            }
+
+            // create type
+            return proxyBuilder.CreateType();
+        }
+
+        /// <summary>Define a method which proxies access to a method on the target.</summary>
+        /// <param name="proxyBuilder">The proxy type being generated.</param>
+        /// <param name="target">The target method.</param>
+        /// <param name="instanceField">The proxy field containing the API instance.</param>
+        private void ProxyMethod(TypeBuilder proxyBuilder, MethodInfo target, FieldBuilder instanceField)
+        {
+            Type[] argTypes = target.GetParameters().Select(a => a.ParameterType).ToArray();
+
+            // create method
+            MethodBuilder methodBuilder = proxyBuilder.DefineMethod(target.Name, MethodAttributes.Public | MethodAttributes.Final | MethodAttributes.Virtual);
+            methodBuilder.SetParameters(argTypes);
+            methodBuilder.SetReturnType(target.ReturnType);
+
+            // create method body
+            {
+                ILGenerator il = methodBuilder.GetILGenerator();
+
+                // load target instance
+                il.Emit(OpCodes.Ldarg_0);
+                il.Emit(OpCodes.Ldfld, instanceField);
+
+                // invoke target method on instance
+                for (int i = 0; i < argTypes.Length; i++)
+                    il.Emit(OpCodes.Ldarg, i + 1);
+                il.Emit(OpCodes.Call, target);
+
+                // return result
+                il.Emit(OpCodes.Ret);
+            }
+        }
+    }
+}
diff --git a/src/SMAPI/Framework/SGame.cs b/src/SMAPI/Framework/SGame.cs
index e9777e0b..0a614f17 100644
--- a/src/SMAPI/Framework/SGame.cs
+++ b/src/SMAPI/Framework/SGame.cs
@@ -557,9 +557,12 @@ namespace StardewModdingAPI.Framework
                 /*********
                 ** Update events
                 *********/
-                GameEvents.InvokeUpdateTick(this.Monitor);
                 if (this.FirstUpdate)
+                {
                     this.FirstUpdate = false;
+                    GameEvents.InvokeFirstUpdateTick(this.Monitor);
+                }
+                GameEvents.InvokeUpdateTick(this.Monitor);
                 if (this.CurrentUpdateTick % 2 == 0)
                     GameEvents.InvokeSecondUpdateTick(this.Monitor);
                 if (this.CurrentUpdateTick % 4 == 0)
@@ -725,7 +728,7 @@ namespace StardewModdingAPI.Framework
                         }
                         if (Game1.overlayMenu != null)
                         {
-                            Game1.spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, SamplerState.PointClamp, (DepthStencilState) null, (RasterizerState) null);
+                            Game1.spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, SamplerState.PointClamp, (DepthStencilState)null, (RasterizerState)null);
                             Game1.overlayMenu.draw(Game1.spriteBatch);
                             Game1.spriteBatch.End();
                         }
@@ -759,7 +762,7 @@ namespace StardewModdingAPI.Framework
                         }
                         if (Game1.overlayMenu != null)
                         {
-                            Game1.spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, SamplerState.PointClamp, (DepthStencilState) null, (RasterizerState) null);
+                            Game1.spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, SamplerState.PointClamp, (DepthStencilState)null, (RasterizerState)null);
                             Game1.overlayMenu.draw(Game1.spriteBatch);
                             Game1.spriteBatch.End();
                         }
@@ -793,7 +796,7 @@ namespace StardewModdingAPI.Framework
                         }
                         if (Game1.overlayMenu != null)
                         {
-                            Game1.spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, SamplerState.PointClamp, (DepthStencilState) null, (RasterizerState) null);
+                            Game1.spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, SamplerState.PointClamp, (DepthStencilState)null, (RasterizerState)null);
                             Game1.overlayMenu.draw(Game1.spriteBatch);
                             Game1.spriteBatch.End();
                         }
@@ -826,7 +829,7 @@ namespace StardewModdingAPI.Framework
                         }
                         if (Game1.overlayMenu != null)
                         {
-                            Game1.spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, SamplerState.PointClamp, (DepthStencilState) null, (RasterizerState) null);
+                            Game1.spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, SamplerState.PointClamp, (DepthStencilState)null, (RasterizerState)null);
                             Game1.overlayMenu.draw(Game1.spriteBatch);
                             Game1.spriteBatch.End();
                         }
diff --git a/src/SMAPI/IMod.cs b/src/SMAPI/IMod.cs
index 35ac7c0f..44ef32c9 100644
--- a/src/SMAPI/IMod.cs
+++ b/src/SMAPI/IMod.cs
@@ -1,4 +1,4 @@
-namespace StardewModdingAPI
+namespace StardewModdingAPI
 {
     /// <summary>The implementation for a Stardew Valley mod.</summary>
     public interface IMod
@@ -22,5 +22,8 @@
         /// <summary>The mod entry point, called after the mod is first loaded.</summary>
         /// <param name="helper">Provides simplified APIs for writing mods.</param>
         void Entry(IModHelper helper);
+
+        /// <summary>Get an API that other mods can access. This is always called after <see cref="Entry"/>.</summary>
+        object GetApi();
     }
-}
\ No newline at end of file
+}
diff --git a/src/SMAPI/IModRegistry.cs b/src/SMAPI/IModRegistry.cs
index 5ef3fd65..a06e099e 100644
--- a/src/SMAPI/IModRegistry.cs
+++ b/src/SMAPI/IModRegistry.cs
@@ -1,4 +1,4 @@
-using System.Collections.Generic;
+using System.Collections.Generic;
 
 namespace StardewModdingAPI
 {
@@ -16,5 +16,14 @@ namespace StardewModdingAPI
         /// <summary>Get whether a mod has been loaded.</summary>
         /// <param name="uniqueID">The mod's unique ID.</param>
         bool IsLoaded(string uniqueID);
+
+        /// <summary>Get the API provided by a mod, or <c>null</c> if it has none. This signature requires using the <see cref="IModHelper.Reflection"/> API to access the API's properties and methods.</summary>
+        /// <param name="uniqueID">The mod's unique ID.</param>
+        object GetApi(string uniqueID);
+
+        /// <summary>Get the API provided by a mod, mapped to a given interface which specifies the expected properties and methods. If the mod has no API or it's not compatible with the given interface, get <c>null</c>.</summary>
+        /// <typeparam name="TInterface">The interface which matches the properties and methods you intend to access.</typeparam>
+        /// <param name="uniqueID">The mod's unique ID.</param>
+        TInterface GetApi<TInterface>(string uniqueID) where TInterface : class;
     }
-}
\ No newline at end of file
+}
diff --git a/src/SMAPI/Metadata/InstructionMetadata.cs b/src/SMAPI/Metadata/InstructionMetadata.cs
index 3346f1ac..f285764c 100644
--- a/src/SMAPI/Metadata/InstructionMetadata.cs
+++ b/src/SMAPI/Metadata/InstructionMetadata.cs
@@ -50,7 +50,6 @@ namespace StardewModdingAPI.Metadata
                 new EventFinder("StardewModdingAPI.Events.GameEvents", "Initialize", InstructionHandleResult.NotCompatible),
                 new EventFinder("StardewModdingAPI.Events.GameEvents", "LoadContent", InstructionHandleResult.NotCompatible),
                 new EventFinder("StardewModdingAPI.Events.GameEvents", "GameLoaded", InstructionHandleResult.NotCompatible),
-                new EventFinder("StardewModdingAPI.Events.GameEvents", "FirstUpdateTick", InstructionHandleResult.NotCompatible),
                 new EventFinder("StardewModdingAPI.Events.PlayerEvents", "LoadedGame", InstructionHandleResult.NotCompatible),
                 new EventFinder("StardewModdingAPI.Events.PlayerEvents", "FarmerChanged", InstructionHandleResult.NotCompatible),
                 new EventFinder("StardewModdingAPI.Events.TimeEvents", "DayOfMonthChanged", InstructionHandleResult.NotCompatible),
diff --git a/src/SMAPI/Mod.cs b/src/SMAPI/Mod.cs
index ee75ba54..3a753afc 100644
--- a/src/SMAPI/Mod.cs
+++ b/src/SMAPI/Mod.cs
@@ -25,6 +25,9 @@ namespace StardewModdingAPI
         /// <param name="helper">Provides simplified APIs for writing mods.</param>
         public abstract void Entry(IModHelper helper);
 
+        /// <summary>Get an API that other mods can access. This is always called after <see cref="Entry"/>.</summary>
+        public virtual object GetApi() => null;
+
         /// <summary>Release or reset unmanaged resources.</summary>
         public void Dispose()
         {
diff --git a/src/SMAPI/Program.cs b/src/SMAPI/Program.cs
index 8bc2c675..7eda9c66 100644
--- a/src/SMAPI/Program.cs
+++ b/src/SMAPI/Program.cs
@@ -247,7 +247,7 @@ namespace StardewModdingAPI
             this.IsDisposed = true;
 
             // dispose mod data
-            foreach (IModMetadata mod in this.ModRegistry.GetMods())
+            foreach (IModMetadata mod in this.ModRegistry.GetAll())
             {
                 try
                 {
@@ -374,7 +374,7 @@ namespace StardewModdingAPI
             }
 
             // update window titles
-            int modsLoaded = this.ModRegistry.GetMods().Count();
+            int modsLoaded = this.ModRegistry.GetAll().Count();
             this.GameInstance.Window.Title = $"Stardew Valley {Constants.GameVersion} - running SMAPI {Constants.ApiVersion} with {modsLoaded} mods";
             Console.Title = $"SMAPI {Constants.ApiVersion} - running Stardew Valley {Constants.GameVersion} with {modsLoaded} mods";
 
@@ -390,7 +390,7 @@ namespace StardewModdingAPI
             LocalizedContentManager.LanguageCode languageCode = this.ContentManager.GetCurrentLanguage();
 
             // update mod translation helpers
-            foreach (IModMetadata mod in this.ModRegistry.GetMods())
+            foreach (IModMetadata mod in this.ModRegistry.GetAll())
                 (mod.Mod.Helper.Translation as TranslationHelper)?.SetLocale(locale, languageCode);
         }
 
@@ -655,6 +655,7 @@ namespace StardewModdingAPI
 
                 AssemblyLoader modAssemblyLoader = new AssemblyLoader(Constants.TargetPlatform, this.Monitor, this.Settings.DeveloperMode);
                 AppDomain.CurrentDomain.AssemblyResolve += (sender, e) => modAssemblyLoader.ResolveAssembly(e.Name);
+                InterfaceProxyBuilder proxyBuilder = new InterfaceProxyBuilder();
                 foreach (IModMetadata metadata in mods)
                 {
                     // get basic info
@@ -696,53 +697,30 @@ namespace StardewModdingAPI
                         continue;
                     }
 
-                    // validate assembly
-                    try
-                    {
-                        int modEntries = modAssembly.DefinedTypes.Count(type => typeof(Mod).IsAssignableFrom(type) && !type.IsAbstract);
-                        if (modEntries == 0)
-                        {
-                            TrackSkip(metadata, $"its DLL has no '{nameof(Mod)}' subclass.");
-                            continue;
-                        }
-                        if (modEntries > 1)
-                        {
-                            TrackSkip(metadata, $"its DLL contains multiple '{nameof(Mod)}' subclasses.");
-                            continue;
-                        }
-                    }
-                    catch (Exception ex)
-                    {
-                        TrackSkip(metadata, $"its DLL couldn't be loaded:\n{ex.GetLogSummary()}");
-                        continue;
-                    }
-
                     // initialise mod
                     try
                     {
-                        // get implementation
-                        TypeInfo modEntryType = modAssembly.DefinedTypes.First(type => typeof(Mod).IsAssignableFrom(type) && !type.IsAbstract);
-                        Mod mod = (Mod)modAssembly.CreateInstance(modEntryType.ToString());
-                        if (mod == null)
-                        {
-                            TrackSkip(metadata, "its entry class couldn't be instantiated.");
-                            continue;
-                        }
-
-                        // inject data
+                        // init mod helpers
+                        IMonitor monitor = this.GetSecondaryMonitor(metadata.DisplayName);
+                        IModHelper modHelper;
                         {
-                            IMonitor monitor = this.GetSecondaryMonitor(metadata.DisplayName);
                             ICommandHelper commandHelper = new CommandHelper(manifest.UniqueID, metadata.DisplayName, this.CommandManager);
                             IContentHelper contentHelper = new ContentHelper(contentManager, metadata.DirectoryPath, manifest.UniqueID, metadata.DisplayName, monitor);
                             IReflectionHelper reflectionHelper = new ReflectionHelper(manifest.UniqueID, metadata.DisplayName, this.Reflection, this.DeprecationManager);
-                            IModRegistry modRegistryHelper = new ModRegistryHelper(manifest.UniqueID, this.ModRegistry);
+                            IModRegistry modRegistryHelper = new ModRegistryHelper(manifest.UniqueID, this.ModRegistry, proxyBuilder, monitor);
                             ITranslationHelper translationHelper = new TranslationHelper(manifest.UniqueID, manifest.Name, contentManager.GetLocale(), contentManager.GetCurrentLanguage());
-
-                            mod.ModManifest = manifest;
-                            mod.Helper = new ModHelper(manifest.UniqueID, metadata.DirectoryPath, jsonHelper, contentHelper, commandHelper, modRegistryHelper, reflectionHelper, translationHelper);
-                            mod.Monitor = monitor;
+                            modHelper = new ModHelper(manifest.UniqueID, metadata.DirectoryPath, jsonHelper, contentHelper, commandHelper, modRegistryHelper, reflectionHelper, translationHelper);
                         }
 
+                        // get mod instance
+                        if (!this.TryLoadModEntry(modAssembly, error => TrackSkip(metadata, error), out Mod mod))
+                            continue;
+
+                        // init mod
+                        mod.ModManifest = manifest;
+                        mod.Helper = modHelper;
+                        mod.Monitor = monitor;
+
                         // track mod
                         metadata.SetMod(mod);
                         this.ModRegistry.Add(metadata);
@@ -753,7 +731,7 @@ namespace StardewModdingAPI
                     }
                 }
             }
-            IModMetadata[] loadedMods = this.ModRegistry.GetMods().ToArray();
+            IModMetadata[] loadedMods = this.ModRegistry.GetAll().ToArray();
 
             // log skipped mods
             this.Monitor.Newline();
@@ -817,6 +795,19 @@ namespace StardewModdingAPI
                 {
                     this.Monitor.Log($"{metadata.DisplayName} failed on entry and might not work correctly. Technical details:\n{ex.GetLogSummary()}", LogLevel.Error);
                 }
+
+                // get mod API
+                try
+                {
+                    object api = metadata.Mod.GetApi();
+                    if (api != null)
+                        this.Monitor.Log($"   Found mod-provided API ({api.GetType().FullName}).", LogLevel.Trace);
+                    metadata.SetApi(api);
+                }
+                catch (Exception ex)
+                {
+                    this.Monitor.Log($"Failed loading mod-provided API for {metadata.DisplayName}. Integrations with other mods may not work. Error: {ex.GetLogSummary()}", LogLevel.Error);
+                }
             }
 
             // invalidate cache entries when needed
@@ -852,13 +843,48 @@ namespace StardewModdingAPI
                 this.Monitor.Log("Invalidating cached assets for new editors & loaders...", LogLevel.Trace);
                 this.ContentManager.InvalidateCacheFor(editors, loaders);
             }
+
+            // unlock mod integrations
+            this.ModRegistry.AreAllModsInitialised = true;
+        }
+
+        /// <summary>Load a mod's entry class.</summary>
+        /// <param name="modAssembly">The mod assembly.</param>
+        /// <param name="onError">A callback invoked when loading fails.</param>
+        /// <param name="mod">The loaded instance.</param>
+        private bool TryLoadModEntry(Assembly modAssembly, Action<string> onError, out Mod mod)
+        {
+            mod = null;
+
+            // find type
+            TypeInfo[] modEntries = modAssembly.DefinedTypes.Where(type => typeof(Mod).IsAssignableFrom(type) && !type.IsAbstract).Take(2).ToArray();
+            if (modEntries.Length == 0)
+            {
+                onError($"its DLL has no '{nameof(Mod)}' subclass.");
+                return false;
+            }
+            if (modEntries.Length > 1)
+            {
+                onError($"its DLL contains multiple '{nameof(Mod)}' subclasses.");
+                return false;
+            }
+
+            // get implementation
+            mod = (Mod)modAssembly.CreateInstance(modEntries[0].ToString());
+            if (mod == null)
+            {
+                onError("its entry class couldn't be instantiated.");
+                return false;
+            }
+
+            return true;
         }
 
         /// <summary>Reload translations for all mods.</summary>
         private void ReloadTranslations()
         {
             JsonHelper jsonHelper = new JsonHelper();
-            foreach (IModMetadata metadata in this.ModRegistry.GetMods())
+            foreach (IModMetadata metadata in this.ModRegistry.GetAll())
             {
                 // read translation files
                 IDictionary<string, IDictionary<string, string>> translations = new Dictionary<string, IDictionary<string, string>>();
diff --git a/src/SMAPI/StardewModdingAPI.csproj b/src/SMAPI/StardewModdingAPI.csproj
index 0db94843..f76ac439 100644
--- a/src/SMAPI/StardewModdingAPI.csproj
+++ b/src/SMAPI/StardewModdingAPI.csproj
@@ -79,10 +79,6 @@
       <Private>True</Private>
     </Reference>
     <Reference Include="System.Windows.Forms" Condition="$(OS) == 'Windows_NT'" />
-    <Reference Include="System.Xml.Linq" />
-    <Reference Include="System.Data.DataSetExtensions" />
-    <Reference Include="Microsoft.CSharp" />
-    <Reference Include="System.Data" />
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
@@ -110,6 +106,7 @@
     <Compile Include="Framework\ContentManagerShim.cs" />
     <Compile Include="Framework\Exceptions\SAssemblyLoadFailedException.cs" />
     <Compile Include="Framework\ModLoading\AssemblyLoadStatus.cs" />
+    <Compile Include="Framework\Reflection\InterfaceProxyBuilder.cs" />
     <Compile Include="Framework\Utilities\ContextHash.cs" />
     <Compile Include="IReflectedField.cs" />
     <Compile Include="IReflectedMethod.cs" />