1 files changed, 58 insertions, 0 deletions
diff --git a/src/SMAPI/Framework/Reflection/InterfaceProxyFactory.cs b/src/SMAPI/Framework/Reflection/InterfaceProxyFactory.cs
new file mode 100644
index 00000000..e14a9f08
--- /dev/null
+++ b/src/SMAPI/Framework/Reflection/InterfaceProxyFactory.cs
@@ -0,0 +1,58 @@
+using System;
+using System.Collections.Generic;
+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 InterfaceProxyFactory
+    {
+        /*********
+        ** 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, InterfaceProxyBuilder> Builders = new Dictionary<string, InterfaceProxyBuilder>();
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        public InterfaceProxyFactory()
+        {
+            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.Builders.TryGetValue(proxyTypeName, out InterfaceProxyBuilder builder))
+            {
+                builder = new InterfaceProxyBuilder(proxyTypeName, this.ModuleBuilder, typeof(TInterface), targetType);
+                this.Builders[proxyTypeName] = builder;
+            }
+
+            // create instance
+            return (TInterface)builder.CreateInstance(instance);
+        }
+    }
+}