1 files changed, 128 insertions, 0 deletions
diff --git a/src/StardewModdingAPI/Framework/ModAssemblyLoader.cs b/src/StardewModdingAPI/Framework/ModAssemblyLoader.cs
new file mode 100644
index 00000000..e095cde8
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/ModAssemblyLoader.cs
@@ -0,0 +1,128 @@
+using System;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using System.Security.Cryptography;
+using Mono.Cecil;
+using StardewModdingAPI.AssemblyRewriters;
+using StardewModdingAPI.Framework.AssemblyRewriting;
+
+namespace StardewModdingAPI.Framework
+{
+    /// <summary>Preprocesses and loads mod assemblies.</summary>
+    internal class ModAssemblyLoader
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>The directory in which to cache data.</summary>
+        private readonly string CacheDirPath;
+
+        /// <summary>Metadata for mapping assemblies to the current <see cref="Platform"/>.</summary>
+        private readonly PlatformAssemblyMap AssemblyMap;
+
+        /// <summary>Rewrites assembly types to match the current platform.</summary>
+        private readonly AssemblyTypeRewriter AssemblyTypeRewriter;
+
+        /// <summary>Encapsulates monitoring and logging.</summary>
+        private readonly IMonitor Monitor;
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="cacheDirPath">The cache directory.</param>
+        /// <param name="targetPlatform">The current game platform.</param>
+        /// <param name="monitor">Encapsulates monitoring and logging.</param>
+        public ModAssemblyLoader(string cacheDirPath, Platform targetPlatform, IMonitor monitor)
+        {
+            this.CacheDirPath = cacheDirPath;
+            this.Monitor = monitor;
+            this.AssemblyMap = Constants.GetAssemblyMap(targetPlatform);
+            this.AssemblyTypeRewriter = new AssemblyTypeRewriter(this.AssemblyMap, monitor);
+        }
+
+        /// <summary>Preprocess an assembly and cache the modified version.</summary>
+        /// <param name="assemblyPath">The assembly file path.</param>
+        public void ProcessAssembly(string assemblyPath)
+        {
+            // read assembly data
+            string assemblyFileName = Path.GetFileName(assemblyPath);
+            string assemblyDir = Path.GetDirectoryName(assemblyPath);
+            byte[] assemblyBytes = File.ReadAllBytes(assemblyPath);
+            byte[] hash = MD5.Create().ComputeHash(assemblyBytes);
+
+            // check cache
+            CachePaths cachePaths = this.GetCacheInfo(assemblyPath);
+            bool canUseCache = File.Exists(cachePaths.Assembly) && File.Exists(cachePaths.Hash) && hash.SequenceEqual(File.ReadAllBytes(cachePaths.Hash));
+
+            // process assembly if not cached
+            if (!canUseCache)
+            {
+                this.Monitor.Log($"Loading {assemblyFileName} for the first time; preprocessing...");
+
+                // read assembly definition
+                AssemblyDefinition assembly;
+                using (Stream readStream = new MemoryStream(assemblyBytes))
+                    assembly = AssemblyDefinition.ReadAssembly(readStream);
+
+                // rewrite assembly to match platform
+                this.AssemblyTypeRewriter.RewriteAssembly(assembly);
+
+                // write cache
+                using (MemoryStream outStream = new MemoryStream())
+                {
+                    // get assembly bytes
+                    assembly.Write(outStream);
+                    byte[] outBytes = outStream.ToArray();
+
+                    // write assembly data
+                    Directory.CreateDirectory(cachePaths.Directory);
+                    File.WriteAllBytes(cachePaths.Assembly, outBytes);
+                    File.WriteAllBytes(cachePaths.Hash, hash);
+
+                    // copy any mdb/pdb files
+                    foreach (string path in Directory.GetFiles(assemblyDir, "*.mdb").Concat(Directory.GetFiles(assemblyDir, "*.pdb")))
+                    {
+                        string filename = Path.GetFileName(path);
+                        File.Copy(path, Path.Combine(cachePaths.Directory, filename), overwrite: true);
+                    }
+                }
+            }
+        }
+
+        /// <summary>Load a preprocessed assembly.</summary>
+        /// <param name="assemblyPath">The assembly file path.</param>
+        public Assembly LoadCachedAssembly(string assemblyPath)
+        {
+            CachePaths cachePaths = this.GetCacheInfo(assemblyPath);
+            if (!File.Exists(cachePaths.Assembly))
+                throw new InvalidOperationException($"The assembly {assemblyPath} doesn't exist in the preprocessed cache.");
+            return Assembly.UnsafeLoadFrom(cachePaths.Assembly); // unsafe load allows DLLs downloaded from the Internet without the user needing to 'unblock' them
+        }
+
+        /// <summary>Resolve an assembly from its name.</summary>
+        /// <param name="name">The assembly name.</param>
+        public Assembly ResolveAssembly(string name)
+        {
+            string shortName = name.Split(new[] { ',' }, 2).First();
+            return this.AssemblyMap.Targets.FirstOrDefault(p => p.GetName().Name == shortName);
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Get the cache details for an assembly.</summary>
+        /// <param name="assemblyPath">The assembly file path.</param>
+        private CachePaths GetCacheInfo(string assemblyPath)
+        {
+            string key = Path.GetFileNameWithoutExtension(assemblyPath);
+            string dirPath = Path.Combine(this.CacheDirPath, new DirectoryInfo(Path.GetDirectoryName(assemblyPath)).Name);
+            string cacheAssemblyPath = Path.Combine(dirPath, $"{key}.dll");
+            string cacheHashPath = Path.Combine(dirPath, $"{key}.hash");
+            return new CachePaths(dirPath, cacheAssemblyPath, cacheHashPath);
+        }
+    }
+}