Merge branch 'develop' into stable

9 files changed, 815 insertions, 0 deletions

diff --git a/src/StardewModdingAPI/Framework/ModLoading/AssemblyDefinitionResolver.cs b/src/StardewModdingAPI/Framework/ModLoading/AssemblyDefinitionResolver.cs
new file mode 100644
index 00000000..4378798c
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/ModLoading/AssemblyDefinitionResolver.cs
@@ -0,0 +1,61 @@
+using System.Collections.Generic;
+using Mono.Cecil;
+
+namespace StardewModdingAPI.Framework.ModLoading
+{
+    /// <summary>A minimal assembly definition resolver which resolves references to known assemblies.</summary>
+    internal class AssemblyDefinitionResolver : DefaultAssemblyResolver
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>The known assemblies.</summary>
+        private readonly IDictionary<string, AssemblyDefinition> Loaded = new Dictionary<string, AssemblyDefinition>();
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Add known assemblies to the resolver.</summary>
+        /// <param name="assemblies">The known assemblies.</param>
+        public void Add(params AssemblyDefinition[] assemblies)
+        {
+            foreach (AssemblyDefinition assembly in assemblies)
+            {
+                this.Loaded[assembly.Name.Name] = assembly;
+                this.Loaded[assembly.Name.FullName] = assembly;
+            }
+        }
+
+        /// <summary>Resolve an assembly reference.</summary>
+        /// <param name="name">The assembly name.</param>
+        public override AssemblyDefinition Resolve(AssemblyNameReference name) => this.ResolveName(name.Name) ?? base.Resolve(name);
+
+        /// <summary>Resolve an assembly reference.</summary>
+        /// <param name="name">The assembly name.</param>
+        /// <param name="parameters">The assembly reader parameters.</param>
+        public override AssemblyDefinition Resolve(AssemblyNameReference name, ReaderParameters parameters) => this.ResolveName(name.Name) ?? base.Resolve(name, parameters);
+
+        /// <summary>Resolve an assembly reference.</summary>
+        /// <param name="fullName">The assembly full name (including version, etc).</param>
+        public override AssemblyDefinition Resolve(string fullName) => this.ResolveName(fullName) ?? base.Resolve(fullName);
+
+        /// <summary>Resolve an assembly reference.</summary>
+        /// <param name="fullName">The assembly full name (including version, etc).</param>
+        /// <param name="parameters">The assembly reader parameters.</param>
+        public override AssemblyDefinition Resolve(string fullName, ReaderParameters parameters) => this.ResolveName(fullName) ?? base.Resolve(fullName, parameters);
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Resolve a known assembly definition based on its short or full name.</summary>
+        /// <param name="name">The assembly's short or full name.</param>
+        private AssemblyDefinition ResolveName(string name)
+        {
+            return this.Loaded.ContainsKey(name)
+                ? this.Loaded[name]
+                : null;
+        }
+    }
+}
diff --git a/src/StardewModdingAPI/Framework/ModLoading/AssemblyLoader.cs b/src/StardewModdingAPI/Framework/ModLoading/AssemblyLoader.cs
new file mode 100644
index 00000000..42bd7bfb
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/ModLoading/AssemblyLoader.cs
@@ -0,0 +1,292 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using Mono.Cecil;
+using Mono.Cecil.Cil;
+using StardewModdingAPI.AssemblyRewriters;
+
+namespace StardewModdingAPI.Framework.ModLoading
+{
+    /// <summary>Preprocesses and loads mod assemblies.</summary>
+    internal class AssemblyLoader
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>Metadata for mapping assemblies to the current platform.</summary>
+        private readonly PlatformAssemblyMap AssemblyMap;
+
+        /// <summary>A type => assembly lookup for types which should be rewritten.</summary>
+        private readonly IDictionary<string, Assembly> TypeAssemblies;
+
+        /// <summary>Encapsulates monitoring and logging.</summary>
+        private readonly IMonitor Monitor;
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="targetPlatform">The current game platform.</param>
+        /// <param name="monitor">Encapsulates monitoring and logging.</param>
+        public AssemblyLoader(Platform targetPlatform, IMonitor monitor)
+        {
+            this.Monitor = monitor;
+            this.AssemblyMap = Constants.GetAssemblyMap(targetPlatform);
+
+            // generate type => assembly lookup for types which should be rewritten
+            this.TypeAssemblies = new Dictionary<string, Assembly>();
+            foreach (Assembly assembly in this.AssemblyMap.Targets)
+            {
+                ModuleDefinition module = this.AssemblyMap.TargetModules[assembly];
+                foreach (TypeDefinition type in module.GetTypes())
+                {
+                    if (!type.IsPublic)
+                        continue; // no need to rewrite
+                    if (type.Namespace.Contains("<"))
+                        continue; // ignore assembly metadata
+                    this.TypeAssemblies[type.FullName] = assembly;
+                }
+            }
+        }
+
+        /// <summary>Preprocess and load an assembly.</summary>
+        /// <param name="assemblyPath">The assembly file path.</param>
+        /// <param name="assumeCompatible">Assume the mod is compatible, even if incompatible code is detected.</param>
+        /// <returns>Returns the rewrite metadata for the preprocessed assembly.</returns>
+        /// <exception cref="IncompatibleInstructionException">An incompatible CIL instruction was found while rewriting the assembly.</exception>
+        public Assembly Load(string assemblyPath, bool assumeCompatible)
+        {
+            // get referenced local assemblies
+            AssemblyParseResult[] assemblies;
+            {
+                AssemblyDefinitionResolver resolver = new AssemblyDefinitionResolver();
+                HashSet<string> visitedAssemblyNames = new HashSet<string>(AppDomain.CurrentDomain.GetAssemblies().Select(p => p.GetName().Name)); // don't try loading assemblies that are already loaded
+                assemblies = this.GetReferencedLocalAssemblies(new FileInfo(assemblyPath), visitedAssemblyNames, resolver).ToArray();
+                if (!assemblies.Any())
+                    throw new InvalidOperationException($"Could not load '{assemblyPath}' because it doesn't exist.");
+                resolver.Add(assemblies.Select(p => p.Definition).ToArray());
+            }
+
+            // rewrite & load assemblies in leaf-to-root order
+            Assembly lastAssembly = null;
+            foreach (AssemblyParseResult assembly in assemblies)
+            {
+                bool changed = this.RewriteAssembly(assembly.Definition, assumeCompatible);
+                if (changed)
+                {
+                    this.Monitor.Log($"Loading {assembly.File.Name} (rewritten in memory)...", LogLevel.Trace);
+                    using (MemoryStream outStream = new MemoryStream())
+                    {
+                        assembly.Definition.Write(outStream);
+                        byte[] bytes = outStream.ToArray();
+                        lastAssembly = Assembly.Load(bytes);
+                    }
+                }
+                else
+                {
+                    this.Monitor.Log($"Loading {assembly.File.Name}...", LogLevel.Trace);
+                    lastAssembly = Assembly.UnsafeLoadFrom(assembly.File.FullName);
+                }
+            }
+
+            // last assembly loaded is the root
+            return lastAssembly;
+        }
+
+        /// <summary>Resolve an assembly by its name.</summary>
+        /// <param name="name">The assembly name.</param>
+        /// <remarks>
+        /// This implementation returns the first loaded assembly which matches the short form of
+        /// the assembly name, to resolve assembly resolution issues when rewriting
+        /// assemblies (especially with Mono). Since this is meant to be called on <see cref="AppDomain.AssemblyResolve"/>,
+        /// the implicit assumption is that loading the exact assembly failed.
+        /// </remarks>
+        public Assembly ResolveAssembly(string name)
+        {
+            string shortName = name.Split(new[] { ',' }, 2).First(); // get simple name (without version and culture)
+            return AppDomain.CurrentDomain
+                .GetAssemblies()
+                .FirstOrDefault(p => p.GetName().Name == shortName);
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /****
+        ** Assembly parsing
+        ****/
+        /// <summary>Get a list of referenced local assemblies starting from the mod assembly, ordered from leaf to root.</summary>
+        /// <param name="file">The assembly file to load.</param>
+        /// <param name="visitedAssemblyNames">The assembly names that should be skipped.</param>
+        /// <param name="assemblyResolver">A resolver which resolves references to known assemblies.</param>
+        /// <returns>Returns the rewrite metadata for the preprocessed assembly.</returns>
+        private IEnumerable<AssemblyParseResult> GetReferencedLocalAssemblies(FileInfo file, HashSet<string> visitedAssemblyNames, IAssemblyResolver assemblyResolver)
+        {
+            // validate
+            if (file.Directory == null)
+                throw new InvalidOperationException($"Could not get directory from file path '{file.FullName}'.");
+            if (!file.Exists)
+                yield break; // not a local assembly
+
+            // read assembly
+            byte[] assemblyBytes = File.ReadAllBytes(file.FullName);
+            AssemblyDefinition assembly;
+            using (Stream readStream = new MemoryStream(assemblyBytes))
+                assembly = AssemblyDefinition.ReadAssembly(readStream, new ReaderParameters(ReadingMode.Deferred) { AssemblyResolver = assemblyResolver });
+
+            // skip if already visited
+            if (visitedAssemblyNames.Contains(assembly.Name.Name))
+                yield break;
+            visitedAssemblyNames.Add(assembly.Name.Name);
+
+            // yield referenced assemblies
+            foreach (AssemblyNameReference dependency in assembly.MainModule.AssemblyReferences)
+            {
+                FileInfo dependencyFile = new FileInfo(Path.Combine(file.Directory.FullName, $"{dependency.Name}.dll"));
+                foreach (AssemblyParseResult result in this.GetReferencedLocalAssemblies(dependencyFile, visitedAssemblyNames, assemblyResolver))
+                    yield return result;
+            }
+
+            // yield assembly
+            yield return new AssemblyParseResult(file, assembly);
+        }
+
+        /****
+        ** Assembly rewriting
+        ****/
+        /// <summary>Rewrite the types referenced by an assembly.</summary>
+        /// <param name="assembly">The assembly to rewrite.</param>
+        /// <param name="assumeCompatible">Assume the mod is compatible, even if incompatible code is detected.</param>
+        /// <returns>Returns whether the assembly was modified.</returns>
+        /// <exception cref="IncompatibleInstructionException">An incompatible CIL instruction was found while rewriting the assembly.</exception>
+        private bool RewriteAssembly(AssemblyDefinition assembly, bool assumeCompatible)
+        {
+            ModuleDefinition module = assembly.MainModule;
+            HashSet<string> loggedMessages = new HashSet<string>();
+
+            // swap assembly references if needed (e.g. XNA => MonoGame)
+            bool platformChanged = false;
+            for (int i = 0; i < module.AssemblyReferences.Count; i++)
+            {
+                // remove old assembly reference
+                if (this.AssemblyMap.RemoveNames.Any(name => module.AssemblyReferences[i].Name == name))
+                {
+                    this.LogOnce(this.Monitor, loggedMessages, $"Rewriting {assembly.Name.Name} for OS...");
+                    platformChanged = true;
+                    module.AssemblyReferences.RemoveAt(i);
+                    i--;
+                }
+            }
+            if (platformChanged)
+            {
+                // add target assembly references
+                foreach (AssemblyNameReference target in this.AssemblyMap.TargetReferences.Values)
+                    module.AssemblyReferences.Add(target);
+
+                // rewrite type scopes to use target assemblies
+                IEnumerable<TypeReference> typeReferences = module.GetTypeReferences().OrderBy(p => p.FullName);
+                foreach (TypeReference type in typeReferences)
+                    this.ChangeTypeScope(type);
+            }
+
+            // find (and optionally rewrite) incompatible instructions
+            bool anyRewritten = false;
+            IInstructionRewriter[] rewriters = Constants.GetRewriters().ToArray();
+            foreach (MethodDefinition method in this.GetMethods(module))
+            {
+                // check method definition
+                foreach (IInstructionRewriter rewriter in rewriters)
+                {
+                    try
+                    {
+                        if (rewriter.Rewrite(module, method, this.AssemblyMap, platformChanged))
+                        {
+                            this.LogOnce(this.Monitor, loggedMessages, $"Rewrote {assembly.Name.Name} to fix {rewriter.NounPhrase}...");
+                            anyRewritten = true;
+                        }
+                    }
+                    catch (IncompatibleInstructionException)
+                    {
+                        if (!assumeCompatible)
+                            throw new IncompatibleInstructionException(rewriter.NounPhrase, $"Found an incompatible CIL instruction ({rewriter.NounPhrase}) while loading assembly {assembly.Name.Name}.");
+                        this.LogOnce(this.Monitor, loggedMessages, $"Found an incompatible CIL instruction ({rewriter.NounPhrase}) while loading assembly {assembly.Name.Name}, but SMAPI is configured to allow it anyway. The mod may crash or behave unexpectedly.", LogLevel.Warn);
+                    }
+                }
+
+                // check CIL instructions
+                ILProcessor cil = method.Body.GetILProcessor();
+                foreach (Instruction instruction in cil.Body.Instructions.ToArray())
+                {
+                    foreach (IInstructionRewriter rewriter in rewriters)
+                    {
+                        try
+                        {
+                            if (rewriter.Rewrite(module, cil, instruction, this.AssemblyMap, platformChanged))
+                            {
+                                this.LogOnce(this.Monitor, loggedMessages, $"Rewrote {assembly.Name.Name} to fix {rewriter.NounPhrase}...");
+                                anyRewritten = true;
+                            }
+                        }
+                        catch (IncompatibleInstructionException)
+                        {
+                            if (!assumeCompatible)
+                                throw new IncompatibleInstructionException(rewriter.NounPhrase, $"Found an incompatible CIL instruction ({rewriter.NounPhrase}) while loading assembly {assembly.Name.Name}.");
+                            this.LogOnce(this.Monitor, loggedMessages, $"Found an incompatible CIL instruction ({rewriter.NounPhrase}) while loading assembly {assembly.Name.Name}, but SMAPI is configured to allow it anyway. The mod may crash or behave unexpectedly.", LogLevel.Warn);
+                        }
+                    }
+                }
+            }
+
+            return platformChanged || anyRewritten;
+        }
+
+        /// <summary>Get the correct reference to use for compatibility with the current platform.</summary>
+        /// <param name="type">The type reference to rewrite.</param>
+        private void ChangeTypeScope(TypeReference type)
+        {
+            // check skip conditions
+            if (type == null || type.FullName.StartsWith("System."))
+                return;
+
+            // get assembly
+            Assembly assembly;
+            if (!this.TypeAssemblies.TryGetValue(type.FullName, out assembly))
+                return;
+
+            // replace scope
+            AssemblyNameReference assemblyRef = this.AssemblyMap.TargetReferences[assembly];
+            type.Scope = assemblyRef;
+        }
+
+        /// <summary>Get all methods in a module.</summary>
+        /// <param name="module">The module to search.</param>
+        private IEnumerable<MethodDefinition> GetMethods(ModuleDefinition module)
+        {
+            return (
+                from type in module.GetTypes()
+                where type.HasMethods
+                from method in type.Methods
+                where method.HasBody
+                select method
+            );
+        }
+
+        /// <summary>Log a message for the player or developer the first time it occurs.</summary>
+        /// <param name="monitor">The monitor through which to log the message.</param>
+        /// <param name="hash">The hash of logged messages.</param>
+        /// <param name="message">The message to log.</param>
+        /// <param name="level">The log severity level.</param>
+        private void LogOnce(IMonitor monitor, HashSet<string> hash, string message, LogLevel level = LogLevel.Trace)
+        {
+            if (!hash.Contains(message))
+            {
+                monitor.Log(message, level);
+                hash.Add(message);
+            }
+        }
+    }
+}
diff --git a/src/StardewModdingAPI/Framework/ModLoading/AssemblyParseResult.cs b/src/StardewModdingAPI/Framework/ModLoading/AssemblyParseResult.cs
new file mode 100644
index 00000000..69c99afe
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/ModLoading/AssemblyParseResult.cs
@@ -0,0 +1,31 @@
+using System.IO;
+using Mono.Cecil;
+
+namespace StardewModdingAPI.Framework.ModLoading
+{
+    /// <summary>Metadata about a parsed assembly definition.</summary>
+    internal class AssemblyParseResult
+    {
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>The original assembly file.</summary>
+        public readonly FileInfo File;
+
+        /// <summary>The assembly definition.</summary>
+        public readonly AssemblyDefinition Definition;
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="file">The original assembly file.</param>
+        /// <param name="assembly">The assembly definition.</param>
+        public AssemblyParseResult(FileInfo file, AssemblyDefinition assembly)
+        {
+            this.File = file;
+            this.Definition = assembly;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/StardewModdingAPI/Framework/ModLoading/IModMetadata.cs b/src/StardewModdingAPI/Framework/ModLoading/IModMetadata.cs
new file mode 100644
index 00000000..3771ffdd
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/ModLoading/IModMetadata.cs
@@ -0,0 +1,39 @@
+using StardewModdingAPI.Framework.Models;
+
+namespace StardewModdingAPI.Framework.ModLoading
+{
+    /// <summary>Metadata for a mod.</summary>
+    internal interface IModMetadata
+    {
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>The mod's display name.</summary>
+        string DisplayName { get; }
+
+        /// <summary>The mod's full directory path.</summary>
+        string DirectoryPath { get; }
+
+        /// <summary>The mod manifest.</summary>
+        IManifest Manifest { get; }
+
+        /// <summary>Optional metadata about a mod version that SMAPI should assume is compatible or broken, regardless of whether it detects incompatible code.</summary>
+        ModCompatibility Compatibility { get; }
+
+        /// <summary>The metadata resolution status.</summary>
+        ModMetadataStatus Status { get; }
+
+        /// <summary>The reason the metadata is invalid, if any.</summary>
+        string Error { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Set the mod status.</summary>
+        /// <param name="status">The metadata resolution status.</param>
+        /// <param name="error">The reason the metadata is invalid, if any.</param>
+        /// <returns>Return the instance for chaining.</returns>
+        IModMetadata SetStatus(ModMetadataStatus status, string error = null);
+    }
+}
diff --git a/src/StardewModdingAPI/Framework/ModLoading/InvalidModStateException.cs b/src/StardewModdingAPI/Framework/ModLoading/InvalidModStateException.cs
new file mode 100644
index 00000000..ab11272a
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/ModLoading/InvalidModStateException.cs
@@ -0,0 +1,14 @@
+using System;
+
+namespace StardewModdingAPI.Framework.ModLoading
+{
+    /// <summary>An exception which indicates that something went seriously wrong while loading mods, and SMAPI should abort outright.</summary>
+    public class InvalidModStateException : Exception
+    {
+        /// <summary>Construct an instance.</summary>
+        /// <param name="message">The error message.</param>
+        /// <param name="ex">The underlying exception, if any.</param>
+        public InvalidModStateException(string message, Exception ex = null)
+            : base(message, ex) { }
+    }
+}
diff --git a/src/StardewModdingAPI/Framework/ModLoading/ModDependencyStatus.cs b/src/StardewModdingAPI/Framework/ModLoading/ModDependencyStatus.cs
new file mode 100644
index 00000000..0774b487
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/ModLoading/ModDependencyStatus.cs
@@ -0,0 +1,18 @@
+namespace StardewModdingAPI.Framework.ModLoading
+{
+    /// <summary>The status of a given mod in the dependency-sorting algorithm.</summary>
+    internal enum ModDependencyStatus
+    {
+        /// <summary>The mod hasn't been visited yet.</summary>
+        Queued,
+
+        /// <summary>The mod is currently being analysed as part of a dependency chain.</summary>
+        Checking,
+
+        /// <summary>The mod has already been sorted.</summary>
+        Sorted,
+
+        /// <summary>The mod couldn't be sorted due to a metadata issue (e.g. missing dependencies).</summary>
+        Failed
+    }
+}
diff --git a/src/StardewModdingAPI/Framework/ModLoading/ModMetadata.cs b/src/StardewModdingAPI/Framework/ModLoading/ModMetadata.cs
new file mode 100644
index 00000000..7b25e090
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/ModLoading/ModMetadata.cs
@@ -0,0 +1,57 @@
+using StardewModdingAPI.Framework.Models;
+
+namespace StardewModdingAPI.Framework.ModLoading
+{
+    /// <summary>Metadata for a mod.</summary>
+    internal class ModMetadata : IModMetadata
+    {
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>The mod's display name.</summary>
+        public string DisplayName { get; }
+
+        /// <summary>The mod's full directory path.</summary>
+        public string DirectoryPath { get; }
+
+        /// <summary>The mod manifest.</summary>
+        public IManifest Manifest { get; }
+
+        /// <summary>Optional metadata about a mod version that SMAPI should assume is compatible or broken, regardless of whether it detects incompatible code.</summary>
+        public ModCompatibility Compatibility { get; }
+
+        /// <summary>The metadata resolution status.</summary>
+        public ModMetadataStatus Status { get; private set; }
+
+        /// <summary>The reason the metadata is invalid, if any.</summary>
+        public string Error { get; private set; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="displayName">The mod's display name.</param>
+        /// <param name="directoryPath">The mod's full directory path.</param>
+        /// <param name="manifest">The mod manifest.</param>
+        /// <param name="compatibility">Optional metadata about a mod version that SMAPI should assume is compatible or broken, regardless of whether it detects incompatible code.</param>
+        public ModMetadata(string displayName, string directoryPath, IManifest manifest, ModCompatibility compatibility)
+        {
+            this.DisplayName = displayName;
+            this.DirectoryPath = directoryPath;
+            this.Manifest = manifest;
+            this.Compatibility = compatibility;
+        }
+
+        /// <summary>Set the mod status.</summary>
+        /// <param name="status">The metadata resolution status.</param>
+        /// <param name="error">The reason the metadata is invalid, if any.</param>
+        /// <returns>Return the instance for chaining.</returns>
+        public IModMetadata SetStatus(ModMetadataStatus status, string error = null)
+        {
+            this.Status = status;
+            this.Error = error;
+            return this;
+        }
+    }
+}
diff --git a/src/StardewModdingAPI/Framework/ModLoading/ModMetadataStatus.cs b/src/StardewModdingAPI/Framework/ModLoading/ModMetadataStatus.cs
new file mode 100644
index 00000000..1b2b0b55
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/ModLoading/ModMetadataStatus.cs
@@ -0,0 +1,12 @@
+namespace StardewModdingAPI.Framework.ModLoading
+{
+    /// <summary>Indicates the status of a mod's metadata resolution.</summary>
+    internal enum ModMetadataStatus
+    {
+        /// <summary>The mod has been found, but hasn't been processed yet.</summary>
+        Found,
+
+        /// <summary>The mod cannot be loaded.</summary>
+        Failed
+    }
+}
\ No newline at end of file
diff --git a/src/StardewModdingAPI/Framework/ModLoading/ModResolver.cs b/src/StardewModdingAPI/Framework/ModLoading/ModResolver.cs
new file mode 100644
index 00000000..2c68a639
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/ModLoading/ModResolver.cs
@@ -0,0 +1,291 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using StardewModdingAPI.Framework.Models;
+using StardewModdingAPI.Framework.Serialisation;
+
+namespace StardewModdingAPI.Framework.ModLoading
+{
+    /// <summary>Finds and processes mod metadata.</summary>
+    internal class ModResolver
+    {
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Get manifest metadata for each folder in the given root path.</summary>
+        /// <param name="rootPath">The root path to search for mods.</param>
+        /// <param name="jsonHelper">The JSON helper with which to read manifests.</param>
+        /// <param name="compatibilityRecords">Metadata about mods that SMAPI should assume is compatible or broken, regardless of whether it detects incompatible code.</param>
+        /// <returns>Returns the manifests by relative folder.</returns>
+        public IEnumerable<IModMetadata> ReadManifests(string rootPath, JsonHelper jsonHelper, IEnumerable<ModCompatibility> compatibilityRecords)
+        {
+            compatibilityRecords = compatibilityRecords.ToArray();
+            foreach (DirectoryInfo modDir in this.GetModFolders(rootPath))
+            {
+                // read file
+                Manifest manifest = null;
+                string path = Path.Combine(modDir.FullName, "manifest.json");
+                string error = null;
+                try
+                {
+                    // read manifest
+                    manifest = jsonHelper.ReadJsonFile<Manifest>(path);
+
+                    // validate
+                    if (manifest == null)
+                    {
+                        error = File.Exists(path)
+                            ? "its manifest is invalid."
+                            : "it doesn't have a manifest.";
+                    }
+                    else if (string.IsNullOrWhiteSpace(manifest.EntryDll))
+                        error = "its manifest doesn't set an entry DLL.";
+                }
+                catch (Exception ex)
+                {
+                    error = $"parsing its manifest failed:\n{ex.GetLogSummary()}";
+                }
+
+                // get compatibility record
+                ModCompatibility compatibility = null;
+                if (manifest != null)
+                {
+                    string key = !string.IsNullOrWhiteSpace(manifest.UniqueID) ? manifest.UniqueID : manifest.EntryDll;
+                    compatibility = (
+                        from mod in compatibilityRecords
+                        where
+                            mod.ID.Contains(key, StringComparer.InvariantCultureIgnoreCase)
+                            && (mod.LowerSemanticVersion == null || !manifest.Version.IsOlderThan(mod.LowerSemanticVersion))
+                            && !manifest.Version.IsNewerThan(mod.UpperSemanticVersion)
+                        select mod
+                    ).FirstOrDefault();
+                }
+                // build metadata
+                string displayName = !string.IsNullOrWhiteSpace(manifest?.Name)
+                    ? manifest.Name
+                    : modDir.FullName.Replace(rootPath, "").Trim('/', '\\');
+                ModMetadataStatus status = error == null
+                    ? ModMetadataStatus.Found
+                    : ModMetadataStatus.Failed;
+
+                yield return new ModMetadata(displayName, modDir.FullName, manifest, compatibility).SetStatus(status, error);
+            }
+        }
+
+        /// <summary>Validate manifest metadata.</summary>
+        /// <param name="mods">The mod manifests to validate.</param>
+        /// <param name="apiVersion">The current SMAPI version.</param>
+        public void ValidateManifests(IEnumerable<IModMetadata> mods, ISemanticVersion apiVersion)
+        {
+            foreach (IModMetadata mod in mods)
+            {
+                // skip if already failed
+                if (mod.Status == ModMetadataStatus.Failed)
+                    continue;
+
+                // validate compatibility
+                {
+                    ModCompatibility compatibility = mod.Compatibility;
+                    if (compatibility?.Compatibility == ModCompatibilityType.AssumeBroken)
+                    {
+                        bool hasOfficialUrl = !string.IsNullOrWhiteSpace(mod.Compatibility.UpdateUrl);
+                        bool hasUnofficialUrl = !string.IsNullOrWhiteSpace(mod.Compatibility.UnofficialUpdateUrl);
+
+                        string reasonPhrase = compatibility.ReasonPhrase ?? "it's not compatible with the latest version of the game";
+                        string error = $"{reasonPhrase}. Please check for a version newer than {compatibility.UpperVersionLabel ?? compatibility.UpperVersion} here:";
+                        if (hasOfficialUrl)
+                            error += !hasUnofficialUrl ? $" {compatibility.UpdateUrl}" : $"{Environment.NewLine}- official mod: {compatibility.UpdateUrl}";
+                        if (hasUnofficialUrl)
+                            error += $"{Environment.NewLine}- unofficial update: {compatibility.UnofficialUpdateUrl}";
+
+                        mod.SetStatus(ModMetadataStatus.Failed, error);
+                        continue;
+                    }
+                }
+
+                // validate SMAPI version
+                if (!string.IsNullOrWhiteSpace(mod.Manifest.MinimumApiVersion))
+                {
+                    if (!SemanticVersion.TryParse(mod.Manifest.MinimumApiVersion, out ISemanticVersion minVersion))
+                    {
+                        mod.SetStatus(ModMetadataStatus.Failed, $"it has an invalid minimum SMAPI version '{mod.Manifest.MinimumApiVersion}'. This should be a semantic version number like {apiVersion}.");
+                        continue;
+                    }
+                    if (minVersion.IsNewerThan(apiVersion))
+                    {
+                        mod.SetStatus(ModMetadataStatus.Failed, $"it needs SMAPI {minVersion} or later. Please update SMAPI to the latest version to use this mod.");
+                        continue;
+                    }
+                }
+
+                // validate DLL path
+                string assemblyPath = Path.Combine(mod.DirectoryPath, mod.Manifest.EntryDll);
+                if (!File.Exists(assemblyPath))
+                    mod.SetStatus(ModMetadataStatus.Failed, $"its DLL '{mod.Manifest.EntryDll}' doesn't exist.");
+            }
+        }
+
+#if EXPERIMENTAL
+        /// <summary>Sort the given mods by the order they should be loaded.</summary>
+        /// <param name="mods">The mods to process.</param>
+        public IEnumerable<IModMetadata> ProcessDependencies(IEnumerable<IModMetadata> mods)
+        {
+            // initialise metadata
+            mods = mods.ToArray();
+            var sortedMods = new Stack<IModMetadata>();
+            var states = mods.ToDictionary(mod => mod, mod => ModDependencyStatus.Queued);
+
+            // handle failed mods
+            foreach (IModMetadata mod in mods.Where(m => m.Status == ModMetadataStatus.Failed))
+            {
+                states[mod] = ModDependencyStatus.Failed;
+                sortedMods.Push(mod);
+            }
+            
+            // sort mods
+            foreach (IModMetadata mod in mods)
+                this.ProcessDependencies(mods.ToArray(), mod, states, sortedMods, new List<IModMetadata>());
+
+            return sortedMods.Reverse();
+        }
+#endif
+
+
+        /*********
+        ** Private methods
+        *********/
+#if EXPERIMENTAL
+        /// <summary>Sort a mod's dependencies by the order they should be loaded, and remove any mods that can't be loaded due to missing or conflicting dependencies.</summary>
+        /// <param name="mods">The full list of mods being validated.</param>
+        /// <param name="mod">The mod whose dependencies to process.</param>
+        /// <param name="states">The dependency state for each mod.</param>
+        /// <param name="sortedMods">The list in which to save mods sorted by dependency order.</param>
+        /// <param name="currentChain">The current change of mod dependencies.</param>
+        /// <returns>Returns the mod dependency status.</returns>
+        private ModDependencyStatus ProcessDependencies(IModMetadata[] mods, IModMetadata mod, IDictionary<IModMetadata, ModDependencyStatus> states, Stack<IModMetadata> sortedMods, ICollection<IModMetadata> currentChain)
+        {
+            // check if already visited
+            switch (states[mod])
+            {
+                // already sorted or failed
+                case ModDependencyStatus.Sorted:
+                case ModDependencyStatus.Failed:
+                    return states[mod];
+
+                // dependency loop
+                case ModDependencyStatus.Checking:
+                    // This should never happen. The higher-level mod checks if the dependency is
+                    // already being checked, so it can fail without visiting a mod twice. If this
+                    // case is hit, that logic didn't catch the dependency loop for some reason.
+                    throw new InvalidModStateException($"A dependency loop was not caught by the calling iteration ({string.Join(" => ", currentChain.Select(p => p.DisplayName))} => {mod.DisplayName})).");
+
+                // not visited yet, start processing
+                case ModDependencyStatus.Queued:
+                    break;
+
+                // sanity check
+                default:
+                    throw new InvalidModStateException($"Unknown dependency status '{states[mod]}'.");
+            }
+
+            // no dependencies, mark sorted
+            if (mod.Manifest.Dependencies == null || !mod.Manifest.Dependencies.Any())
+            {
+                sortedMods.Push(mod);
+                return states[mod] = ModDependencyStatus.Sorted;
+            }
+
+            // missing required dependencies, mark failed
+            {
+                string[] missingModIDs =
+                    (
+                        from dependency in mod.Manifest.Dependencies
+                        where mods.All(m => m.Manifest.UniqueID != dependency.UniqueID)
+                        orderby dependency.UniqueID
+                        select dependency.UniqueID
+                    )
+                    .ToArray();
+                if (missingModIDs.Any())
+                {
+                    sortedMods.Push(mod);
+                    mod.SetStatus(ModMetadataStatus.Failed, $"it requires mods which aren't installed ({string.Join(", ", missingModIDs)}).");
+                    return states[mod] = ModDependencyStatus.Failed;
+                }
+            }
+
+            // process dependencies
+            {
+                states[mod] = ModDependencyStatus.Checking;
+
+                // get mods to load first
+                IModMetadata[] modsToLoadFirst =
+                    (
+                        from other in mods
+                        where mod.Manifest.Dependencies.Any(required => required.UniqueID == other.Manifest.UniqueID)
+                        select other
+                    )
+                    .ToArray();
+
+                // recursively sort dependencies
+                foreach (IModMetadata requiredMod in modsToLoadFirst)
+                {
+                    var subchain = new List<IModMetadata>(currentChain) { mod };
+
+                    // detect dependency loop
+                    if (states[requiredMod] == ModDependencyStatus.Checking)
+                    {
+                        sortedMods.Push(mod);
+                        mod.SetStatus(ModMetadataStatus.Failed, $"its dependencies have a circular reference: {string.Join(" => ", subchain.Select(p => p.DisplayName))} => {requiredMod.DisplayName}).");
+                        return states[mod] = ModDependencyStatus.Failed;
+                    }
+
+                    // recursively process each dependency
+                    var substatus = this.ProcessDependencies(mods, requiredMod, states, sortedMods, subchain);
+                    switch (substatus)
+                    {
+                        // sorted successfully
+                        case ModDependencyStatus.Sorted:
+                            break;
+
+                        // failed, which means this mod can't be loaded either
+                        case ModDependencyStatus.Failed:
+                            sortedMods.Push(mod);
+                            mod.SetStatus(ModMetadataStatus.Failed, $"it needs the '{requiredMod.DisplayName}' mod, which couldn't be loaded.");
+                            return states[mod] = ModDependencyStatus.Failed;
+
+                        // unexpected status
+                        case ModDependencyStatus.Queued:
+                        case ModDependencyStatus.Checking:
+                            throw new InvalidModStateException($"Something went wrong sorting dependencies: mod '{requiredMod.DisplayName}' unexpectedly stayed in the '{substatus}' status.");
+
+                        // sanity check
+                        default:
+                            throw new InvalidModStateException($"Unknown dependency status '{states[mod]}'.");
+                    }
+                }
+
+                // all requirements sorted successfully
+                sortedMods.Push(mod);
+                return states[mod] = ModDependencyStatus.Sorted;
+            }
+        }
+#endif
+
+        /// <summary>Get all mod folders in a root folder, passing through empty folders as needed.</summary>
+        /// <param name="rootPath">The root folder path to search.</param>
+        private IEnumerable<DirectoryInfo> GetModFolders(string rootPath)
+        {
+            foreach (string modRootPath in Directory.GetDirectories(rootPath))
+            {
+                DirectoryInfo directory = new DirectoryInfo(modRootPath);
+
+                // if a folder only contains another folder, check the inner folder instead
+                while (!directory.GetFiles().Any() && directory.GetDirectories().Length == 1)
+                    directory = directory.GetDirectories().First();
+
+                yield return directory;
+            }
+        }
+    }
+}