using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using BepInEx.Logging;
using Mono.Cecil;

namespace BepInEx.Preloader.Patcher
{
    /// <summary>
    ///     Delegate used in patching assemblies.
    /// </summary>
    /// <param name="assembly">The assembly that is being patched.</param>
    internal delegate void AssemblyPatcherDelegate(ref AssemblyDefinition assembly);

    /// <summary>
    ///     Worker class which is used for loading and patching entire folders of assemblies, or alternatively patching and
    ///     loading assemblies one at a time.
    /// </summary>
    internal static class AssemblyPatcher
    {
        private static readonly List<PatcherPlugin> patchers = new List<PatcherPlugin>();

        /// <summary>
        ///     Configuration value of whether assembly dumping is enabled or not.
        /// </summary>
        private static bool DumpingEnabled =>
            Utility.SafeParseBool(Config.GetEntry("dump-assemblies", "false", "Preloader"));

        /// <summary>
        ///     Adds a single assembly patcher to the pool of applicable patches.
        /// </summary>
        /// <param name="patcher">Patcher to apply.</param>
        public static void AddPatcher(PatcherPlugin patcher)
        {
            patchers.Add(patcher);
        }

        /// <summary>
        ///     Adds all patchers from all managed assemblies specified in a directory.
        /// </summary>
        /// <param name="directory">Directory to search patcher DLLs from.</param>
        /// <param name="patcherLocator">A function that locates assembly patchers in a given managed assembly.</param>
        public static void AddPatchersFromDirectory(string directory,
            Func<Assembly, List<PatcherPlugin>> patcherLocator)
        {
            if (!Directory.Exists(directory))
                return;

            var sortedPatchers = new SortedDictionary<string, PatcherPlugin>();

            foreach (string assemblyPath in Directory.GetFiles(directory, "*.dll"))
                try
                {
                    var assembly = Assembly.LoadFrom(assemblyPath);

                    foreach (var patcher in patcherLocator(assembly))
                        sortedPatchers.Add(patcher.Name, patcher);
                }
                catch (BadImageFormatException)
                {
                } //unmanaged DLL
                catch (ReflectionTypeLoadException)
                {
                } //invalid references

            foreach (KeyValuePair<string, PatcherPlugin> patcher in sortedPatchers)
                AddPatcher(patcher.Value);
        }

        private static void InitializePatchers()
        {
            foreach (var assemblyPatcher in patchers)
                assemblyPatcher.Initializer?.Invoke();
        }

        private static void FinalizePatching()
        {
            foreach (var assemblyPatcher in patchers)
                assemblyPatcher.Finalizer?.Invoke();
        }

        /// <summary>
        ///     Releases all patchers to let them be collected by GC.
        /// </summary>
        public static void DisposePatchers()
        {
            patchers.Clear();
        }

        /// <summary>
        ///     Applies patchers to all assemblies in the given directory and loads patched assemblies into memory.
        /// </summary>
        /// <param name="directory">Directory to load CLR assemblies from.</param>
        public static void PatchAndLoad(string directory)
        {
            // First, load patchable assemblies into Cecil
            var assemblies = new Dictionary<string, AssemblyDefinition>();

            foreach (string assemblyPath in Directory.GetFiles(directory, "*.dll"))
            {
                var assembly = AssemblyDefinition.ReadAssembly(assemblyPath);

                //NOTE: this is special cased here because the dependency handling for System.dll is a bit wonky
                //System has an assembly reference to itself, and it also has a reference to Mono.Security causing a circular dependency
                //It's also generally dangerous to change system.dll since so many things rely on it, 
                // and it's already loaded into the appdomain since this loader references it, so we might as well skip it
                if (assembly.Name.Name == "System"
                    || assembly.Name.Name == "mscorlib"
                ) //mscorlib is already loaded into the appdomain so it can't be patched
                {
                    assembly.Dispose();
                    continue;
                }

                if (UnityPatches.AssemblyLocations.ContainsKey(assembly.FullName))
                {
                    Logger.Log(LogLevel.Warning,
                        $"Tried to load duplicate assembly {Path.GetFileName(assemblyPath)} from Managed folder! Skipping...");
                    continue;
                }

                assemblies.Add(Path.GetFileName(assemblyPath), assembly);
                UnityPatches.AssemblyLocations.Add(assembly.FullName, Path.GetFullPath(assemblyPath));
            }

            // Next, initialize all the patchers
            InitializePatchers();

            // Then, perform the actual patching
            var patchedAssemblies = new HashSet<string>();
            foreach (var assemblyPatcher in patchers)
            foreach (string targetDll in assemblyPatcher.TargetDLLs)
                if (assemblies.TryGetValue(targetDll, out var assembly))
                {
                    assemblyPatcher.Patcher?.Invoke(ref assembly);
                    assemblies[targetDll] = assembly;
                    patchedAssemblies.Add(targetDll);
                }

            // Finally, load all assemblies into memory
            foreach (KeyValuePair<string, AssemblyDefinition> kv in assemblies)
            {
                string filename = kv.Key;
                var assembly = kv.Value;

                if (DumpingEnabled && patchedAssemblies.Contains(filename))
                    using (var mem = new MemoryStream())
                    {
                        string dirPath = Path.Combine(Paths.PluginPath, "DumpedAssemblies");

                        if (!Directory.Exists(dirPath))
                            Directory.CreateDirectory(dirPath);

                        assembly.Write(mem);
                        File.WriteAllBytes(Path.Combine(dirPath, filename), mem.ToArray());
                    }

                Load(assembly);
                assembly.Dispose();
            }

            //run all finalizers
            FinalizePatching();
        }

        /// <summary>
        ///     Loads an individual assembly defintion into the CLR.
        /// </summary>
        /// <param name="assembly">The assembly to load.</param>
        public static void Load(AssemblyDefinition assembly)
        {
            using (var assemblyStream = new MemoryStream())
            {
                assembly.Write(assemblyStream);
                Assembly.Load(assemblyStream.ToArray());
            }
        }
    }
}