#nullable enable

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Runtime.Loader;

namespace ShrinkModFramework.Godot;

public sealed class ShrinkGodotModLoader : IDisposable
{
    private sealed record LoadedMod(AssemblyLoadContext LoadContext, WeakReference UnloadReference,
        ShrinkModContext Context, IReadOnlyList<IShrinkMod> Instances);
    private readonly Dictionary<string, LoadedMod> _loaded = new(StringComparer.OrdinalIgnoreCase);

    public IReadOnlyCollection<string> LoadedAssemblyPaths => _loaded.Keys;

    public IReadOnlyList<IShrinkMod> Load(string assemblyPath)
    {
        assemblyPath = Path.GetFullPath(assemblyPath);
        if (_loaded.ContainsKey(assemblyPath)) throw new InvalidOperationException($"Mod assembly is already loaded: {assemblyPath}");
        var loadContext = new AssemblyLoadContext($"ShrinkMod:{Path.GetFileNameWithoutExtension(assemblyPath)}", true);
        loadContext.Resolving += (_, name) => ResolveDependency(loadContext, Path.GetDirectoryName(assemblyPath)!, name);
        try
        {
            var assembly = loadContext.LoadFromAssemblyPath(assemblyPath);
            var entries = assembly.GetTypes().Where(type => !type.IsAbstract && typeof(IShrinkMod).IsAssignableFrom(type) &&
                type.GetCustomAttribute<ShrinkModAttribute>() != null).OrderBy(type => type.GetCustomAttribute<ShrinkModAttribute>()!.LoadOrder).ToArray();
            var context = new ShrinkModContext(Path.GetDirectoryName(assemblyPath)!);
            var instances = entries.Select(type => (IShrinkMod)(Activator.CreateInstance(type) ??
                throw new InvalidOperationException($"Failed to create mod entry: {type.FullName}"))).ToArray();
            foreach (var mod in instances) mod.OnConstruct(context);
            foreach (var mod in instances) mod.OnRegisterContent(context);
            foreach (var mod in instances) mod.OnInitialize(context);
            foreach (var mod in instances) mod.OnReady(context);
            _loaded[assemblyPath] = new LoadedMod(loadContext, new WeakReference(loadContext), context, instances);
            return instances;
        }
        catch { loadContext.Unload(); throw; }
    }

    public bool Unload(string assemblyPath)
    {
        assemblyPath = Path.GetFullPath(assemblyPath);
        if (!_loaded.Remove(assemblyPath, out var loaded)) return false;
        for (var index = loaded.Instances.Count - 1; index >= 0; index--)
            if (loaded.Instances[index] is IShrinkModUnload unload) unload.OnUnload(loaded.Context);
        loaded.LoadContext.Unload();
        return true;
    }

    public void Dispose()
    {
        foreach (var path in _loaded.Keys.ToArray()) Unload(path);
    }

    private static Assembly? ResolveDependency(AssemblyLoadContext context, string directory, AssemblyName name)
    {
        var shared = AssemblyLoadContext.Default.Assemblies.FirstOrDefault(assembly => assembly.GetName().Name == name.Name);
        if (shared != null) return shared;
        var path = Path.Combine(directory, name.Name + ".dll");
        return File.Exists(path) ? context.LoadFromAssemblyPath(path) : null;
    }
}