// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
#nullable disable
 
#if NETCOREAPP
 
using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using System.Runtime.Loader;
 
namespace AnalyzerRunner
{
    internal static class LooseVersionAssemblyLoader
    {
        private static readonly Dictionary<string, Assembly> s_pathsToAssemblies = new Dictionary<string, Assembly>(StringComparer.OrdinalIgnoreCase);
        private static readonly Dictionary<string, Assembly> s_namesToAssemblies = new Dictionary<string, Assembly>();
 
        private static readonly object s_guard = new object();
        private static readonly string[] s_extensions = new[] { "ni.dll", "ni.exe", "dll", "exe" };
 
        /// <summary>
        /// Register an assembly loader that will load assemblies with higher version than what was requested.
        /// </summary>
        public static void Register(string searchPath)
        {
            AssemblyLoadContext.Default.Resolving += (AssemblyLoadContext context, AssemblyName assemblyName) =>
            {
                lock (s_guard)
                {
                    if (s_namesToAssemblies.TryGetValue(assemblyName.FullName, out var assembly))
                    {
                        return assembly;
                    }
 
                    return TryResolveAssemblyFromPaths_NoLock(context, assemblyName, searchPath);
                }
            };
        }
 
        private static Assembly TryResolveAssemblyFromPaths_NoLock(AssemblyLoadContext context, AssemblyName assemblyName, string searchPath)
        {
            foreach (var cultureSubfolder in string.IsNullOrEmpty(assemblyName.CultureName)
                // If no culture is specified, attempt to load directly from
                // the known dependency paths.
                ? new[] { string.Empty }
                // Search for satellite assemblies in culture subdirectories
                // of the assembly search directories, but fall back to the
                // bare search directory if that fails.
                : new[] { assemblyName.CultureName, string.Empty })
            {
                foreach (var extension in s_extensions)
                {
                    var candidatePath = Path.Combine(
                        searchPath, cultureSubfolder, $"{assemblyName.Name}.{extension}");
 
                    var isAssemblyLoaded = s_pathsToAssemblies.ContainsKey(candidatePath);
                    if (isAssemblyLoaded || !File.Exists(candidatePath))
                    {
                        continue;
                    }
 
                    var candidateAssemblyName = AssemblyLoadContext.GetAssemblyName(candidatePath);
                    if (candidateAssemblyName.Version < assemblyName.Version)
                    {
                        continue;
                    }
 
                    return LoadAndCache_NoLock(context, candidatePath);
                }
            }
 
            return null;
        }
 
        private static Assembly LoadAndCache_NoLock(AssemblyLoadContext context, string fullPath)
        {
            var assembly = context.LoadFromAssemblyPath(fullPath);
            var name = assembly.FullName;
 
            s_pathsToAssemblies[fullPath] = assembly;
            s_namesToAssemblies[name] = assembly;
 
            return assembly;
        }
    }
}
 
#endif