// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

#if FEATURE_APPDOMAIN
using System;
using System.Reflection;
using Microsoft.Build.Shared.Debugging;
#endif
using Microsoft.Build.Framework;

namespace Microsoft.Build.Shared;

/// <summary>
/// Class for loading tasks
/// </summary>
internal static class TaskLoader
{
#if FEATURE_APPDOMAIN
    /// <summary>
    /// For saving the assembly that was loaded by the TypeLoader
    /// We only use this when the assembly failed to load properly into the appdomain
    /// </summary>
    private static LoadedType? s_resolverLoadedType;
#endif

    /// <summary>
    /// Delegate for logging task loading errors.
    /// </summary>
    internal delegate void LogError(string taskLocation, int taskLine, int taskColumn, string message, params object[] messageArgs);

    /// <summary>
    /// Creates an ITask instance and returns it.
    /// </summary>
#pragma warning disable SA1111, SA1009 // Closing parenthesis should be on line of last parameter
    internal static ITask? CreateTask(
        LoadedType loadedType,
        string taskName,
        string taskLocation,
        int taskLine,
        int taskColumn,
        LogError logError,
        TaskEnvironment? taskEnvironment,
#if FEATURE_APPDOMAIN
        AppDomainSetup appDomainSetup,
        Action<AppDomain> appDomainCreated,
#endif
        bool isOutOfProc
#if FEATURE_APPDOMAIN
        , out AppDomain? taskAppDomain
#endif
        )
#pragma warning restore SA1111, SA1009 // Closing parenthesis should be on line of last parameter
    {
#if FEATURE_APPDOMAIN
        bool separateAppDomain = loadedType.HasLoadInSeparateAppDomainAttribute;
        s_resolverLoadedType = null;
        taskAppDomain = null;
        ITask? taskInstanceInOtherAppDomain = null;
#endif

        try
        {
#if FEATURE_APPDOMAIN
            if (separateAppDomain)
            {
                if (!loadedType.IsMarshalByRef)
                {
                    logError(
                        taskLocation,
                        taskLine,
                        taskColumn,
                        "TaskNotMarshalByRef",
                        taskName);

                    return null;
                }
                else
                {
                    // Our task depend on this name to be precisely that, so if you change it make sure
                    // you also change the checks in the tasks run in separate AppDomains. Better yet, just don't change it.

                    // Make sure we copy the appdomain configuration and send it to the appdomain we create so that if the creator of the current appdomain
                    // has done the binding redirection in code, that we will get those settings as well.
                    AppDomainSetup appDomainInfo = new AppDomainSetup();

                    // Get the current app domain setup settings
                    byte[] currentAppdomainBytes = appDomainSetup.GetConfigurationBytes();

                    // Apply the appdomain settings to the new appdomain before creating it
                    appDomainInfo.SetConfigurationBytes(currentAppdomainBytes);

                    if (BuildEnvironmentHelper.Instance.RunningTests)
                    {
                        // Prevent the new app domain from looking in the VS test runner location. If this
                        // is not done, we will not be able to find Microsoft.Build.* assemblies.
                        appDomainInfo.ApplicationBase = BuildEnvironmentHelper.Instance.CurrentMSBuildToolsDirectory;
                        appDomainInfo.ConfigurationFile = BuildEnvironmentHelper.Instance.CurrentMSBuildConfigurationFile;
                    }

                    AppDomain.CurrentDomain.AssemblyResolve += AssemblyResolver;
                    s_resolverLoadedType = loadedType;

                    taskAppDomain = AppDomain.CreateDomain(isOutOfProc ? "taskAppDomain (out-of-proc)" : "taskAppDomain (in-proc)", null, appDomainInfo);

                    if (loadedType.LoadedAssembly != null)
                    {
                        taskAppDomain.Load(loadedType.LoadedAssemblyName);
                    }

                    // Hook up last minute dumping of any exceptions
                    taskAppDomain.UnhandledException += DebugUtils.UnhandledExceptionHandler;
                    appDomainCreated?.Invoke(taskAppDomain);
                }
            }
            else
#endif
            {
                // perf improvement for the same appdomain case - we already have the type object
                // and don't want to go through reflection to recreate it from the name.
                // LoadedType owns instantiation: it invokes the TaskEnvironment-accepting constructor when
                // the task declares one (so the task can compute environment-dependent defaults during
                // construction) or the parameterless one otherwise, through a cached, Native AOT friendly
                // mechanism. The engine still assigns the TaskEnvironment property separately afterward.
                return loadedType.CreateInstance(taskEnvironment);
            }

#if FEATURE_APPDOMAIN
            if (loadedType.Assembly.AssemblyFile != null)
            {
                taskInstanceInOtherAppDomain = (ITask)taskAppDomain.CreateInstanceFromAndUnwrap(loadedType.Assembly.AssemblyFile, loadedType.Type.FullName);

                // this will force evaluation of the task class type and try to load the task assembly
                Type taskType = taskInstanceInOtherAppDomain.GetType();

                // If the types don't match, we have a problem. It means that our AppDomain was able to load
                // a task assembly using Load, and loaded a different one. I don't see any other choice than
                // to fail here.
                if (taskType != loadedType.Type)
                {
                    logError(
                    taskLocation,
                    taskLine,
                    taskColumn,
                    "ConflictingTaskAssembly",
                    loadedType.Assembly.AssemblyFile,
                    loadedType.Type.Assembly.Location);

                    taskInstanceInOtherAppDomain = null;
                }
            }
            else
            {
                taskInstanceInOtherAppDomain = (ITask)taskAppDomain.CreateInstanceAndUnwrap(loadedType.Type.Assembly.FullName, loadedType.Type.FullName);
            }

            return  taskInstanceInOtherAppDomain;
#endif
        }
        finally
        {
#if FEATURE_APPDOMAIN
            // Don't leave appdomains open
            if (taskAppDomain != null && taskInstanceInOtherAppDomain == null)
            {
                AppDomain.Unload(taskAppDomain);
                RemoveAssemblyResolver();
            }
#endif
        }
    }

#if FEATURE_APPDOMAIN
    /// <summary>
    /// This is a resolver to help created AppDomains when they are unable to load an assembly into their domain we will help
    /// them succeed by providing the already loaded one in the currentdomain so that they can derive AssemblyName info from it
    /// </summary>
    internal static Assembly? AssemblyResolver(object sender, ResolveEventArgs args)
    {
        if (args.Name.Equals(s_resolverLoadedType?.LoadedAssemblyName?.FullName, StringComparison.OrdinalIgnoreCase))
        {
            if (s_resolverLoadedType == null || s_resolverLoadedType.Path == null)
            {
                return null;
            }
            return s_resolverLoadedType.LoadedAssembly ?? Assembly.Load(s_resolverLoadedType.Path);
        }

        return null;
    }

    /// <summary>
    /// Check if we added a resolver and remove it
    /// </summary>
    internal static void RemoveAssemblyResolver()
    {
        if (s_resolverLoadedType != null)
        {
            AppDomain.CurrentDomain.AssemblyResolve -= AssemblyResolver;
            s_resolverLoadedType = null;
        }
    }
#endif
}