// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.IO;
using System.Threading;

namespace NuGet.Common.Migrations
{
    public static class MigrationRunner
    {
        private const string MaxMigrationFilename = "1";

        public static void Run()
        {
            Run(EnvironmentVariableWrapper.Instance);
        }

        internal static void Run(IEnvironmentVariableReader environmentVariableReader)
        {
            string migrationsDirectory = GetMigrationsDirectory(environmentVariableReader);

            Run(migrationsDirectory, environmentVariableReader);
        }

        internal static void Run(string migrationsDirectory, IEnvironmentVariableReader environmentVariableReader)
        {
            if (CommonEventSource.Instance.IsEnabled()) CommonEventSource.Instance.MigrationRunner_RunStart();

            var migrationPerformed = false;
            var expectedMigrationFilename = Path.Combine(migrationsDirectory, MaxMigrationFilename);

            try
            {
                if (!File.Exists(expectedMigrationFilename))
                {
                    // Multiple processes or threads might be trying to call this concurrently (especially via NuGetSdkResolver)
                    // so use a global mutex and then check if someone else already did the work.
                    using (var mutex = new Mutex(false, "NuGet-Migrations"))
                    {
                        if (WaitForMutex(mutex))
                        {
                            try
                            {
                                Directory.CreateDirectory(migrationsDirectory);

                                // Only run migrations that have not already been run
                                if (!File.Exists(expectedMigrationFilename))
                                {
                                    migrationPerformed = true;

                                    Migration1.Run(environmentVariableReader);
                                    // Create file for the migration run, so that if an older version of NuGet is run, it doesn't try to run migrations again.
                                    File.WriteAllText(expectedMigrationFilename, string.Empty);
                                }
                            }
                            catch { }
                            finally
                            {
                                mutex.ReleaseMutex();
                            }
                        }
                    }
                }
            }
            finally
            {
                if (CommonEventSource.Instance.IsEnabled()) CommonEventSource.Instance.MigrationRunner_RunStop(expectedMigrationFilename, migrationPerformed ? 1 : 0);
            }

            static bool WaitForMutex(Mutex mutex)
            {
                bool captured;

                try
                {
                    captured = mutex.WaitOne(TimeSpan.FromMinutes(1), false);
                }
                catch (AbandonedMutexException)
                {
                    captured = true;
                }

                return captured;
            }
        }

        internal static string GetMigrationsDirectory(IEnvironmentVariableReader environmentVariableReader)
        {
            if (RuntimeEnvironmentHelper.IsWindows)
            {
                return Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "NuGet", "Migrations");
            }

            var XdgDataHome = environmentVariableReader.GetEnvironmentVariable("XDG_DATA_HOME");

            return string.IsNullOrEmpty(XdgDataHome)
                ? Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.UserProfile), ".local", "share", "NuGet", "Migrations")
                : Path.Combine(XdgDataHome, "NuGet", "Migrations");
        }
    }
}