LightlessClient/LightlessSync/LightlessConfiguration/ConfigurationSaveService.cs

using LightlessSync.LightlessConfiguration.Configurations;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using System.Reflection;
using System.Text.Json;

namespace LightlessSync.LightlessConfiguration;

public class ConfigurationSaveService : IHostedService
{
    private readonly HashSet<object> _configsToSave = [];
    private readonly ILogger<ConfigurationSaveService> _logger;
    private readonly SemaphoreSlim _configSaveSemaphore = new(1, 1);
    private readonly CancellationTokenSource _configSaveCheckCts = new();
    public const string BackupFolder = "config_backup";
    private readonly MethodInfo _saveMethod;

    public ConfigurationSaveService(ILogger<ConfigurationSaveService> logger, IEnumerable<IConfigService<ILightlessConfiguration>> configs)
    {
        foreach (var config in configs)
        {
            config.ConfigSave += OnConfigurationSave;
        }
        _logger = logger;
#pragma warning disable S3011 // Reflection should not be used to increase accessibility of classes, methods, or fields
        _saveMethod = GetType().GetMethod(nameof(SaveConfig), BindingFlags.Instance | BindingFlags.NonPublic)!;
#pragma warning restore S3011 // Reflection should not be used to increase accessibility of classes, methods, or fields
    }

    private void OnConfigurationSave(object? sender, EventArgs e)
    {
        _configSaveSemaphore.Wait();
        _configsToSave.Add(sender!);
        _configSaveSemaphore.Release();
    }

    private async Task PeriodicSaveCheck(CancellationToken ct)
    {
        while (!ct.IsCancellationRequested)
        {
            try
            {
                await SaveConfigs().ConfigureAwait(false);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Error during SaveConfigs");
            }

            await Task.Delay(TimeSpan.FromSeconds(5), ct).ConfigureAwait(false);
        }
    }

    private async Task SaveConfigs()
    {
        if (_configsToSave.Count == 0) return;

        await _configSaveSemaphore.WaitAsync().ConfigureAwait(false);
        var configList = _configsToSave.ToList();
        _configsToSave.Clear();
        _configSaveSemaphore.Release();

        foreach (var config in configList)
        {
            var expectedType = config.GetType().BaseType!.GetGenericArguments()[0];
            var save = _saveMethod.MakeGenericMethod(expectedType);
            await ((Task)save.Invoke(this, [config])!).ConfigureAwait(false);
        }
    }

    private async Task SaveConfig<T>(IConfigService<T> config) where T : ILightlessConfiguration
    {
        _logger.LogTrace("Saving {configName}", config.ConfigurationName);
        var configDir = config.ConfigurationPath.Replace(config.ConfigurationName, string.Empty);
        var isTempCollections = string.Equals(config.ConfigurationName, TempCollectionConfigService.ConfigName, StringComparison.OrdinalIgnoreCase);

        if (!isTempCollections)
        {
            try
            {
                var configBackupFolder = Path.Join(configDir, BackupFolder);
                if (!Directory.Exists(configBackupFolder))
                    Directory.CreateDirectory(configBackupFolder);

                var configNameSplit = config.ConfigurationName.Split(".");
                var existingConfigs = Directory.EnumerateFiles(
                    configBackupFolder,
                    configNameSplit[0] + "*")
                    .Select(c => new FileInfo(c))
                    .OrderByDescending(c => c.LastWriteTime).ToList();
                if (existingConfigs.Skip(10).Any())
                {
                    foreach (var oldBak in existingConfigs.Skip(10).ToList())
                    {
                        oldBak.Delete();
                    }
                }

                string backupPath = Path.Combine(configBackupFolder, configNameSplit[0] + "." + DateTime.Now.ToString("yyyyMMddHHmmss") + "." + configNameSplit[1]);
                _logger.LogTrace("Backing up current config to {backupPath}", backupPath);
                File.Copy(config.ConfigurationPath, backupPath, overwrite: true);
                FileInfo fi = new(backupPath);
                fi.LastWriteTimeUtc = DateTime.UtcNow;
            }
            catch (Exception ex)
            {
                // ignore if file cannot be backupped
                _logger.LogWarning(ex, "Could not create backup for {config}", config.ConfigurationPath);
            }
        }

        var temp = config.ConfigurationPath + ".tmp";
        try
        {
            await File.WriteAllTextAsync(temp, JsonSerializer.Serialize(config.Current, typeof(T), new JsonSerializerOptions()
            {
                WriteIndented = !isTempCollections
            })).ConfigureAwait(false);
            File.Move(temp, config.ConfigurationPath, true);
            config.UpdateLastWriteTime();
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "Error during config save of {config}", config.ConfigurationName);
        }
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        _ = Task.Run(() => PeriodicSaveCheck(_configSaveCheckCts.Token));
        return Task.CompletedTask;
    }

    public async Task StopAsync(CancellationToken cancellationToken)
    {
        await _configSaveCheckCts.CancelAsync().ConfigureAwait(false);
        _configSaveCheckCts.Dispose();

        await SaveConfigs().ConfigureAwait(false);
    }
}