LastSyncedFileManager.cs

using System.Globalization;
using Umbraco.Cms.Core.Hosting;
using Umbraco.Extensions;

namespace Umbraco.Cms.Infrastructure.Sync;

public sealed class LastSyncedFileManager
{
    private readonly IHostingEnvironment _hostingEnvironment;
    private string? _distCacheFile;
    private int _lastId;
    private object? _lastIdLock;
    private bool _lastIdReady;

    public LastSyncedFileManager(IHostingEnvironment hostingEnvironment)
        => _hostingEnvironment = hostingEnvironment;

    /// <summary>
    ///     Returns the last-synced id.
    /// </summary>
    public int LastSyncedId => LazyInitializer.EnsureInitialized(
        ref _lastId,
        ref _lastIdReady,
        ref _lastIdLock,
        () =>
        {
            // On first load, read from file, else it will return the in-memory _lastId value
            var distCacheFilePath = DistCacheFilePath;

            if (File.Exists(distCacheFilePath))
            {
                var content = File.ReadAllText(distCacheFilePath);
                if (int.TryParse(content, NumberStyles.Integer, CultureInfo.InvariantCulture, out var last))
                {
                    return last;
                }
            }

            return -1;
        });

    /// <summary>
    ///     Gets the dist cache file path (once).
    /// </summary>
    /// <returns></returns>
    public string DistCacheFilePath => LazyInitializer.EnsureInitialized(ref _distCacheFile, () =>
    {
        var fileName = (Environment.MachineName + _hostingEnvironment.ApplicationId).GenerateHash() + "-lastsynced.txt";

        var distCacheFilePath = Path.Combine(_hostingEnvironment.LocalTempPath, "DistCache", fileName);

        // ensure the folder exists
        var folder = Path.GetDirectoryName(distCacheFilePath);
        if (folder == null)
        {
            throw new InvalidOperationException("The folder could not be determined for the file " + distCacheFilePath);
        }

        if (Directory.Exists(folder) == false)
        {
            Directory.CreateDirectory(folder);
        }

        return distCacheFilePath;
    });

    /// <summary>
    ///     Persists the last-synced id to file.
    /// </summary>
    /// <param name="id">The id.</param>
    public void SaveLastSyncedId(int id)
    {
        if (_lastIdLock is null)
        {
            return;
        }

        lock (_lastIdLock)
        {
            if (!_lastIdReady)
            {
                throw new InvalidOperationException("Cannot save the last synced id before it is read");
            }

            File.WriteAllText(DistCacheFilePath, id.ToString(CultureInfo.InvariantCulture));
            _lastId = id;
        }
    }
}