Vocaluxe/VocaluxeSongServer/Library/CLibraryIndex.cs

using Microsoft.Extensions.Options;

namespace VocaluxeSongServer.Library
{
    public sealed class CLibraryOptions
    {
        /// <summary>Root folder of the song library (in Docker: the mounted share, default /songs).</summary>
        public string Path { get; set; } = "/songs";
        /// <summary>Minutes between automatic rescans. 0 = only at startup and via POST /api/v1/library/rescan.</summary>
        public int ScanIntervalMinutes { get; set; } = 10;
        /// <summary>If set, every /api request needs the header X-Api-Key with this value.</summary>
        public string ApiKey { get; set; } = "";
    }

    /// <summary>Holds the current library snapshot and rescans it in the background.</summary>
    public sealed class CLibraryIndex : BackgroundService
    {
        private readonly CLibraryScanner _Scanner;
        private readonly CLibraryOptions _Options;
        private readonly ILogger<CLibraryIndex> _Logger;
        private readonly SemaphoreSlim _ScanLock = new(1, 1);
        private readonly SemaphoreSlim _RescanRequested = new(0, 1);
        private volatile CLibrarySnapshot? _Current;

        public CLibraryIndex(CLibraryScanner scanner, IOptions<CLibraryOptions> options, ILogger<CLibraryIndex> logger)
        {
            _Scanner = scanner;
            _Options = options.Value;
            _Logger = logger;
        }

        /// <summary>The last completed scan, or null while the first scan is running.</summary>
        public CLibrarySnapshot? Current => _Current;

        public string Root => System.IO.Path.GetFullPath(_Options.Path);

        /// <summary>Asks for a rescan as soon as possible (returns immediately).</summary>
        public void RequestRescan()
        {
            if (_RescanRequested.CurrentCount == 0)
            {
                try
                {
                    _RescanRequested.Release();
                }
                catch (SemaphoreFullException)
                {
                    // Already requested.
                }
            }
        }

        public async Task ScanNowAsync(CancellationToken ct = default)
        {
            await _ScanLock.WaitAsync(ct);
            try
            {
                if (!Directory.Exists(Root))
                {
                    _Logger.LogError("Library folder {Root} does not exist", Root);
                    return;
                }

                var started = DateTime.UtcNow;
                var snapshot = await Task.Run(() => _Scanner.Scan(Root), ct);
                var changed = _Current?.Dto.Version != snapshot.Dto.Version;
                _Current = snapshot;
                _Logger.LogInformation("Scanned {Root}: {Songs} songs, {Files} files in {Seconds:0.0} s{Changed}", Root,
                    snapshot.Dto.Songs.Count, snapshot.Dto.Files.Count, (DateTime.UtcNow - started).TotalSeconds, changed ? "" : " (unchanged)");
            }
            finally
            {
                _ScanLock.Release();
            }
        }

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                try
                {
                    await ScanNowAsync(stoppingToken);
                }
                catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
                {
                    return;
                }
                catch (Exception e)
                {
                    _Logger.LogError(e, "Library scan failed");
                }

                var interval = _Options.ScanIntervalMinutes > 0 ? TimeSpan.FromMinutes(_Options.ScanIntervalMinutes) : Timeout.InfiniteTimeSpan;
                try
                {
                    await _RescanRequested.WaitAsync(interval, stoppingToken);
                }
                catch (OperationCanceledException)
                {
                    return;
                }
            }
        }
    }
}