jRay/Jellyfin.Plugin.JRay/Services/ManagedTruthStore.cs

using System;
using System.IO;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;
using Jellyfin.Plugin.JRay.Models;
using Jellyfin.Plugin.JRay.Services.Interfaces;
using MediaBrowser.Common.Configuration;
using Microsoft.Extensions.Logging;

namespace Jellyfin.Plugin.JRay.Services;

/// <summary>
/// Stores truth files pushed directly to JRay (e.g. by a remote extraction
/// worker) under the plugin's configuration directory, keyed by item id.
/// </summary>
/// <remarks>
/// Deliberately outside the media library filesystem, so a worker that cannot
/// write beside the media file is not a second-class producer.
/// </remarks>
// TRACES: JR-009, JR-010 | PR-004
public sealed class ManagedTruthStore : IManagedTruthStore
{
    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web);

    private readonly IApplicationPaths _applicationPaths;
    private readonly ILogger<ManagedTruthStore> _logger;

    /// <summary>
    /// Initializes a new instance of the <see cref="ManagedTruthStore"/> class.
    /// </summary>
    /// <param name="applicationPaths">The Jellyfin application paths.</param>
    /// <param name="logger">The logger.</param>
    public ManagedTruthStore(IApplicationPaths applicationPaths, ILogger<ManagedTruthStore> logger)
    {
        _applicationPaths = applicationPaths;
        _logger = logger;
    }

    /// <inheritdoc />
    public async Task<TruthFile?> LoadAsync(Guid itemId, CancellationToken cancellationToken)
    {
        var path = GetPath(itemId);
        if (!File.Exists(path))
        {
            return null;
        }

        try
        {
            using var stream = File.OpenRead(path);
            var truth = await JsonSerializer.DeserializeAsync<TruthFile>(stream, JsonOptions, cancellationToken)
                .ConfigureAwait(false);

            // Managed truth is checked on the way out as well as on the way in.
            // Data written by an earlier plugin version is already on disk, and
            // it did not pass today's PUT.
            if (!TruthSchema.IsSupported(truth))
            {
                _logger.LogWarning(
                    "JRay: ignoring managed truth {Path} — schema_version {Found}, expected {Expected}. Re-push or re-extract this item.",
                    path,
                    truth?.SchemaVersion ?? 0,
                    TruthSchema.SupportedVersion);
                return null;
            }

            return truth;
        }
        catch (Exception ex) when (ex is IOException or JsonException)
        {
            _logger.LogWarning(
                ex,
                "JRay: failed to read managed truth file {Path}. If this is v1 data, re-push it — v1 is no longer read.",
                path);
            return null;
        }
    }

    /// <inheritdoc />
    public async Task SaveAsync(Guid itemId, TruthFile truth, TruthProvenance provenance, CancellationToken cancellationToken)
    {
        var path = GetPath(itemId);
        var directory = Path.GetDirectoryName(path) ?? throw new InvalidOperationException("Managed truth path has no directory.");
        Directory.CreateDirectory(directory);

        var tempPath = path + ".tmp";
        using (var stream = File.Create(tempPath))
        {
            await JsonSerializer.SerializeAsync(stream, truth, JsonOptions, cancellationToken).ConfigureAwait(false);
        }

        File.Move(tempPath, path, overwrite: true);

        // Written after the truth file, so a crash between the two leaves truth
        // with no provenance (readable, source unknown) rather than provenance
        // describing a file that is not there.
        var provenancePath = GetProvenancePath(itemId);
        var provenanceTemp = provenancePath + ".tmp";
        using (var stream = File.Create(provenanceTemp))
        {
            await JsonSerializer.SerializeAsync(stream, provenance, JsonOptions, cancellationToken).ConfigureAwait(false);
        }

        File.Move(provenanceTemp, provenancePath, overwrite: true);
    }

    /// <inheritdoc />
    public TruthProvenance? LoadProvenance(Guid itemId)
    {
        var path = GetProvenancePath(itemId);
        if (!File.Exists(path))
        {
            return null;
        }

        try
        {
            using var stream = File.OpenRead(path);
            return JsonSerializer.Deserialize<TruthProvenance>(stream, JsonOptions);
        }
        catch (Exception ex) when (ex is IOException or JsonException)
        {
            // Provenance is metadata about the claim, not the claim. Losing it
            // must never make readable truth data unreadable.
            _logger.LogWarning(ex, "JRay: failed to read truth provenance at {Path}", path);
            return null;
        }
    }

    /// <inheritdoc />
    public bool Delete(Guid itemId)
    {
        var provenancePath = GetProvenancePath(itemId);
        if (File.Exists(provenancePath))
        {
            File.Delete(provenancePath);
        }

        var path = GetPath(itemId);
        if (!File.Exists(path))
        {
            return false;
        }

        File.Delete(path);
        return true;
    }

    /// <inheritdoc />
    public bool Exists(Guid itemId)
    {
        return File.Exists(GetPath(itemId));
    }

    private string GetPath(Guid itemId)
    {
        return Path.Combine(_applicationPaths.PluginConfigurationsPath, "JRay", "truth", itemId.ToString("D") + ".json");
    }

    private string GetProvenancePath(Guid itemId)
    {
        return Path.Combine(_applicationPaths.PluginConfigurationsPath, "JRay", "truth", itemId.ToString("D") + ".provenance.json");
    }
}