feature: Opus format resolution + sidecar lookup contract (Phase 18.2)

2026-06-23 07:45:06 -04:00
parent e845dc3496
commit 19793ba1c3
5 changed files with 323 additions and 0 deletions
@@ -0,0 +1,23 @@
+using DeepDrftContent.FileDatabase.Models;
+using DeepDrftModels.Enums;
+
+namespace DeepDrftContent.Processors.Opus;
+
+/// <summary>
+/// The outcome of resolving a track + requested <see cref="AudioFormat"/> to a concrete artifact
+/// (Phase 18.2). Carries the bytes, the content-type that matches <em>what was actually returned</em>,
+/// and the format actually served — which may differ from the requested one when the C2 fallback fires
+/// (Opus requested, no Opus artifact → the lossless artifact + its content-type). The delivery layer
+/// (18.3) sets the response <c>Content-Type</c> from <see cref="ContentType"/> so the eventual decoder
+/// picks the right decoder for the bytes it receives, not the bytes the listener asked for.
+/// </summary>
+/// <param name="Audio">The resolved audio artifact (never null when a resolution succeeds).</param>
+/// <param name="ContentType">The MIME type of <paramref name="Audio"/> (e.g. <c>audio/ogg</c> for Opus,
+/// or the source's real MIME for lossless).</param>
+/// <param name="ResolvedFormat">The format actually returned. Equal to the requested format on a direct
+/// hit; <see cref="AudioFormat.Lossless"/> when an Opus request fell back.</param>
+public sealed record ResolvedAudio(AudioBinary Audio, string ContentType, AudioFormat ResolvedFormat)
+{
+    /// <summary>True when an Opus request was served the lossless artifact because no Opus existed (C2).</summary>
+    public bool DidFallBack(AudioFormat requested) => requested != ResolvedFormat;
+}
@@ -0,0 +1,91 @@
+using DeepDrftContent.Constants;
+using DeepDrftContent.FileDatabase.Models;
+using DeepDrftModels.Enums;
+using Microsoft.Extensions.Logging;
+using FileDb = DeepDrftContent.FileDatabase.Services.FileDatabase;
+
+namespace DeepDrftContent.Processors.Opus;
+
+/// <summary>
+/// The server-side format resolution + sidecar lookup seam (Phase 18.2). Given a track's
+/// <c>EntryKey</c> and a requested <see cref="AudioFormat"/>, returns the correct audio artifact and the
+/// content-type that matches it; given an <c>EntryKey</c>, returns the Opus seek/setup sidecar bytes.
+/// Downstream waves call this — 18.3 wires it behind the <c>?format=</c> stream param and serves the
+/// sidecar over HTTP; this wave delivers only the seam, not the HTTP surface.
+/// <para>
+/// Additive and non-breaking (C2): the lossless branch reads the source exactly as the existing stream
+/// path does (via <see cref="TrackContentService.GetAudioBinaryAsync"/>), and an Opus request for a track
+/// with no Opus artifact falls back to lossless rather than failing. Mirrors the
+/// <see cref="WaveformProfileService"/> derived-artifact lookup precedent: read from the dedicated vault,
+/// swallow misses to null (FileDatabase convention), let the caller decide.
+/// </para>
+/// </summary>
+public sealed class TrackFormatResolver
+{
+    private readonly FileDb _fileDatabase;
+    private readonly TrackContentService _trackContentService;
+    private readonly ILogger<TrackFormatResolver> _logger;
+
+    public TrackFormatResolver(
+        FileDb fileDatabase,
+        TrackContentService trackContentService,
+        ILogger<TrackFormatResolver> logger)
+    {
+        _fileDatabase = fileDatabase;
+        _trackContentService = trackContentService;
+        _logger = logger;
+    }
+
+    /// <summary>
+    /// Resolves <paramref name="entryKey"/> + <paramref name="requestedFormat"/> to the audio artifact to
+    /// serve plus its content-type. <see cref="AudioFormat.Lossless"/> resolves the source artifact in the
+    /// <c>tracks</c> vault with its real MIME (WAV/MP3/FLAC). <see cref="AudioFormat.Opus"/> resolves the
+    /// derived Opus artifact (<c>audio/ogg</c>) when present, and <strong>falls back to lossless</strong>
+    /// when it is not (C2). Returns null only when even the lossless source is missing — i.e. the track has
+    /// no audio at all (an unknown key or a genuinely empty vault), the one case the caller treats as 404.
+    /// </summary>
+    public async Task<ResolvedAudio?> ResolveAsync(string entryKey, AudioFormat requestedFormat)
+    {
+        if (requestedFormat == AudioFormat.Opus)
+        {
+            var opus = await _fileDatabase.LoadResourceAsync<AudioBinary>(
+                VaultConstants.TrackOpus, OpusTranscodeService.OpusAudioKey(entryKey));
+            if (opus is not null)
+                return new ResolvedAudio(opus, MimeTypeExtensions.GetMimeType(opus.Extension), AudioFormat.Opus);
+
+            // C2 fallback: no Opus artifact yet (legacy row, not backfilled, or transcode failed). Degrade
+            // to lossless rather than 404 — Opus is strictly additive; its absence never means "no audio".
+            _logger.LogInformation(
+                "Opus requested for {EntryKey} but no Opus artifact exists; falling back to lossless.", entryKey);
+        }
+
+        return await ResolveLosslessAsync(entryKey);
+    }
+
+    /// <summary>
+    /// Resolves the lossless source artifact and its real MIME — the existing read path, unchanged. Shared
+    /// by the explicit-lossless branch and the Opus fallback so both produce identical bytes + content-type.
+    /// </summary>
+    private async Task<ResolvedAudio?> ResolveLosslessAsync(string entryKey)
+    {
+        var source = await _trackContentService.GetAudioBinaryAsync(entryKey);
+        if (source is null)
+            return null;
+
+        return new ResolvedAudio(source, MimeTypeExtensions.GetMimeType(source.Extension), AudioFormat.Lossless);
+    }
+
+    /// <summary>
+    /// Returns the Opus setup-header + seek-index sidecar bytes for <paramref name="entryKey"/>, or null
+    /// when no sidecar is stored (no Opus artifact yet, or an older derive predating the sidecar). 18.3
+    /// serves these on their own path; 18.4 fetches them once on track load and parses them into the
+    /// client's <c>OpusSeekData</c>. The bytes are the raw <see cref="OpusSidecar"/> blob
+    /// (<c>[uint32 setupHeaderLength][setup-header][seek-index]</c>) exactly as 18.1 stored them.
+    /// </summary>
+    public async Task<byte[]?> GetOpusSidecarAsync(string entryKey)
+    {
+        var sidecar = await _fileDatabase.LoadResourceAsync<MediaBinary>(
+            VaultConstants.TrackOpus, OpusTranscodeService.OpusSidecarKey(entryKey));
+        return sidecar?.Buffer;
+    }
+}