Refactor and add scheduled task

src/Jellyfin.MediaEncoding.Hls/Cache/CacheDecorator.cs

@@ -0,0 +1,87 @@
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Globalization;
+using System.IO;
+using System.Text.Json;
+using Jellyfin.Extensions.Json;
+using Jellyfin.MediaEncoding.Hls.Extractors;
+using Jellyfin.MediaEncoding.Keyframes;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Common.Extensions;
+
+namespace Jellyfin.MediaEncoding.Hls.Cache;
+
+/// <inheritdoc />
+public class CacheDecorator : IKeyframeExtractor
+{
+    private readonly IKeyframeExtractor _keyframeExtractor;
+    private static readonly JsonSerializerOptions _jsonOptions = JsonDefaults.Options;
+    private readonly string _keyframeCachePath;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="CacheDecorator"/> class.
+    /// </summary>
+    /// <param name="applicationPaths">An instance of the <see cref="IApplicationPaths"/> interface.</param>
+    /// <param name="keyframeExtractor">An instance of the <see cref="IKeyframeExtractor"/> interface.</param>
+    public CacheDecorator(IApplicationPaths applicationPaths, IKeyframeExtractor keyframeExtractor)
+    {
+        _keyframeExtractor = keyframeExtractor;
+        ArgumentNullException.ThrowIfNull(applicationPaths);
+
+        // TODO make the dir configurable
+        _keyframeCachePath = Path.Combine(applicationPaths.DataPath, "keyframes");
+    }
+
+    /// <inheritdoc />
+    public bool IsMetadataBased => _keyframeExtractor.IsMetadataBased;
+
+    /// <inheritdoc />
+    public bool TryExtractKeyframes(string filePath, [NotNullWhen(true)] out KeyframeData? keyframeData)
+    {
+        keyframeData = null;
+        var cachePath = GetCachePath(_keyframeCachePath, filePath);
+        if (TryReadFromCache(cachePath, out var cachedResult))
+        {
+            keyframeData = cachedResult;
+            return true;
+        }
+
+        if (!_keyframeExtractor.TryExtractKeyframes(filePath, out var result))
+        {
+            return false;
+        }
+
+        keyframeData = result;
+        SaveToCache(cachePath, keyframeData);
+        return true;
+    }
+
+    private static void SaveToCache(string cachePath, KeyframeData keyframeData)
+    {
+        var json = JsonSerializer.Serialize(keyframeData, _jsonOptions);
+        Directory.CreateDirectory(Path.GetDirectoryName(cachePath) ?? throw new ArgumentException($"Provided path ({cachePath}) is not valid.", nameof(cachePath)));
+        File.WriteAllText(cachePath, json);
+    }
+
+    private static string GetCachePath(string keyframeCachePath, string filePath)
+    {
+        var lastWriteTimeUtc = File.GetLastWriteTimeUtc(filePath);
+        ReadOnlySpan<char> filename = (filePath + "_" + lastWriteTimeUtc.Ticks.ToString(CultureInfo.InvariantCulture)).GetMD5() + ".json";
+        var prefix = filename[..1];
+
+        return Path.Join(keyframeCachePath, prefix, filename);
+    }
+
+    private static bool TryReadFromCache(string cachePath, [NotNullWhen(true)] out KeyframeData? cachedResult)
+    {
+        if (File.Exists(cachePath))
+        {
+            var bytes = File.ReadAllBytes(cachePath);
+            cachedResult = JsonSerializer.Deserialize<KeyframeData>(bytes, _jsonOptions);
+            return cachedResult != null;
+        }
+
+        cachedResult = null;
+        return false;
+    }
+}