cdn download support on shards + clean up

LightlessSyncServer/LightlessSyncStaticFilesServer/Services/CDNDownloadsService.cs

@@ -0,0 +1,56 @@
+using System.IO;
+using System.Threading.Tasks;
+
+namespace LightlessSyncStaticFilesServer.Services;
+
+public class CDNDownloadsService
+{
+    public enum ResultStatus
+    {
+        Disabled,
+        Unauthorized,
+        NotFound,
+        Success
+    }
+
+    public readonly record struct Result(ResultStatus Status, FileInfo? File);
+
+    private readonly CDNDownloadUrlService _cdnDownloadUrlService;
+    private readonly CachedFileProvider _cachedFileProvider;
+
+    public CDNDownloadsService(CDNDownloadUrlService cdnDownloadUrlService, CachedFileProvider cachedFileProvider)
+    {
+        _cdnDownloadUrlService = cdnDownloadUrlService;
+        _cachedFileProvider = cachedFileProvider;
+    }
+
+    public bool DownloadsEnabled => _cdnDownloadUrlService.DirectDownloadsEnabled;
+
+    public async Task<Result> GetDownloadAsync(string hash, long expiresUnixSeconds, string signature)
+    {
+        if (!_cdnDownloadUrlService.DirectDownloadsEnabled)
+        {
+            return new Result(ResultStatus.Disabled, null);
+        }
+
+        if (string.IsNullOrEmpty(signature) || string.IsNullOrEmpty(hash))
+        {
+            return new Result(ResultStatus.Unauthorized, null);
+        }
+
+        hash = hash.ToUpperInvariant();
+
+        if (!_cdnDownloadUrlService.TryValidateSignature(hash, expiresUnixSeconds, signature))
+        {
+            return new Result(ResultStatus.Unauthorized, null);
+        }
+
+        var fileInfo = await _cachedFileProvider.DownloadAndGetLocalFileInfo(hash).ConfigureAwait(false);
+        if (fileInfo == null)
+        {
+            return new Result(ResultStatus.NotFound, null);
+        }
+
+        return new Result(ResultStatus.Success, fileInfo);
+    }
+}