generate thumbnails

AobaCore/Services/ThumbnailService.cs

@@ -4,6 +4,9 @@ using MongoDB.Bson;
 using MongoDB.Driver;
 using MongoDB.Driver.GridFS;
 
+using SixLabors.ImageSharp;
+using SixLabors.ImageSharp.Processing;
+
 using System;
 using System.Collections.Generic;
 using System.Linq;
@@ -11,18 +14,42 @@ using System.Text;
 using System.Threading.Tasks;
 
 namespace AobaCore.Services;
-internal class ThumbnailService(IMongoDatabase db, AobaService aobaService)
+public class ThumbnailService(IMongoDatabase db, AobaService aobaService)
 {
 	private readonly GridFSBucket _gridfs = new GridFSBucket(db);
 	private readonly IMongoCollection<MeidaThumbnail> _thumbnails = db.GetCollection<MeidaThumbnail>("thumbs");
 
-	public async Task<MemoryStream> GetThumbnailAsync(ObjectId id)
+	public async Task<Stream?> GetThumbnailAsync(ObjectId id, CancellationToken cancellationToken = default)
 	{
-        throw new NotImplementedException();
+		var media = await aobaService.GetMediaAsync(id);
+		if (media == null)
+			return null;
+		if (media.MediaType != MediaType.Image)
+			return null;
+		using var file = await _gridfs.OpenDownloadStreamAsync(media.MediaId, new GridFSDownloadOptions { Seekable = true });
+		return await GenerateThumbnailAsync(file, cancellationToken);
+	}
+	public async Task<Stream?> GetThumbnailFromFileAsync(ObjectId id, CancellationToken cancellationToken = default)
+	{
+		var media = await aobaService.GetMediaFromFileAsync(id);
+		if (media == null)
+			return null;
+		if (media.MediaType != MediaType.Image)
+			return null;
+		using var file = await _gridfs.OpenDownloadStreamAsync(media.MediaId, new GridFSDownloadOptions { Seekable = true });
+		return await GenerateThumbnailAsync(file, cancellationToken);
 	}
 
-	public async Task GenerateThumbnailAsync(ObjectId id)
+	public async Task<Stream> GenerateThumbnailAsync(Stream stream, CancellationToken cancellationToken = default) 
 	{
-
+		var img = Image.Load(stream);
+		img.Mutate(o =>
+		{
+			o.Resize(200, 200);
+		});
+		var result = new MemoryStream();
+		await img.SaveAsWebpAsync(result, cancellationToken);
+		result.Position = 0;
+		return result;
 	}
 }