From eb7f160b2398a556be6a51961430ab3da6fa805c Mon Sep 17 00:00:00 2001
From: Laura Hausmann <laura@hausmann.dev>
Date: Fri, 9 Feb 2024 11:37:38 +0100
Subject: [PATCH] [backend/federation] Handle note delete activities (ISH-12)

---
 .../ActivityPub/ActivityHandlerService.cs     | 11 +++++++--
 .../Core/Services/NoteService.cs              | 24 +++++++++++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/Iceshrimp.Backend/Core/Federation/ActivityPub/ActivityHandlerService.cs b/Iceshrimp.Backend/Core/Federation/ActivityPub/ActivityHandlerService.cs
index 5ac12cd1..59f1f8fb 100644
--- a/Iceshrimp.Backend/Core/Federation/ActivityPub/ActivityHandlerService.cs
+++ b/Iceshrimp.Backend/Core/Federation/ActivityPub/ActivityHandlerService.cs
@@ -33,12 +33,19 @@ public class ActivityHandlerService(
 
 		switch (activity) {
 			case ASCreate: {
-				//TODO: implement the rest
+				//TODO: should we handle other types of creates?
 				if (activity.Object is not ASNote note)
 					throw GracefulException.UnprocessableEntity("Create activity object is invalid");
 				await noteSvc.ProcessNoteAsync(note, activity.Actor);
 				return;
 			}
+			case ASDelete: {
+				//TODO: handle user deletes
+				if (activity.Object is not ASNote note)
+					throw GracefulException.UnprocessableEntity("Delete activity object is invalid");
+				await noteSvc.DeleteNoteAsync(note, activity.Actor);
+				return;
+			}
 			case ASFollow: {
 				if (activity.Object is not { } obj)
 					throw GracefulException.UnprocessableEntity("Follow activity object is invalid");
@@ -64,7 +71,7 @@ public class ActivityHandlerService(
 				return;
 			}
 			case ASUndo: {
-				//TODO: implement the rest
+				//TODO: what other types of undo objects are there?
 				if (activity.Object is not ASActivity { Type: ASActivity.Types.Follow, Object: not null } undoActivity)
 					throw new NotImplementedException("Unsupported undo operation");
 				await UnfollowAsync(undoActivity.Object, activity.Actor);
diff --git a/Iceshrimp.Backend/Core/Services/NoteService.cs b/Iceshrimp.Backend/Core/Services/NoteService.cs
index 88efa21e..136d2048 100644
--- a/Iceshrimp.Backend/Core/Services/NoteService.cs
+++ b/Iceshrimp.Backend/Core/Services/NoteService.cs
@@ -61,6 +61,30 @@ public class NoteService(
 		return note;
 	}
 
+	public async Task DeleteNoteAsync(ASNote note, ASActor actor) {
+		// ReSharper disable once EntityFramework.NPlusOne.IncompleteDataQuery (it doesn't know about IncludeCommonProperties())
+		var dbNote = await db.Notes.IncludeCommonProperties().FirstOrDefaultAsync(p => p.Uri == note.Id);
+		if (dbNote == null) {
+			logger.LogDebug("Note '{id}' isn't known, skipping", note.Id);
+			return;
+		}
+
+		var user = await userResolver.ResolveAsync(actor.Id);
+		
+		// ReSharper disable once EntityFramework.NPlusOne.IncompleteDataUsage (same reason as above)
+		if (dbNote.User != user) {
+			logger.LogDebug("Note '{id}' isn't owned by actor requesting its deletion, skipping", note.Id);
+			return;
+		}
+		
+		logger.LogDebug("Deleting note '{id}' owned by {userId}", note.Id, user.Id);
+
+		user.NotesCount--;
+		db.Remove(dbNote);
+
+		await db.SaveChangesAsync();
+	}
+
 	public async Task<Note> ProcessNoteAsync(ASNote note, ASActor actor) {
 		var dbHit = await db.Notes.IncludeCommonProperties().FirstOrDefaultAsync(p => p.Uri == note.Id);