From bcadecdc3b844e83253167c34e1689f6ad87919c Mon Sep 17 00:00:00 2001
From: timedout <git@nexy7574.co.uk>
Date: Wed, 17 Jun 2026 17:59:28 +0100
Subject: [PATCH] feat: Add `!admin debug rooms-by-extremity-count` command

---
 src/admin/debug/commands.rs    | 52 +++++++++++++++++++++++++++++++++-
 src/admin/debug/mod.rs         |  5 ++++
 src/service/rooms/state/mod.rs | 10 +++++++
 3 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/src/admin/debug/commands.rs b/src/admin/debug/commands.rs
index f9a678f19..87a81d893 100644
--- a/src/admin/debug/commands.rs
+++ b/src/admin/debug/commands.rs
@@ -31,7 +31,7 @@ use service::rooms::{
 };
 use tracing_subscriber::EnvFilter;
 
-use crate::admin_command;
+use crate::{PAGE_SIZE, admin_command};
 
 #[admin_command]
 pub(super) async fn echo(&self, message: Vec<String>) -> Result {
@@ -1138,3 +1138,53 @@ pub(super) async fn send_test_email(&self) -> Result {
 
 	Ok(())
 }
+
+#[admin_command]
+pub(super) async fn rooms_by_extremity_count(&self, page: Option<usize>) -> Result {
+	let page = page.unwrap_or(1);
+	// My Giant Chain:tm:
+	let mapped: HashMap<OwnedRoomId, u64> = self
+		.services
+		.rooms
+		.state
+		.all_forward_extremities()
+		.ready_fold(HashMap::new(), move |mut map, (room_id, _)| {
+			let count: u64 = map.get(&room_id).copied().unwrap_or(0);
+			map.insert(room_id, count.saturating_add(1));
+			map
+		})
+		.await
+		.into_iter()
+		.filter_map(|(room_id, count)| (count >= 2).then_some((room_id, count)))
+		.collect();
+	if mapped.is_empty() {
+		return Err!("No more rooms.");
+	}
+
+	let mut rooms = mapped.keys().collect::<Vec<_>>();
+	rooms.sort_by_key(|room_id| {
+		mapped
+			.get(*room_id)
+			.copied()
+			.expect("keys must have values")
+	});
+	rooms.reverse();
+
+	let body = rooms
+		.into_iter()
+		.stream()
+		.skip(page.saturating_sub(1).saturating_mul(PAGE_SIZE))
+		.take(PAGE_SIZE)
+		.map(|room_id| {
+			format!("{room_id}: {}", mapped.get(room_id).copied().expect("keys must have values"))
+		})
+		.collect::<Vec<_>>()
+		.await;
+
+	self.write_str(&format!(
+		"Rooms by extremity count ({}):\n```\n{}\n```",
+		body.len(),
+		body.join("\n")
+	))
+	.await
+}
diff --git a/src/admin/debug/mod.rs b/src/admin/debug/mod.rs
index a9478ce82..0a2e0ae7e 100644
--- a/src/admin/debug/mod.rs
+++ b/src/admin/debug/mod.rs
@@ -237,6 +237,11 @@ pub enum DebugCommand {
 	/// Send a test email to the invoking admin's email address
 	SendTestEmail,
 
+	/// Lists room IDs by forward extremity count in descending order
+	RoomsByExtremityCount {
+		page: Option<usize>,
+	},
+
 	/// Developer test stubs
 	#[command(subcommand)]
 	#[allow(non_snake_case)]
diff --git a/src/service/rooms/state/mod.rs b/src/service/rooms/state/mod.rs
index ccc4be87e..bb0061f08 100644
--- a/src/service/rooms/state/mod.rs
+++ b/src/service/rooms/state/mod.rs
@@ -371,6 +371,16 @@ impl Service {
 			.deserialized()
 	}
 
+	pub fn all_forward_extremities(
+		&self,
+	) -> impl Stream<Item = (OwnedRoomId, OwnedEventId)> + Send {
+		self.db
+			.roomid_pduleaves
+			.keys()
+			.map_ok(|(room_id, event_id): (OwnedRoomId, OwnedEventId)| (room_id, event_id))
+			.ignore_err()
+	}
+
 	pub fn get_forward_extremities<'a>(
 		&'a self,
 		room_id: &'a RoomId,