From fb12a0384e145eaaccf06149b633a25e0813a307 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Mon, 16 Sep 2019 19:18:19 -0700
Subject: [PATCH] modules/m_breadcrumb_rooms: Hook breadcrumb rooms to track
 focused room; prefetch viewport.

---
 modules/m_breadcrumb_rooms.cc | 128 ++++++++++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)

diff --git a/modules/m_breadcrumb_rooms.cc b/modules/m_breadcrumb_rooms.cc
index a37f18269..e9b2ddcde 100644
--- a/modules/m_breadcrumb_rooms.cc
+++ b/modules/m_breadcrumb_rooms.cc
@@ -8,12 +8,140 @@
 // copyright notice and this permission notice is present in all copies. The
 // full license for this software is available in the LICENSE file.
 
+namespace ircd::m
+{
+	static void handle_breadcrumb_rooms_focus_out(const event &, vm::eval &, const json::array &);
+	static void handle_breadcrumb_rooms_focus_in(const event &, vm::eval &, const json::array &);
+	static void handle_breadcrumb_rooms(const event &, vm::eval &);
+	extern hookfn<vm::eval &> hook_breadcrumb_rooms;
+}
+
 ircd::mapi::header
 IRCD_MODULE
 {
 	"Matrix Breadcrumb Rooms"
 };
 
+decltype(ircd::m::hook_breadcrumb_rooms)
+ircd::m::hook_breadcrumb_rooms
+{
+	handle_breadcrumb_rooms,
+	{
+		{ "_site",      "vm.effect"                        },
+		{ "type",       "ircd.account_data"                },
+		{ "state_key",  "im.vector.riot.breadcrumb_rooms"  },
+	},
+};
+
+void
+ircd::m::handle_breadcrumb_rooms(const event &event,
+                                 vm::eval &eval)
+try
+{
+	const m::user::id &sender
+	{
+		at<"sender"_>(event)
+	};
+
+	const m::user::room user_room
+	{
+		sender
+	};
+
+	// We only want to hook events in the user's user room.
+	if(at<"room_id"_>(event) != user_room.room_id)
+		return;
+
+	const auto &content
+	{
+		json::get<"content"_>(event)
+	};
+
+	const json::array &rooms
+	{
+		content.get("rooms")
+	};
+
+	handle_breadcrumb_rooms_focus_out(event, eval, rooms);
+	handle_breadcrumb_rooms_focus_in(event, eval, rooms);
+}
+catch(const ctx::interrupted &)
+{
+	throw;
+}
+catch(const std::exception &e)
+{
+	log::error
+	{
+		m::log, "breadcrumb_rooms hook :%s",
+		e.what(),
+	};
+}
+
+void
+ircd::m::handle_breadcrumb_rooms_focus_in(const event &event,
+                                          vm::eval &eval,
+                                          const json::array &rooms)
+{
+	const room::id &focus_in
+	{
+		valid(id::ROOM, json::string{rooms[0]})?
+			room::id{json::string{rooms[0]}}:
+			room::id{}
+	};
+
+	if(!focus_in)
+		return;
+
+	room::events it
+	{
+		focus_in
+	};
+
+	ssize_t prefetched(0), i(0);
+	const ssize_t prefetch_max
+	{
+		ssize_t(room::events::viewport_size) / 2
+	};
+
+	for(; it && i < prefetch_max / 2; ++i, --it)
+		prefetched += m::prefetch(it.event_idx());
+
+	log::debug
+	{
+		m::log, "Prefetched %zu/%zu viewport:%zu of %s for %s now in focus",
+		prefetched,
+		i,
+		prefetch_max,
+		string_view{focus_in},
+		at<"sender"_>(event),
+		rooms.size(),
+	};
+}
+
+void
+ircd::m::handle_breadcrumb_rooms_focus_out(const event &event,
+                                           vm::eval &eval,
+                                           const json::array &rooms)
+{
+	const room::id &focus_out
+	{
+		valid(id::ROOM, json::string{rooms[1]})?
+			room::id{json::string{rooms[1]}}:
+			room::id{}
+	};
+
+	if(!focus_out)
+		return;
+
+	log::debug
+	{
+		m::log, "%s for %s out of focus",
+		string_view{focus_out},
+		at<"sender"_>(event),
+	};
+}
+
 ircd::m::event::id::buf
 ircd::m::breadcrumb_rooms::set(const json::array &rooms)
 const